Fast Bitmap Blur For Android SDK

Question

Currently in an Android application that I'm developing I'm looping through the pixels of an image to blur it. This takes about 30 seconds on a 640x480 image.

While browsing apps in the Android Market I came across one that includes a blur feature and their blur is very fast (like 5 seconds) so they must be using a different method of blurring.

Anyone know a faster way other than looping through the pixels?

Reduplicative

Unfortunately the images will always be different so I won't be able create a blurred version ahead of time. Plus I won't know the blur intensity ahead of time either. – Reduplicative

Could you post your code, it maybe it is the algorithm/code that is inefficient, 30 secs to go through an 640x480 image is slow, I'd have thought 5 secs was slow to but then again depends on the processor. – Ewing

Answer 1

This is a shot in the dark, but you might try shrinking the image and then enlarging it again. This can be done with Bitmap.createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter). Make sure and set the filter parameter to true. It'll run in native code so it might be faster.

Sill

After some testing and the blurring that I'm doing this actual works well enough for me and it's fast. Thanks! – Reduplicative

If it works good. It's a shame we never got to the bottom of why it was inefficient. – Ewing

You might want to try createScaledBitmap and leaving the image the same size. It is blurring it for me :-( – Sculpsit

Here is a discussion on the meaning of the argument "filter": stackoverflow.com/questions/2895065 – Electrolyse

This is not exactly the way to got because of 2 reasons: 1) it needs the memory of the full image altough you are probably only using a downscaled one 2) you need to load the full image wich is slower - use loading with inSampleSize and BitmapFactory.decodeResource(), which is far superior solution to this. – Woolgrower

So what's the proper way to use it? First, do it with dstWidth/10 and then dstWidth*10? – Aconite

Answer 2

For future Googlers, here is an algorithm that I ported from Quasimondo. It's kind of a mix between a box blur and a gaussian blur, it's very pretty and quite fast too.

Update for people encountering the ArrayIndexOutOfBoundsException problem : @anthonycr in the comments provides this information :

I found that by replacing Math.abs with StrictMath.abs or some other abs implementation, the crash does not occur.

/**
 * Stack Blur v1.0 from
 * http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
 * Java Author: Mario Klingemann <mario at quasimondo.com>
 * http://incubator.quasimondo.com
 *
 * created Feburary 29, 2004
 * Android port : Yahel Bouaziz <yahel at kayenko.com>
 * http://www.kayenko.com
 * ported april 5th, 2012
 *
 * This is a compromise between Gaussian Blur and Box blur
 * It creates much better looking blurs than Box Blur, but is
 * 7x faster than my Gaussian Blur implementation.
 *
 * I called it Stack Blur because this describes best how this
 * filter works internally: it creates a kind of moving stack
 * of colors whilst scanning through the image. Thereby it
 * just has to add one new block of color to the right side
 * of the stack and remove the leftmost color. The remaining
 * colors on the topmost layer of the stack are either added on
 * or reduced by one, depending on if they are on the right or
 * on the left side of the stack.
 *  
 * If you are using this algorithm in your code please add
 * the following line:
 * Stack Blur Algorithm by Mario Klingemann <[email protected]>
 */

public Bitmap fastblur(Bitmap sentBitmap, float scale, int radius) {

    int width = Math.round(sentBitmap.getWidth() * scale);
    int height = Math.round(sentBitmap.getHeight() * scale);
    sentBitmap = Bitmap.createScaledBitmap(sentBitmap, width, height, false);

    Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);

    if (radius < 1) {
        return (null);
    }

    int w = bitmap.getWidth();
    int h = bitmap.getHeight();

    int[] pix = new int[w * h];
    Log.e("pix", w + " " + h + " " + pix.length);
    bitmap.getPixels(pix, 0, w, 0, 0, w, h);

    int wm = w - 1;
    int hm = h - 1;
    int wh = w * h;
    int div = radius + radius + 1;

    int r[] = new int[wh];
    int g[] = new int[wh];
    int b[] = new int[wh];
    int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
    int vmin[] = new int[Math.max(w, h)];

    int divsum = (div + 1) >> 1;
    divsum *= divsum;
    int dv[] = new int[256 * divsum];
    for (i = 0; i < 256 * divsum; i++) {
        dv[i] = (i / divsum);
    }

    yw = yi = 0;

    int[][] stack = new int[div][3];
    int stackpointer;
    int stackstart;
    int[] sir;
    int rbs;
    int r1 = radius + 1;
    int routsum, goutsum, boutsum;
    int rinsum, ginsum, binsum;

    for (y = 0; y < h; y++) {
        rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
        for (i = -radius; i <= radius; i++) {
            p = pix[yi + Math.min(wm, Math.max(i, 0))];
            sir = stack[i + radius];
            sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
            sir[2] = (p & 0x0000ff);
            rbs = r1 - Math.abs(i);
            rsum += sir[0] * rbs;
            gsum += sir[1] * rbs;
            bsum += sir[2] * rbs;
            if (i > 0) {
                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];
            } else {
                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];
            }
        }
        stackpointer = radius;

        for (x = 0; x < w; x++) {

            r[yi] = dv[rsum];
            g[yi] = dv[gsum];
            b[yi] = dv[bsum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;

            stackstart = stackpointer - radius + div;
            sir = stack[stackstart % div];

            routsum -= sir[0];
            goutsum -= sir[1];
            boutsum -= sir[2];

            if (y == 0) {
                vmin[x] = Math.min(x + radius + 1, wm);
            }
            p = pix[yw + vmin[x]];

            sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
            sir[2] = (p & 0x0000ff);

            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;

            stackpointer = (stackpointer + 1) % div;
            sir = stack[(stackpointer) % div];

