I am trying to get an interpolation of one color to another shade of the same color. (for eg: sky blue to dark blue and then back).
I stumbled upon some code that could be used if the range was from 0-255 or 0-1. However, in my case, I have the RGB codes for Color1 and Color2, and want the rotation to occur.
Color 1: 151,206,255
Color 2: 114,127,157
Any ideas how to go about this?
I suggest you convert RGB to HSV, then adjust its components, then convert back to RGB.
Wikipedia has an article about it, and it's been discussed here before:
Algorithm to convert RGB to HSV and HSV to RGB in range 0-255 for both
Also many frameworks have conversion functions, for example Qt has QColor class.
But the question was about the actual interpolation... here's a trivial interpolation function:
// 0 <= stepNumber <= lastStepNumber
int interpolate(int startValue, int endValue, int stepNumber, int lastStepNumber)
{
return (endValue - startValue) * stepNumber / lastStepNumber + startValue;
}
So call that for all color components you want to interpolate, in a loop. With RBG interpolation, you need to interpolate every component, in some other color space you may need to interpolate just one.
I know this is little bit old, but is worthy if someone is searching for it.
First of all, you can do interpolation in any color space, including RGB, which, in my opinion, is one of the easiest.
Let's assume the variation will be controlled by a fraction value between 0 and 1 (e.g. 0.3), where 0 means full color1 and 1 means full color2.
The theory:
Result = (color2 - color1) * fraction + color1
Applying:
As the RGB has 3 channels (red, green and blue) we have to perform this math for each one of the channels.
Using your example colors:
fraction: 0.3
color1: 151,206,255
color2: 114,127,157
R = (114-151) * fraction + 151
G = (127-206) * fraction + 206
B = (157-255) * fraction + 255
Code example in C/C++:
/**
* interpolate 2 RGB colors
* @param color1 integer containing color as 0x00RRGGBB
* @param color2 integer containing color as 0x00RRGGBB
* @param fraction how much interpolation (0..1)
* - 0: full color 1
* - 1: full color 2
* @return the new color after interpolation
*/
int interpolate(int color1, int color2, float fraction)
{
unsigned char r1 = (color1 >> 16) & 0xff;
unsigned char r2 = (color2 >> 16) & 0xff;
unsigned char g1 = (color1 >> 8) & 0xff;
unsigned char g2 = (color2 >> 8) & 0xff;
unsigned char b1 = color1 & 0xff;
unsigned char b2 = color2 & 0xff;
return (int) ((r2 - r1) * fraction + r1) << 16 |
(int) ((g2 - g1) * fraction + g1) << 8 |
(int) ((b2 - b1) * fraction + b1);
}
/*
* 0x0097ceff == RGB(151,206,255)
* 0x00727f9d == RGB(114,127,157)
*/
int new_color = interpolate(0x0097ceff, 0x00727f9d, 0.3f);
EDIT 1.
As pointed out by flying sheep, the RGB format may introduce some undesired colors during a blend operation. To solve this problem new steps may be added to the process: convert to linear RGB, perform the interpolation and then convert it back. Below a working example in C that also generates a PPM file for visualization.
