Converting RGB data into a bitmap in Objective-C++ Cocoa

Question

I have a buffer of RGB unsigned char that I would like converted into a bitmap file, does anyone know how?

My RGB float is of the following format

R [(0,0)], G[(0,0)], B[(0,0)],R [(0,1)], G[(0,1)], B[(0,1)], R [(0,2)], G[(0,2)], B[(0,2)] .....

The values for each data unit ranges from 0 to 255. anyone has any ideas how I can go about making this conversion?

Tombstone

can you help me here please – Fabiola

Answer 1

You can use CGBitmapContextCreate to make a bitmap context from your raw data. Then you can create a CGImageRef from the bitmap context and save it. Unfortunately CGBitmapContextCreate is a little picky about the format of the data. It does not support 24-bit RGB data. The loop at the beginning swizzles the rgb data to rgba with an alpha value of zero at the end. You have to include and link with ApplicationServices framework.

char* rgba = (char*)malloc(width*height*4);
for(int i=0; i < width*height; ++i) {
    rgba[4*i] = myBuffer[3*i];
    rgba[4*i+1] = myBuffer[3*i+1];
    rgba[4*i+2] = myBuffer[3*i+2];
    rgba[4*i+3] = 0;
}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef bitmapContext = CGBitmapContextCreate(
    rgba,
    width,
    height,
    8, // bitsPerComponent
    4*width, // bytesPerRow
    colorSpace,
    kCGImageAlphaNoneSkipLast);

CFRelease(colorSpace);

CGImageRef cgImage = CGBitmapContextCreateImage(bitmapContext);
CFURLRef url = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, CFSTR("image.png"), kCFURLPOSIXPathStyle, false);

CFStringRef type = kUTTypePNG; // or kUTTypeBMP if you like
CGImageDestinationRef dest = CGImageDestinationCreateWithURL(url, type, 1, 0);

CGImageDestinationAddImage(dest, cgImage, 0);

CFRelease(cgImage);
CFRelease(bitmapContext);
CGImageDestinationFinalize(dest);
free(rgba);

Rundown

nschmidt you are the best!!! you have so much knowledge in the graphic computing/processing field. – Tombstone

Thanks so much. I've been looking for a code like this for days! – Compliancy

can you help me here please – Fabiola

@Rundown I've been trying to adapt your answer for iOS so I can convert raw brightness values back to an UIImage and I think I'm close, but I can't quite figure it out. Here's my question in case you have some time to spare. Thanks! – Spadix

Answer 2

Borrowing from nschmidt's code to produce a familiar, if someone red-eyed image:

int width = 11;
int height = 8;

Byte r[8][11]={
    {000,000,255,000,000,000,000,000,255,000,000},
    {000,000,000,255,000,000,000,255,000,000,000},  
    {000,000,255,255,255,255,255,255,255,000,000},
    {000,255,255,255,255,255,255,255,255,255,000},
    {255,255,255,255,255,255,255,255,255,255,255},
    {255,000,255,255,255,255,255,255,255,000,255},
    {255,000,255,000,000,000,000,000,255,000,255},
    {000,000,000,255,255,000,255,255,000,000,000}};

Byte g[8][11]={
    {000,000,255,000,000,000,000,000,255,000,000},
    {000,000,000,255,000,000,000,255,000,000,000},  
    {000,000,255,255,255,255,255,255,255,000,000},
    {000,255,255,000,255,255,255,000,255,255,000},
    {255,255,255,255,255,255,255,255,255,255,255},
    {255,000,255,255,255,255,255,255,255,000,255},
    {255,000,255,000,000,000,000,000,255,000,255},
    {000,000,000,255,255,000,255,255,000,000,000}};

Byte b[8][11]={
    {000,000,255,000,000,000,000,000,255,000,000},
    {000,000,000,255,000,000,000,255,000,000,000},  
    {000,000,255,255,255,255,255,255,255,000,000},
    {000,255,255,000,255,255,255,000,255,255,000},
    {255,255,255,255,255,255,255,255,255,255,255},
    {255,000,255,255,255,255,255,255,255,000,255},
    {255,000,255,000,000,000,000,000,255,000,255},
    {000,000,000,255,255,000,255,255,000,000,000}};

char* rgba = (char*)malloc(width*height*4);
int offset=0;
for(int i=0; i < height; ++i) 
{
    for (int j=0; j < width; j++) 
    {
        rgba[4*offset]   = r[i][j];
        rgba[4*offset+1] = g[i][j];
        rgba[4*offset+2] = b[i][j];
        rgba[4*offset+3] = 0;
        offset ++;
    }
}


CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef bitmapContext = CGBitmapContextCreate(
                                                   rgba,
                                                   width,
                                                   height,
                                                   8, // bitsPerComponent
                                                   4*width, // bytesPerRow
                                                   colorSpace,
                                                   kCGImageAlphaNoneSkipLast);

CFRelease(colorSpace);

CGImageRef cgImage = CGBitmapContextCreateImage(bitmapContext);

free(rgba);

UIImage *newUIImage = [UIImage imageWithCGImage:cgImage];

UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake(10, 10, 11,8)];

[iv setImage:newUIImage];

Then, addSubview:iv to get the image into your view and, of course, do the obligatory [releases] to keep a clean house.

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