            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];

            rinsum -= sir[0];
            ginsum -= sir[1];
            binsum -= sir[2];

            yi++;
        }
        yw += w;
    }
    for (x = 0; x < w; x++) {
        rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
        yp = -radius * w;
        for (i = -radius; i <= radius; i++) {
            yi = Math.max(0, yp) + x;

            sir = stack[i + radius];

            sir[0] = r[yi];
            sir[1] = g[yi];
            sir[2] = b[yi];

            rbs = r1 - Math.abs(i);

            rsum += r[yi] * rbs;
            gsum += g[yi] * rbs;
            bsum += b[yi] * rbs;

            if (i > 0) {
                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];
            } else {
                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];
            }

            if (i < hm) {
                yp += w;
            }
        }
        yi = x;
        stackpointer = radius;
        for (y = 0; y < h; y++) {
            // Preserve alpha channel: ( 0xff000000 & pix[yi] )
            pix[yi] = ( 0xff000000 & pix[yi] ) | ( dv[rsum] << 16 ) | ( dv[gsum] << 8 ) | dv[bsum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;

            stackstart = stackpointer - radius + div;
            sir = stack[stackstart % div];

            routsum -= sir[0];
            goutsum -= sir[1];
            boutsum -= sir[2];

            if (x == 0) {
                vmin[y] = Math.min(y + r1, hm) * w;
            }
            p = x + vmin[y];

            sir[0] = r[p];
            sir[1] = g[p];
            sir[2] = b[p];

            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;

            stackpointer = (stackpointer + 1) % div;
            sir = stack[stackpointer];

            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];

            rinsum -= sir[0];
            ginsum -= sir[1];
            binsum -= sir[2];

            yi += w;
        }
    }

    Log.e("pix", w + " " + h + " " + pix.length);
    bitmap.setPixels(pix, 0, w, 0, 0, w, h);

    return (bitmap);
}

Fullmouthed

This take half the time than blurring using ConvolutionMatrix. – Ministry

what should i pass as radius? – Popham

Long time since I posted this, but from what I recall, the bigger the radius, the blurrier the final image. The algorithm mixes the pixels in a circle "radius" wide. The final color of the pixel being modified is the average of all the pixel in the "radius" circle. – Fullmouthed

For radius larger than 1 sometimes you get ArrayIndexOutOfBoundsException. I will try to identify the problem. – Grilse

@MichaelLiberman I also encountered the same problem.Found out why yet? "g[yi] = dv[gsum];" -->error :java.lang.ArrayIndexOutOfBoundsException: length=112896; index=114021 – Classieclassification

@MichaelLiberman Did you ever identify the ArrayIndexOutOfBoundsException problem? We are having the same problem. – Ministry

@Mobistry Sorry, I do not remember how I fixed it. If I will find the old code I will post the solution here. – Grilse

@OlcayErtaş : That must be one big bitmap you are using :) – Fullmouthed

Note that this does not work if your app is not fullscreen, because the top toolbar is not taken into consideration. Once you set as a background you will see that the blue effects are off. – Cachexia

Optimize the function by scaling the bitmap first: int width = Math.round(sentBitmap.getWidth() * scale); int height = Math.round(sentBitmap.getHeight() * scale); sentBitmap = Bitmap.createScaledBitmap(sentBitmap, width, height, false); .Example of scale value: 0.2f. Radius needed is also smaller, so it is much much faster. – Toreutic

Thanks. I ported to Xamarin with no trouble. – Airdry

important to know: sentBitmap.getConfig() might return null, so you should have a fallback for it. For example, create the default config. Also, is it possible to have the exact same algorithm on Renderscript, to make it faster? – Morelli

What are recommended parameters for the scale and radius? – Infinity

@Infinity : It depends what effect you want to achieve. The higher the scale and the radius, the blurrier it gets. Also not that the higher the radius, the more cpu consuming the algorithm gets. – Fullmouthed

@Fullmouthed 21 I ended up using (0.2f, 10) – Infinity

@NigamPatro, Regretfully I didn't, as it was a side project that I am no longer working on. Is there a reason you don't want to use RenderScript now? – Grilse

@Grilse Renderscript is not working fine in all devices. Some devices its crashing. Till now I also not worked, but got to know from some other developers. – Warble

@OlcayErtaş and anyone else getting OOM error: add android:largeHeap="true" to your <application> in AndroidManifest.xml. I was experiencing this on various devices too. Now it's fixed! – Hind

Workaround is just checking the array length. if (rsum >= dv.length) { Log.e(TAG, "out of bound rsum: " + rsum); } else { r[yi] = dv[rsum]; } if (gsum >= dv.length) { Log.e(TAG, "out of bound gsum: " + gsum); } else { g[yi] = dv[gsum]; } if (bsum >= dv.length) { Log.e(TAG, "out of bound bsum: " + bsum); } else { b[yi] = dv[bsum]; } – Frida

Funny thing is when I launched the app in debug mode, blur worked fine. Looked into it and found that bitmap.getPixels() returned different int array (different size, different data order) than when launched in normal mode. After playing with it for a while, I just added a length check and moved on. It all works now. – Frida

Does anybody know why are int arrays used here? We can definetely use less memory if we instead use signed bytes or at least short for r, g and b arrays, maybe for others as well. – Geaghan

Ran into the known ArrayIndexOutOfBoundsException, and after some analysis, I believe it is caused by an incorrect optimization by the Dalvik VM. In the for loop immediately before the bad dereference, either the calculation of the rbs variable or the calculation of the gsum, rsum, or bsum variables are not being done right. I found that by replacing Math.abs with StrictMath.abs or some other abs implementation, the crash does not occur. Since StrictMath.abs itself delegates to Math.abs, it seems like it must be a bad optimization. – Greggs

Thanks! Optimized for less memory consumption and no copying: gist.github.com/Miha-x64/3fb489d13dbf69e1611a8fb688b57d3d – Armillas

It works for ImageView, but not for complex layouts with TextView (text won't be blurred). I will turn to RenderScript version. – Wastrel

Any ways to make it even faster? Maybe to make loops parallel somehow? – Aconite

Answer 3

Android Blur Guide 2016

with Showcase/Benchmark App and Source on GitHub. Also check out the Blur framework I'm currently working on: Dali.

After experimenting a lot I can now safely give you some solid recommendations that will make your life easier in Android when using the Android Framework.

Load and Use a down scaled Bitmap (for very blurry images)

Never use the full size of a Bitmap. The bigger the image the more needs to be blurred and also the higher the blur radius needs to be and usually, the higher the blur radius the longer the algorithm takes.

final BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 8;
Bitmap blurTemplate = BitmapFactory.decodeResource(getResources(), R.drawable.myImage, options);

This will load the bitmap with inSampleSize 8, so only 1/64 of the original image. Test what inSampleSize suits your needs, but keep it 2^n (2,4,8,...) to avoid degrading quality due to scaling. See Google doc for more

Another huge advantage is that bitmap loading will be really fast. In my early blur testing I figured that the longest time during the whole blur process was the image loading. So to load a 1920x1080 image from disk my Nexus 5 needed 500ms while the blurring only took another 250 ms or so.