/* vim: set sw=4 ts=4 nowrap hlsearch: */
#include <stdio.h>
#include <math.h>
#include <inttypes.h>
/**
* convert a single default RGB (a.k.a. sRGB) channel to linear RGB
* @param channel R, G or B channel
* @return channel in linear RGB
*/
float rgb2linear(uint8_t channel)
{
float s = channel / 255.0f;
return s <= 0.04045 ? s / 12.92 : pow((s + 0.055) / 1.055, 2.4);
}
/**
* convert a linear RGB channel to default RGB channel (a.k.a. sRGB)
* @param linear R, G or B channel in linear format
* @return converted channel to default RGB value
*/
uint8_t linear2rgb(float linear)
{
float s = linear <= 0.0031308 ? linear * 12.92 : 1.055 * pow(linear, 1.0/2.4) - 0.055;
return (uint8_t) (s * 255);
}
/**
* interpolate 2 RGB colors
* @param color1 integer containing color as 0x00RRGGBB
* @param color2 integer containing color as 0x00RRGGBB
* @param fraction how much interpolation (0..1)
* - 0: full color 1
* - 1: full color 2
* @return the new color after interpolation
*/
int interpolate(int color1, int color2, float fraction)
{
uint8_t in[3];
for(int x = 0; x < 3; x++) {
float c1 = rgb2linear((color1 >> (16 - x * 8)) & 0xff);
float c2 = rgb2linear((color2 >> (16 - x * 8)) & 0xff);
in[x] = linear2rgb((c2 - c1) * fraction + c1);
}
return in[0] << 16 | in[1] << 8 | in[2];;
}
/**
* example interpolating sRGB colors
* first the colors are converted to linear-RGB,
* interpolated and then converted back to sRGB
*/
int main(int argc, char *argv[])
{
float factor = 0.3f;
int c1 = 0x0097ceff; /* RGB(151,206,255) */
int c2 = 0x00727f9d; /* RGB(114,127,157) */
int nc = interpolate(c1, c2, factor);
printf("interpolate 0x%08x to 0x%08x ==> 0x%08x factor: %.2f\n", c1, c2, nc, factor);
/* create a PPM file to vizualize the interpolation
* gradients in 100 steps - PPM files may be opened
* in Gimp or other image editors */
FILE *f = fopen("interpolate.ppm", "w");
if(f) {
/* PPM file header */
fprintf(f, "P3\n");
fprintf(f, "707 50\n");
fprintf(f, "255\n");
/* iterate over the rows */
for(int x = 0; x < 50; x++) {
/* iterate over the steps */
for(int k = 0; k <= 100; k++) {
factor = k * 0.01f;
nc = interpolate(c1, c2, factor);
/* iterate over the cols */
for(int y = 0; y < 7; y++) {
fprintf(f, "%d %d %d%s", (nc >> 16) & 0xff, (nc >> 8) & 0xff, nc & 0xff, k+1 > 100 && y+1 >= 7 ? "\n" : " ");
}
}
}
fclose(f);
}
return 0;
}
PPM image:
I suggest you convert RGB to HSV, then adjust its components, then convert back to RGB.
Wikipedia has an article about it, and it's been discussed here before:
Algorithm to convert RGB to HSV and HSV to RGB in range 0-255 for both
Also many frameworks have conversion functions, for example Qt has QColor class.
But the question was about the actual interpolation... here's a trivial interpolation function:
// 0 <= stepNumber <= lastStepNumber
int interpolate(int startValue, int endValue, int stepNumber, int lastStepNumber)
{
return (endValue - startValue) * stepNumber / lastStepNumber + startValue;
}
So call that for all color components you want to interpolate, in a loop. With RBG interpolation, you need to interpolate every component, in some other color space you may need to interpolate just one.
Convert your RGB colors to HSV then interpolate each component (not only the color, see end of answer), afterwards you can convert back to RGB.
You can do RGB interpolation, but the results are better with HSV, because in this space color is separated from luminance and saturation (Wikipedia article on HSV). HSV interpolation is more "logical" than the RGB one, because with the latter you can get extra colors while interpolating.
Some code for interpolation:
template<typename F>
ColorRGB interpolate(ColorRGB a, ColorRGB b, float t, F interpolator)
{
// 0.0 <= t <= 1.0
ColorHSV ca = convertRGB2HSV(a);
ColorHSV cb = convertRGB2HSV(b);
ColorHSV final;
final.h = interpolator(ca.h, cb.h, t);
final.s = interpolator(ca.s, cb.s, t);
final.v = interpolator(ca.v, cb.v, t);
return convertHSV2RGB(final);
}
int linear(int a, int b, float t)
{
return a * (1 - t) + b * t;
}
// use: result = interpolate(color1,color2,ratio,&linear);
linear() HSV interpolation shown will sometimes add a range of hues, as it doesn't take into account that hue is cyclical. Going from red (at 0 degrees) to violet (at 300) will produce orange, yellow, green, blue--almost the whole spectrum--when you'd probably want to normalize and take the shorter route through violet. –
Gigue The best color space to use for visual effects is HCL. This is a space created specifically to look good while traversing its dimension, where "look good" does not relate to any physical properties of light or ink, like RGB and CMYK respectively.
Using HCL is expensive so the best thing to do is to create a number of intermediary values in this space and then interpolate in RGB which is native. This is what I have done in my animation engine.