Use Renderscript

Renderscript provides ScriptIntrinsicBlur which is a Gaussian blur filter. It has good visual quality and is just the fastest you realistically get on Android. Google claims to be "typically 2-3x faster than a multithreaded C implementation and often 10x+ faster than a Java implementation". Renderscript is really sophisticated (using the fastest processing device (GPU, ISP, etc.), etc.) and there is also the v8 support library for it making it compatible down to 2.2. Well at least in theory, through my own tests and reports from other devs it seems that it is not possible to use Renderscript blindly, since the hardware/driver fragmentation seems to cause problems with some devices, even with higher SDK level (e.g. I had troubles with the 4.1 Nexus S) so be careful and test on a lot of devices. Here's a simple example that will get you started:

//define this only once if blurring multiple times
RenderScript rs = RenderScript.create(context);

(...)
//this will blur the bitmapOriginal with a radius of 8 and save it in bitmapOriginal
final Allocation input = Allocation.createFromBitmap(rs, bitmapOriginal); //use this constructor for best performance, because it uses USAGE_SHARED mode which reuses memory
final Allocation output = Allocation.createTyped(rs, input.getType());
final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
script.setRadius(8f);
script.setInput(input);
script.forEach(output);
output.copyTo(bitmapOriginal);

When using the v8 support with Gradle, which is specifically recommended by Google "because they include the latest improvements", you only need to add 2 lines to your build script and use android.support.v8.renderscript with current build tools (updated syntax for android Gradle plugin v14+)

android {
    ...
    defaultConfig {
        ...
        renderscriptTargetApi 19
        renderscriptSupportModeEnabled true
    }
}

Simple benchmark on a Nexus 5 - comparing RenderScript with different other java and Renderscript implementations:

The average runtime per blur on different pic sizes

Megapixels per sec that can be blurred

Each value is the avg of 250 rounds. RS_GAUSS_FAST is ScriptIntrinsicBlur (and nearly always the fastest), others that start with RS_ are mostly convolve implementations with simple kernels. The details of the algorithms can be found here. This is not purely blurring, since a good portion is garbage collection that is measured. This can be seen in this here (ScriptIntrinsicBlur on a 100x100 image with about 500 rounds)

The spikes are gc.

You can check for yourself, the benchmark app is in the Playstore: BlurBenchmark

Reuses Bitmap wherever possible (if priority: performance > memory footprint)

If you need multiple blurs for a live blur or similar and your memory allows it, do not load the bitmap from drawables multiple times, but keep it "cached" in a member variable. In this case always try to use the same variables, to keep garbage collecting to a minimum.

Also check out the new inBitmap option when loading from a file or drawable which will reuse the bitmap memory and save garbage collection time.

For blending from sharp to blurry

The simple and naive method is just to use 2 ImageViews, one blurred, and alpha fade them. But if you want a more sophisticated look that smoothly fades from sharp to blurry, then check out Roman Nurik's post about how to do it like in his Muzei app.

Basically he explains that he pre-blurs some frames with different blur extents and uses them as key frames in an animation that looks really smooth.

Woolgrower

First of all, thanks for your hard work! But I got a question: "because it uses USAGE_SHARED mode which reuses memory". Where did you find the constant USAGE_SHARED? I couldn't find it anywhere. – Cwm

I found it, USAGE_SHARED is only available in support.v8.renderscript – Cwm

Man, this deserve to be SO UPVOTED that if i could, i would upvote a thousand times. :D – Doubleness

@SomeNoobStudent that's not true, USAGE_SHARED was added in API lvl 18, so your target is probably lower developer.android.com/reference/android/renderscript/… – Woolgrower

@for3st: I see, thank you again. Have you compared the memory/heap pressure between different methods? I hear scriptintrinsicblur can take up a lot of heap space... – Cwm

@SomeNoobStudent no, the tip is from json sams from the google renderscript team, I did not verify. Im not REALLY sure if renderscript memory allocations are on the heap, because it gets compiled to C afaik which would not be restricted/using heap memory. – Woolgrower

Renderscript fast Gaussian blur fails with C memory allocation errors on low end devices. Tested on ZTE Z992 (Android 4.1.1) and Kyocera Rise (Android 4.0.4) using the provided Play Store app. Also had a failure report on Samsung Galaxy S3 mini. Since errors occur in the C layer, they cannot be trapped as exceptions in Java, meaning an app crash is unavoidable. Looks like RenderScript may not ready for production use. – Gurl

Also, regular Gaussian fast blur fails on Nexus 5 (Android 4.4.4) with IllegalStateException when using the code or the Play Store test app. – Gurl

Best answer I've read on stackoverflow so far! Awesome job man :) – Stole

for newer gradle versions, use renderscriptSupportModeEnabled true or it will not build! I searched for ever! – Intermittent

thx @Intermittent ; the syntax change is for android gradle plugin v0.14+; Ive updated the answer – Woolgrower

When I tried this solution, rather than getting a blurred bitmap, I got a rainbow colored bitmap. Anyone else experience this problem? If so how did you fix it? – Sharie

Just started getting the same thing as @Sharie – Grandiose

This is faster than using on Java, but according to what I've noticed, it has relatively bad quality result, compared to the "fastBlur" solution of the other post (here: https://mcmap.net/q/127844/-fast-bitmap-blur-for-android-sdk ) . is it possible to convert their solution to RS? – Morelli

The idea of compressing the image to low quality and then blurring did the trick :) – Potter

Answer 4

EDIT (April 2014): This is a question/answer page that still gets a lot of hits it seems. I know I'm always getting upvotes for this post. But if you're reading this, you need to realize the answers posted here (both mine and the accepted answer) are out of date. If you want to implement efficient blur today, you should use RenderScript instead of the NDK or Java. RenderScript runs on Android 2.2+ (using the Android Support Library), so there's no reason not to use it.

The old answer follows, but beware as it's outdated.

---

For future² Googlers, here is an algorithm that I ported from Yahel's port of Quasimondo's algorithm, but using the NDK. It's based on Yahel's answer, of course. But this is running native C code, so it's faster. Much faster. Like, 40 times faster.

I find that using the NDK is how all image manipulation should be done on Android... it's somewhat annoying to implement at first (read a great tutorial on using JNI and the NDK here), but much better, and near real time for a lot of things.

For reference, using Yahel's Java function, it took 10 seconds to blur my 480x532 pixels image with a blur radius of 10. But it took 250ms using the native C version. And I'm pretty sure it can still be further optimized... I just did a dumb conversion of the java code, there's probably some manipulations that can be shortened, didn't want to spend too much time refactoring the whole thing.

#include <jni.h>
#include <string.h>
#include <math.h>
#include <stdio.h>
#include <android/log.h>
#include <android/bitmap.h>

#define LOG_TAG "libbitmaputils"
#define LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

typedef struct {
    uint8_t red;
    uint8_t green;
    uint8_t blue;
    uint8_t alpha;
} rgba;

JNIEXPORT void JNICALL Java_com_insert_your_package_ClassName_functionToBlur(JNIEnv* env, jobject obj, jobject bitmapIn, jobject bitmapOut, jint radius) {
    LOGI("Blurring bitmap...");

    // Properties
    AndroidBitmapInfo   infoIn;
    void*               pixelsIn;
    AndroidBitmapInfo   infoOut;
    void*               pixelsOut;

    int ret;

    // Get image info
    if ((ret = AndroidBitmap_getInfo(env, bitmapIn, &infoIn)) < 0 || (ret = AndroidBitmap_getInfo(env, bitmapOut, &infoOut)) < 0) {
        LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
        return;
    }

    // Check image
    if (infoIn.format != ANDROID_BITMAP_FORMAT_RGBA_8888 || infoOut.format != ANDROID_BITMAP_FORMAT_RGBA_8888) {
        LOGE("Bitmap format is not RGBA_8888!");
        LOGE("==> %d %d", infoIn.format, infoOut.format);
        return;
    }

    // Lock all images
    if ((ret = AndroidBitmap_lockPixels(env, bitmapIn, &pixelsIn)) < 0 || (ret = AndroidBitmap_lockPixels(env, bitmapOut, &pixelsOut)) < 0) {
        LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    }

    int h = infoIn.height;
    int w = infoIn.width;

    LOGI("Image size is: %i %i", w, h);

    rgba* input = (rgba*) pixelsIn;
    rgba* output = (rgba*) pixelsOut;

    int wm = w - 1;
    int hm = h - 1;
    int wh = w * h;
    int whMax = max(w, h);
    int div = radius + radius + 1;

    int r[wh];
    int g[wh];
    int b[wh];
    int rsum, gsum, bsum, x, y, i, yp, yi, yw;
    rgba p;
    int vmin[whMax];

    int divsum = (div + 1) >> 1;
    divsum *= divsum;
    int dv[256 * divsum];
    for (i = 0; i < 256 * divsum; i++) {
        dv[i] = (i / divsum);
    }

    yw = yi = 0;

    int stack[div][3];
    int stackpointer;
    int stackstart;
    int rbs;
    int ir;
    int ip;
    int r1 = radius + 1;
    int routsum, goutsum, boutsum;
    int rinsum, ginsum, binsum;

    for (y = 0; y < h; y++) {
        rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
        for (i = -radius; i <= radius; i++) {
            p = input[yi + min(wm, max(i, 0))];

            ir = i + radius; // same as sir

            stack[ir][0] = p.red;
            stack[ir][1] = p.green;
            stack[ir][2] = p.blue;
            rbs = r1 - abs(i);
            rsum += stack[ir][0] * rbs;
            gsum += stack[ir][1] * rbs;
            bsum += stack[ir][2] * rbs;
            if (i > 0) {
                rinsum += stack[ir][0];
                ginsum += stack[ir][1];
                binsum += stack[ir][2];
            } else {
                routsum += stack[ir][0];
                goutsum += stack[ir][1];
                boutsum += stack[ir][2];
            }
        }
        stackpointer = radius;

        for (x = 0; x < w; x++) {

            r[yi] = dv[rsum];
            g[yi] = dv[gsum];
            b[yi] = dv[bsum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;

            stackstart = stackpointer - radius + div;
            ir = stackstart % div; // same as sir

            routsum -= stack[ir][0];
            goutsum -= stack[ir][1];
            boutsum -= stack[ir][2];

            if (y == 0) {
                vmin[x] = min(x + radius + 1, wm);
            }
            p = input[yw + vmin[x]];

            stack[ir][0] = p.red;
            stack[ir][1] = p.green;
            stack[ir][2] = p.blue;

            rinsum += stack[ir][0];
            ginsum += stack[ir][1];
            binsum += stack[ir][2];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;

            stackpointer = (stackpointer + 1) % div;
            ir = (stackpointer) % div; // same as sir

            routsum += stack[ir][0];
            goutsum += stack[ir][1];
            boutsum += stack[ir][2];

            rinsum -= stack[ir][0];
            ginsum -= stack[ir][1];
            binsum -= stack[ir][2];

            yi++;
        }
        yw += w;
    }
    for (x = 0; x < w; x++) {
        rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
        yp = -radius * w;
        for (i = -radius; i <= radius; i++) {
            yi = max(0, yp) + x;

            ir = i + radius; // same as sir

            stack[ir][0] = r[yi];
            stack[ir][1] = g[yi];
            stack[ir][2] = b[yi];

            rbs = r1 - abs(i);

            rsum += r[yi] * rbs;
            gsum += g[yi] * rbs;
            bsum += b[yi] * rbs;

            if (i > 0) {
                rinsum += stack[ir][0];
                ginsum += stack[ir][1];
                binsum += stack[ir][2];
            } else {
                routsum += stack[ir][0];
                goutsum += stack[ir][1];
                boutsum += stack[ir][2];
            }

            if (i < hm) {
                yp += w;
            }
        }
        yi = x;
        stackpointer = radius;
        for (y = 0; y < h; y++) {
            output[yi].red = dv[rsum];
            output[yi].green = dv[gsum];
            output[yi].blue = dv[bsum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;

            stackstart = stackpointer - radius + div;
            ir = stackstart % div; // same as sir

            routsum -= stack[ir][0];
            goutsum -= stack[ir][1];
            boutsum -= stack[ir][2];

            if (x == 0) vmin[y] = min(y + r1, hm) * w;
            ip = x + vmin[y];

            stack[ir][0] = r[ip];
            stack[ir][1] = g[ip];
            stack[ir][2] = b[ip];

            rinsum += stack[ir][0];
            ginsum += stack[ir][1];
            binsum += stack[ir][2];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;

            stackpointer = (stackpointer + 1) % div;
            ir = stackpointer; // same as sir

            routsum += stack[ir][0];
            goutsum += stack[ir][1];
            boutsum += stack[ir][2];

            rinsum -= stack[ir][0];
            ginsum -= stack[ir][1];
            binsum -= stack[ir][2];

            yi += w;
        }
    }

    // Unlocks everything
    AndroidBitmap_unlockPixels(env, bitmapIn);
    AndroidBitmap_unlockPixels(env, bitmapOut);

    LOGI ("Bitmap blurred.");
}

int min(int a, int b) {
    return a > b ? b : a;
}

int max(int a, int b) {
    return a > b ? a : b;
}

Then use it like this (considering a class called com.insert.your.package.ClassName and a native function called functionToBlur, as the code above states):

// Create a copy
Bitmap bitmapOut = bitmapIn.copy(Bitmap.Config.ARGB_8888, true);
// Blur the copy
functionToBlur(bitmapIn, bitmapOut, __radius);

It expects a RGB_8888 bitmap!