Here is a snippet from it, in Swift 4.0
extension UIColor {
typealias Components = (CGFloat, CGFloat, CGFloat, CGFloat)
enum Space: String {
case RGB = "RGB"
case HSB = "HSB"
case HCL = "HCL"
}
func components(in space: UIColor.Space) -> Components {
switch space {
case .RGB: return self.rgba // var defined in HandyUIKit's extension
case .HSB: return self.hsba // var defined in HandyUIKit's extension
case .HCL: return self.hlca // var defined in HandyUIKit's extension
}
}
func spectrum(to tcol: UIColor, for space: UIColor.Space) -> [UIColor] {
var spectrum = [UIColor]()
spectrum.append(self)
let fcomps = self.components(in: space)
let tcomps = tcol.components(in: space)
for i in 0 ... 5 {
let factor = CGFloat(i) / 5.0
let comps = (1.0 - factor) * fcomps + factor * tcomps
let color = UIColor(with: comps, in: space)
spectrum.append(color)
}
spectrum.append(tcol)
return spectrum
}
convenience init(with components: Components, in space: Space) {
switch space {
case .RGB: self.init(red: components.0, green: components.1, blue: components.2, alpha: components.3)
case .HSB: self.init(hue: components.0, saturation: components.1, brightness: components.2, alpha: components.3)
case .HCL: self.init(hue: components.0, luminance: components.1, chroma: components.2, alpha: components.3)
}
}
}
func *(lhs:CGFloat, rhs:UIColor.Components) -> UIColor.Components {
return (lhs * rhs.0, lhs * rhs.1, lhs * rhs.2, lhs * rhs.3)
}
func +(lhs:UIColor.Components, rhs:UIColor.Components) -> UIColor.Components {
return (lhs.0 + rhs.0, lhs.1 + rhs.1, lhs.2 + rhs.2, lhs.3 + rhs.3)
}
Both the engine and the example above are using HandyUIKit for the conversions between spaces so please add this project to whatever you are building for the code above to work.
I have written an article about it.
I see that you have tagged this question under "openframeworks" tag.
so all you need to do is use the method ofColor::getLerped or ofColor::lerp
getLerped returns new value, while lerp modifies the color.
for example:
ofColor c1(151,206,255);
ofColor c2(114,127,157);
float p = 0.2f;
ofColor c3 = c1.getLerped(c2, p);
or
c1.lerp(c2, 0.3f);
I have adapted Synxis's C example (above) into an executable JavaScript program.
The program interpolates the color yellow, from red and green. The input and output is in RGB-space, but the interpolation is handled in the HSV-space. I also added an RGB interpolation example. As you can see below, a dark-yellow is produced if you interpolate red and green in RGB-space.
/** Main */
var red = { r : 255, g : 0, b : 0 };
var green = { r : 0, g : 255, b : 0 };
var yellow = interpolateHsv(red, green, 0.5, linear);
var darkYellow = interpolateRgb(red, green, 0.5, linear);
document.body.innerHTML =
'Yellow: ' + JSON.stringify(yellow, null, ' ') + '<br />' +
'Dark Yellow: ' + JSON.stringify(darkYellow, null, ' ');
/**
* Returns an HSV interpolated value between two rgb values.
*
* @param {Object} rgbA - rgb() tuple
* @param {Object} rgbB - rgb() tuple
* @param {Number} threshold - float between [0.0, 1.0]
* @param {function} interpolatorFn - interpolator function
* @return {Object} rbg
*/
function interpolateHsv(rgbA, rgbB, threshold, interpolatorFn) {
var hsvA = rgbToHsv(rgbA);
var hsvB = rgbToHsv(rgbB);
threshold = toArray(threshold, 3);
return hsvToRgb({
h : interpolatorFn(hsvA.h, hsvB.h, threshold[0]),
s : interpolatorFn(hsvA.s, hsvB.s, threshold[1]),
v : interpolatorFn(hsvA.v, hsvB.v, threshold[2])
});
}
/**
* Returns an RGB interpolated value between two rgb values.