To use a RGB_565 bitmap, either create a converted copy before passing the parameter (yuck), or change the function to use a new rgb565 type instead of rgba:

typedef struct {
    uint16_t byte0;
} rgb565;

The problem is that if you do that you can't read .red, .green and .blue of the pixel anymore, you need to read the byte properly, duh. When I needed that before, I did this:

r = (pixels[x].byte0 & 0xF800) >> 8;
g = (pixels[x].byte0 & 0x07E0) >> 3;
b = (pixels[x].byte0 & 0x001F) << 3;

But there's probably some less dumb way of doing it. I'm not much of a low-level C coder, I'm afraid.

Biotechnology

BUT it requires a lot of memory. To reduce memory consumption change type of r[wh], g[wh] and b[wh] to uint8_t. – Herein

can you show me what your Android.mk file looks like, on pastebin.com – Baggott

@CQM: Sure: pastebin.com/8VMTZy85 Consider, though, that using RenderScript is probably an easier, more modern, and potentially faster solution to this problem (only available on Android 4+, though). – Biotechnology

@zeh, I implemented this last evening. It is fast enough, but what values should I pass in for Radius, I put in "5" arbitrarily, but I don't understand the consequences (time, vs aesthetic of blur), should this be a dynamic variable based on resolution ? – Baggott

@CQM: It should be whatever you want to blur it with. The higher the number, the more blurred it is. I'm also using an arbitrary value of 14, but that's because I have static source images that always have the same size. Depending on what you need and how you present it, you may need to take the device resolution or image size into account. I haven't measured the time impact of different values for radius. Because this is a box blur, I'm assuming there's some degradation of the effect if the radius is too high, but I haven't analyzed the algorithm enough to be sure. – Biotechnology

@zeh, can you tell please how to replace output[yi].red = dv[rsum]; output[yi].green = dv[gsum]; output[yi].blue = dv[bsum]; for RGB_565 images? – Stetson

@Biotechnology do you have a renderscript example? – Wellpreserved

@Chris.Jenkins: I don't, I just know it's supposed to do that based on the documentation. – Biotechnology

For a working RenderScript example of a Gaussian Blur on Android SDK 17+ look here: https://mcmap.net/q/129978/-android-fast-bitmap-blur – Grube

RenderScript is also available as part of the support lib for Android 2.2+, so there's no reason not to use it everywhere anymore: android-developers.blogspot.com/2013/09/… – Biotechnology

this is fast but for some reason, i couldn't get it to run on a AsyncTask's doInBackground. When I run it on doInBackground, it would always fail – Something

Is there some example project, which utilizes RenderScript with the support lib? – Intermittent

Answer 5

This code is work perfect for me

Bitmap tempbg = BitmapFactory.decodeResource(getResources(),R.drawable.b1); //Load a background.
Bitmap final_Bitmap = BlurImage(tempbg);


@SuppressLint("NewApi")
Bitmap BlurImage (Bitmap input)
{
    try
    {
    RenderScript  rsScript = RenderScript.create(getApplicationContext());
    Allocation alloc = Allocation.createFromBitmap(rsScript, input);

    ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rsScript,   Element.U8_4(rsScript));
    blur.setRadius(21);
    blur.setInput(alloc);

    Bitmap result = Bitmap.createBitmap(input.getWidth(), input.getHeight(), Bitmap.Config.ARGB_8888);
    Allocation outAlloc = Allocation.createFromBitmap(rsScript, result);

    blur.forEach(outAlloc);
    outAlloc.copyTo(result);

    rsScript.destroy();
    return result;
    }
    catch (Exception e) {
        // TODO: handle exception
        return input;
    }

}

Corfu

Simplest way to blurring image (y) – Paraboloid

Thanks! Don't forget to add RenderScript in build.gradle. This method requires Bitmap, so first copy bitmap from a view, then call BlurImage(bitmap). – Wastrel

Renderscript is deprecated. Any other ways to achieve this? – Aconite

Answer 6

You can now use ScriptIntrinsicBlur from the RenderScript library to blur quickly. Here is how to access the RenderScript API. The following is a class I made to blur Views and Bitmaps:

public class BlurBuilder {
    private static final float BITMAP_SCALE = 0.4f;
    private static final float BLUR_RADIUS = 7.5f;

    public static Bitmap blur(View v) {
        return blur(v.getContext(), getScreenshot(v));
    }

    public static Bitmap blur(Context ctx, Bitmap image) {
        int width = Math.round(image.getWidth() * BITMAP_SCALE);
        int height = Math.round(image.getHeight() * BITMAP_SCALE);

        Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
        Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

        RenderScript rs = RenderScript.create(ctx);
        ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
        Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
        Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
        theIntrinsic.setRadius(BLUR_RADIUS);
        theIntrinsic.setInput(tmpIn);
        theIntrinsic.forEach(tmpOut);
        tmpOut.copyTo(outputBitmap);

        return outputBitmap;
    }

    private static Bitmap getScreenshot(View v) {
        Bitmap b = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(b);
        v.draw(c);
        return b;
    }
}

Cagliostro

The Renderscript context should not be created in the blur method, but managed statically or given to the method. (if you mind performance) – Woolgrower

Can you give an example of this is use? When I try to use it I get the following error: java.lang.IllegalArgumentException: width and height must be > 0 – Fullblown

@DonalRafferty, this is because in onCreate views have not been measured yet. We should do this after a short delay. – Wastrel

Answer 7

This worked fine for me: How to Blur Images Efficiently with Android's RenderScript

public class BlurBuilder {
    private static final float BITMAP_SCALE = 0.4f;
    private static final float BLUR_RADIUS = 7.5f;

    @SuppressLint("NewApi")
    public static Bitmap blur(Context context, Bitmap image) {
        int width = Math.round(image.getWidth() * BITMAP_SCALE);
        int height = Math.round(image.getHeight() * BITMAP_SCALE);

        Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height,
            false);
        Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

        RenderScript rs = RenderScript.create(context);
        ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs,
            Element.U8_4(rs));
        Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
        Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
        theIntrinsic.setRadius(BLUR_RADIUS);
        theIntrinsic.setInput(tmpIn);
        theIntrinsic.forEach(tmpOut);
        tmpOut.copyTo(outputBitmap);

        return outputBitmap;
    }
}

Rehearsal

This would be even better/faster if you cached the RenderScript object that you created. Instantiating a new one every time you want to blur an image just adds unnecessary overhead (Java object creation/destruction). – Chilcote

It is c copy of b_yng solution. – Wastrel

Answer 8

I used this before..

public static Bitmap myblur(Bitmap image, Context context) {
            final float BITMAP_SCALE = 0.4f;
            final float BLUR_RADIUS = 7.5f;
            int width = Math.round(image.getWidth() * BITMAP_SCALE);
            int height = Math.round(image.getHeight() * BITMAP_SCALE);
            Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
            Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);
            RenderScript rs = RenderScript.create(context);
            ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
            Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
            Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
            theIntrinsic.setRadius(BLUR_RADIUS);
            theIntrinsic.setInput(tmpIn);
            theIntrinsic.forEach(tmpOut);
            tmpOut.copyTo(outputBitmap);
            return outputBitmap;
        }

Usance

Answer 9

Thanks @Yahel for the code. Posting the same method with alpha channel blurring support as it took me some time to make it work correctly so it may save someone's time:

/**
 * Stack Blur v1.0 from
 * http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
 * Java Author: Mario Klingemann <mario at quasimondo.com>
 * http://incubator.quasimondo.com
 * <p/>
 * created Feburary 29, 2004
 * Android port : Yahel Bouaziz <yahel at kayenko.com>
 * http://www.kayenko.com
 * ported april 5th, 2012
 * <p/>
 * This is a compromise between Gaussian Blur and Box blur
 * It creates much better looking blurs than Box Blur, but is
 * 7x faster than my Gaussian Blur implementation.
 * <p/>
 * I called it Stack Blur because this describes best how this
 * filter works internally: it creates a kind of moving stack
 * of colors whilst scanning through the image. Thereby it
 * just has to add one new block of color to the right side
 * of the stack and remove the leftmost color. The remaining
 * colors on the topmost layer of the stack are either added on
 * or reduced by one, depending on if they are on the right or
 * on the left side of the stack.
 * <p/>
 * If you are using this algorithm in your code please add
 * the following line:
 * Stack Blur Algorithm by Mario Klingemann <[email protected]>
 */

public static Bitmap fastblur(Bitmap sentBitmap, float scale, int radius) {

    int width = Math.round(sentBitmap.getWidth() * scale);
    int height = Math.round(sentBitmap.getHeight() * scale);
    sentBitmap = Bitmap.createScaledBitmap(sentBitmap, width, height, false);

    Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);

    if (radius < 1) {
        return (null);
    }

    int w = bitmap.getWidth();
    int h = bitmap.getHeight();

    int[] pix = new int[w * h];
    Log.e("pix", w + " " + h + " " + pix.length);
    bitmap.getPixels(pix, 0, w, 0, 0, w, h);

    int wm = w - 1;
    int hm = h - 1;
    int wh = w * h;
    int div = radius + radius + 1;

    int r[] = new int[wh];
    int g[] = new int[wh];
    int b[] = new int[wh];
    int a[] = new int[wh];
    int rsum, gsum, bsum, asum, x, y, i, p, yp, yi, yw;
    int vmin[] = new int[Math.max(w, h)];

    int divsum = (div + 1) >> 1;
    divsum *= divsum;
    int dv[] = new int[256 * divsum];
    for (i = 0; i < 256 * divsum; i++) {
        dv[i] = (i / divsum);
    }

    yw = yi = 0;

    int[][] stack = new int[div][4];
    int stackpointer;
    int stackstart;
    int[] sir;
    int rbs;
    int r1 = radius + 1;
    int routsum, goutsum, boutsum, aoutsum;
    int rinsum, ginsum, binsum, ainsum;

    for (y = 0; y < h; y++) {
        rinsum = ginsum = binsum = ainsum = routsum = goutsum = boutsum = aoutsum = rsum = gsum = bsum = asum = 0;
        for (i = -radius; i <= radius; i++) {
            p = pix[yi + Math.min(wm, Math.max(i, 0))];
            sir = stack[i + radius];
            sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
            sir[2] = (p & 0x0000ff);
            sir[3] = 0xff & (p >> 24);

            rbs = r1 - Math.abs(i);
            rsum += sir[0] * rbs;
            gsum += sir[1] * rbs;
            bsum += sir[2] * rbs;
            asum += sir[3] * rbs;
            if (i > 0) {
                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];
                ainsum += sir[3];
            } else {
                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];
                aoutsum += sir[3];
            }
        }
        stackpointer = radius;

        for (x = 0; x < w; x++) {

            r[yi] = dv[rsum];
            g[yi] = dv[gsum];
            b[yi] = dv[bsum];
            a[yi] = dv[asum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;
            asum -= aoutsum;

            stackstart = stackpointer - radius + div;
            sir = stack[stackstart % div];

            routsum -= sir[0];
            goutsum -= sir[1];
            boutsum -= sir[2];
            aoutsum -= sir[3];

            if (y == 0) {
                vmin[x] = Math.min(x + radius + 1, wm);
            }
            p = pix[yw + vmin[x]];

            sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
            sir[2] = (p & 0x0000ff);
            sir[3] = 0xff & (p >> 24);

            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];
            ainsum += sir[3];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;
            asum += ainsum;

            stackpointer = (stackpointer + 1) % div;
            sir = stack[(stackpointer) % div];