*
* @param {Object} rgbA - rgb() tuple
* @param {Object} rgbB - rgb() tuple
* @param {Number} threshold - float between [0.0, 1.0]
* @param {function} interpolatorFn - interpolator function
* @return {Object} rbg
*/
function interpolateRgb(rgbA, rgbB, threshold, interpolatorFn) {
threshold = toArray(threshold, 3);
return {
r : ~~interpolatorFn(rgbA.r, rgbB.r, threshold[0]),
g : ~~interpolatorFn(rgbA.g, rgbB.g, threshold[1]),
b : ~~interpolatorFn(rgbA.b, rgbB.b, threshold[2])
};
}
/**
* Returns an interpolated value between two values.
*
* @param {Number} valueA - color channel int value
* @param {Number} valueB - color channel int value
* @param {Number} threshold - float between [0.0, 1.0]
* @param {function} interpolatorFn - interpolator function
* @return {int}
*/
function linear(valueA, valueB, threshold) {
return valueA * (1 - threshold) + valueB * threshold;
}
/**
* Converts an RGB color value to HSV. Conversion formula
* adapted from http://en.wikipedia.org/wiki/HSV_color_space.
* Assumes r, g, and b are contained in the set [0, 255] and
* returns h, s, and v in the set [0, 1].
*
* @param {Object} rgb - Color in rgb mode
* @return {Object} - Color in hsv mode
*/
function rgbToHsv(rgb) {
var r = rgb.r / 255,
g = rgb.g / 255,
b = rgb.b / 255;
var max = Math.max(r, g, b), min = Math.min(r, g, b);
var h, s, v = max;
var d = max - min;
s = max === 0 ? 0 : d / max;
if (max == min) {
h = 0; // achromatic
} else {
switch(max) {
case r: h = (g - b) / d + (g < b ? 6 : 0); break;
case g: h = (b - r) / d + 2; break;
case b: h = (r - g) / d + 4; break;
}
h /= 6;
}
return {
h : h,
s : s,
v : v
};
}
/**
* Converts an HSV color value to RGB. Conversion formula
* adapted from http://en.wikipedia.org/wiki/HSV_color_space.
* Assumes h, s, and v are contained in the set [0, 1] and
* returns r, g, and b in the set [0, 255].
*
* @param {Object} hsv - Color in hsv mode
* @return {Object} - Color in rgb mode
*/
function hsvToRgb(hsv){
var r, g, b, i, f, p, q, t,
h = hsv.h,
s = hsv.s,
v = hsv.v;
i = Math.floor(h * 6);
f = h * 6 - i;
p = v * (1 - s);
q = v * (1 - f * s);
t = v * (1 - (1 - f) * s);
switch(i % 6){
case 0: r = v, g = t, b = p; break;
case 1: r = q, g = v, b = p; break;
case 2: r = p, g = v, b = t; break;
case 3: r = p, g = q, b = v; break;
case 4: r = t, g = p, b = v; break;
case 5: r = v, g = p, b = q; break;
}
return {
r : r * 255,
g : g * 255,
b : b * 255
};
}
function isNumeric(n) {
return !isNaN(parseFloat(n)) && isFinite(n);
}
function toArray(arr, size) {
var isNum = isNumeric(arr);
arr = !Array.isArray(arr) ? [arr] : arr;
for (var i = 1; i < size; i++) {
if (arr.length < size) {
arr.push(isNum ? arr[0] : 0);
}
}
return arr;
}Here's a Swift 2 version based on @hyde's answer:
import UIKit
func interpolate(start start: CGFloat, end: CGFloat, progress: CGFloat) -> CGFloat {
return (end - start) * progress + start
}
extension UIColor {
func interpolateTo(color end: UIColor, progress: CGFloat) -> UIColor {
var r1: CGFloat = 0
var g1: CGFloat = 0
var b1: CGFloat = 0
var a1: CGFloat = 0
getRed(&r1, green: &g1, blue: &b1, alpha: &a1)
var r2: CGFloat = 0
var g2: CGFloat = 0
var b2: CGFloat = 0
var a2: CGFloat = 0
end.getRed(&r2, green: &g2, blue: &b2, alpha: &a2)
return UIColor(
red: interpolate(start: r1, end: r2, progress: progress),
green: interpolate(start: g1, end: g2, progress: progress),
blue: interpolate(start: b1, end: b2, progress: progress),
alpha: interpolate(start: a1, end: a2, progress: progress)
)
}
}
You can use it like this:
color1.interpolateTo(color: color2, progress: t)
Where t is the percentage (0-1) of your interpolation.
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