            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];
            aoutsum += sir[3];

            rinsum -= sir[0];
            ginsum -= sir[1];
            binsum -= sir[2];
            ainsum -= sir[3];

            yi++;
        }
        yw += w;
    }
    for (x = 0; x < w; x++) {
        rinsum = ginsum = binsum = ainsum = routsum = goutsum = boutsum = aoutsum = rsum = gsum = bsum = asum = 0;
        yp = -radius * w;
        for (i = -radius; i <= radius; i++) {
            yi = Math.max(0, yp) + x;

            sir = stack[i + radius];

            sir[0] = r[yi];
            sir[1] = g[yi];
            sir[2] = b[yi];
            sir[3] = a[yi];

            rbs = r1 - Math.abs(i);

            rsum += r[yi] * rbs;
            gsum += g[yi] * rbs;
            bsum += b[yi] * rbs;
            asum += a[yi] * rbs;

            if (i > 0) {
                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];
                ainsum += sir[3];
            } else {
                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];
                aoutsum += sir[3];
            }

            if (i < hm) {
                yp += w;
            }
        }
        yi = x;
        stackpointer = radius;
        for (y = 0; y < h; y++) {
            pix[yi] = (dv[asum] << 24) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];

            rsum -= routsum;
            gsum -= goutsum;
            bsum -= boutsum;
            asum -= aoutsum;

            stackstart = stackpointer - radius + div;
            sir = stack[stackstart % div];

            routsum -= sir[0];
            goutsum -= sir[1];
            boutsum -= sir[2];
            aoutsum -= sir[3];

            if (x == 0) {
                vmin[y] = Math.min(y + r1, hm) * w;
            }
            p = x + vmin[y];


            sir[0] = r[p];
            sir[1] = g[p];
            sir[2] = b[p];
            sir[3] = a[p];

            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];
            ainsum += sir[3];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;
            asum += ainsum;

            stackpointer = (stackpointer + 1) % div;
            sir = stack[stackpointer];

            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];
            aoutsum += sir[3];

            rinsum -= sir[0];
            ginsum -= sir[1];
            binsum -= sir[2];
            ainsum -= sir[3];

            yi += w;
        }
    }

    Log.e("pix", w + " " + h + " " + pix.length);
    bitmap.setPixels(pix, 0, w, 0, 0, w, h);

    return (bitmap);
}

Scale

still with 'index out of range' in devices >hdpi as the original source – Enate

The algorithm is fine for premultiplied color values but getPixels() gives us unpremultiplied ones. If the config is ARGB_8888, you can use copyPixelsFrom/ToBuffer instead of get/setPixels: pixel color values will be premultiplied AABBGGRR (this also saves some (negligible) cycles on color conversion). – Armillas

Answer 10

Use Render Script as mentioned here http://blog.neteril.org/blog/2013/08/12/blurring-images-on-android/

Plymouth

Answer 11

This is for all people who need to increase the radius of ScriptIntrinsicBlur to obtain a harder gaussian blur.

Instead of to put the radius more than 25, you can scale down the image and get the same result. I wrote a class called GaussianBlur. Below you can see how to use, and the whole class implementation.

Usage:

GaussianBlur gaussian = new GaussianBlur(context);
gaussian.setMaxImageSize(60);
gaussian.setRadius(25); //max

Bitmap output = gaussian.render(<your bitmap>,true);
Drawable d = new BitmapDrawable(getResources(),output);

Class:

 public class GaussianBlur {
    private final int DEFAULT_RADIUS = 25;
    private final float DEFAULT_MAX_IMAGE_SIZE = 400;

    private Context context;
    private int radius;
    private float maxImageSize;

    public GaussianBlur(Context context) {
    this.context = context;
    setRadius(DEFAULT_RADIUS);
    setMaxImageSize(DEFAULT_MAX_IMAGE_SIZE);
    } 

    public Bitmap render(Bitmap bitmap, boolean scaleDown) {
    RenderScript rs = RenderScript.create(context);

    if (scaleDown) {
        bitmap = scaleDown(bitmap);
    }

    Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Config.ARGB_8888);

    Allocation inAlloc = Allocation.createFromBitmap(rs, bitmap, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_GRAPHICS_TEXTURE);
    Allocation outAlloc = Allocation.createFromBitmap(rs, output);

    ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, inAlloc.getElement()); // Element.U8_4(rs));
    script.setRadius(getRadius());
    script.setInput(inAlloc);
    script.forEach(outAlloc);
    outAlloc.copyTo(output);

    rs.destroy();

    return output;
}

public Bitmap scaleDown(Bitmap input) {
    float ratio = Math.min((float) getMaxImageSize() / input.getWidth(), (float) getMaxImageSize() / input.getHeight());
    int width = Math.round((float) ratio * input.getWidth());
    int height = Math.round((float) ratio * input.getHeight());

    return Bitmap.createScaledBitmap(input, width, height, true);
}

public int getRadius() {
    return radius;
}

public void setRadius(int radius) {
    this.radius = radius;
}

public float getMaxImageSize() {
    return maxImageSize;
}

public void setMaxImageSize(float maxImageSize) {
    this.maxImageSize = maxImageSize;
}
    }

Winifredwinikka

no if you scale down the image to scale up later you will retrieve a blocky image instead of a blured image :( – Diplo

Answer 12

For future Googlers who choose NDK approach - i find reliable mentioned stackblur algorithm. I found C++ implementation which does not rely on SSE here - http://www.antigrain.com/__code/include/agg_blur.h.html#stack_blur_rgba32 which contains some optimizations using static tables like:

static unsigned short const stackblur_mul[255] =
{
    512,512,456,512,328,456,335,512,405,328,271,456,388,335,292,512,
    454,405,364,328,298,271,496,456,420,388,360,335,312,292,273,512,
    482,454,428,405,383,364,345,328,312,298,284,271,259,496,475,456,
    437,420,404,388,374,360,347,335,323,312,302,292,282,273,265,512,
    497,482,468,454,441,428,417,405,394,383,373,364,354,345,337,328,
    320,312,305,298,291,284,278,271,265,259,507,496,485,475,465,456,
    446,437,428,420,412,404,396,388,381,374,367,360,354,347,341,335,
    329,323,318,312,307,302,297,292,287,282,278,273,269,265,261,512,
    505,497,489,482,475,468,461,454,447,441,435,428,422,417,411,405,
    399,394,389,383,378,373,368,364,359,354,350,345,341,337,332,328,
    324,320,316,312,309,305,301,298,294,291,287,284,281,278,274,271,
    268,265,262,259,257,507,501,496,491,485,480,475,470,465,460,456,
    451,446,442,437,433,428,424,420,416,412,408,404,400,396,392,388,
    385,381,377,374,370,367,363,360,357,354,350,347,344,341,338,335,
    332,329,326,323,320,318,315,312,310,307,304,302,299,297,294,292,
    289,287,285,282,280,278,275,273,271,269,267,265,263,261,259
};

static unsigned char const stackblur_shr[255] =
{
    9, 11, 12, 13, 13, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17,
    17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19,
    19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 20, 20, 20,
    20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 21,
    21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
    21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22,
    22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
    22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 23,
    23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
    23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
    23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
    23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24
}; 

I made modification of stackblur algorithm for multi-core systems - it can be found here http://vitiy.info/stackblur-algorithm-multi-threaded-blur-for-cpp/ As more and more devices have 4 cores - optimizations give 4x speed benefit.

Sealskin

Answer 13

Nicolas POMEPUY advice. I think this link will be helpful: Blur effect for Android design

Sample project at github

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
private static Bitmap fastblur16(Bitmap source, int radius, Context ctx) {    
    Bitmap bitmap = source.copy(source.getConfig(), true);    
    RenderScript rs = RenderScript.create(ctx);
    Allocation input = Allocation.createFromBitmap(rs, source, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT);
    Allocation output = Allocation.createTyped(rs, input.getType());
    ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
    script.setRadius(radius);
    script.setInput(input);
    script.forEach(output);
    output.copyTo(bitmap);
    return bitmap;
}

Diahann

While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. – Sestina

Amal Murali, you are right. Now change my post. Good, that you not only downvote, but also comment. – Diahann

Answer 14

We tried to implement RenderScript blur like mentioned above in different answers. We were limited to use the v8 RenderScript version and that caused us a lot of trouble.

• Samsung S3 crashed randomly whenever we tried to use the renderscript
• Other devices (across different APIs) randomly showed different color issues

I want to share our dirty Java-only version which is slow and should be done on a separate thread and, if possible, before usage and therefore persisted.

private final Paint mPaint = new Paint();

public Bitmap blur(final String pathToBitmap) {
    final BitmapFactory.Options options = new BitmapFactory.Options();
    final Bitmap normalOne = BitmapFactory.decodeFile(pathToBitmap, options);
    final Bitmap resultBitmap = Bitmap.createBitmap(options.outWidth, options.outHeight, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(resultBitmap);
    mPaint.setAlpha(180);
    canvas.drawBitmap(normalOne, 0, 0, mPaint);
    int blurRadius = 12;
    for (int row = -blurRadius; row < blurRadius; row += 2) {
        for (int col = -blurRadius; col < blurRadius; col += 2) {
            if (col * col + row * row <= blurRadius * blurRadius) {
                mPaint.setAlpha((blurRadius * blurRadius) / ((col * col + row * row) + 1) * 2);
                canvas.drawBitmap(normalOne, row, col, mPaint);
            }
        }
    }
    normalOne.recycle();
    return resultBitmap;
}

This solution is far from perfect but creates a reasonable blur effect based on the fact, that it draws highly transparent version of the same image on top of a barely transparent "sharp" version. The alpha depends on the distance to the origin.

You can adjust some "magic numbers" to your needs. I just wanted to share that "solution" for everybody who has issues with the v8 support version of RenderScript.

Denaturalize

Im also having an issue with RenderScript on some old armeabi devices, but your solution is too memory consuming. – Takeo

Answer 15

On the i/o 2019 the following solution was presented:

/**
 * Blurs the given Bitmap image
 * @param bitmap Image to blur
 * @param applicationContext Application context
 * @return Blurred bitmap image
 */
@WorkerThread
fun blurBitmap(bitmap: Bitmap, applicationContext: Context): Bitmap {
    lateinit var rsContext: RenderScript
    try {

        // Create the output bitmap
        val output = Bitmap.createBitmap(
                bitmap.width, bitmap.height, bitmap.config)

        // Blur the image
        rsContext = RenderScript.create(applicationContext, RenderScript.ContextType.DEBUG)
        val inAlloc = Allocation.createFromBitmap(rsContext, bitmap)
        val outAlloc = Allocation.createTyped(rsContext, inAlloc.type)
        val theIntrinsic = ScriptIntrinsicBlur.create(rsContext, Element.U8_4(rsContext))
        theIntrinsic.apply {
            setRadius(10f)
            theIntrinsic.setInput(inAlloc)
            theIntrinsic.forEach(outAlloc)
        }
        outAlloc.copyTo(output)

        return output
    } finally {
        rsContext.finish()
    }
}

Incredible

Answer 16

As of 2024, RenderScript is no longer the best approach to achieve blurring in Android.

Device and component manufacturers have already stopped providing hardware acceleration support, and RenderScript support is expected to be removed entirely in a future release. Source

The Toolkit is around to replace the RenderScript. I was able to achieve blur on a bitmap of 640x360 in ~9-12 milliseconds.

Here are the steps to follow to achieve the blur on a bitmap using the Toolkit.

1- Add the dependency:

implementation "com.github.android:renderscript-intrinsics-replacement-toolkit:b6363490c3"

2- And then call the blur function in the Toolkit. Note there are many other operations like blend and convolve which you can perform.

Toolkit.blur(sourceBitmap, 25)

Here sourceBitmap is the bitmap to blur and 25 is the radius. You can try out a radius from 1 to 25 to get the required results.

Anethole

Answer 17

For those still having issues with Renderscript support library on x86 chipsets, please have a look at this post by the creator of the library. It looks like the fix he prepared didn't make it somehow to the Build Tools v20.0.0, so he provides the files to fix it manually and a brief explanation of how to do it.

https://code.google.com/p/android/issues/detail?can=2&start=0&num=100&q=&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars&groupby=&sort=&id=71347

Serapis

Answer 18

from Mario Viviani blog one can use this solution from 17 Android Version:

https://plus.google.com/+MarioViviani/posts/fhuzYkji9zz

or

https://gist.github.com/Mariuxtheone/903c35b4927c0df18cf8

Sf

Answer 19

Here is a realtime blurring overlay using RenderScript, which seems to be fast enough.

https://github.com/mmin18/RealtimeBlurView

Piles

Answer 20

I found that decreasing contrast, brightness and saturation a little makes blurred images more pretty so I combined various methods from stack overflow and made this Blur Class which deals with blurring images, changing brightness, saturation, contrast and size of the blurred images. It can also convert images from drawable to bitmap and vice-versa.

Salsbury