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#import "GPUImageHueFilter.h"
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// Adapted from http://stackoverflow.com/questions/9234724/how-to-change-hue-of-a-texture-with-glsl - see for code and discussion
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#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
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NSString *const kGPUImageHueFragmentShaderString = SHADER_STRING
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(
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precision highp float;
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varying highp vec2 textureCoordinate;
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uniform sampler2D inputImageTexture;
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uniform mediump float hueAdjust;
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const highp vec4 kRGBToYPrime = vec4 (0.299, 0.587, 0.114, 0.0);
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const highp vec4 kRGBToI = vec4 (0.595716, -0.274453, -0.321263, 0.0);
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const highp vec4 kRGBToQ = vec4 (0.211456, -0.522591, 0.31135, 0.0);
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const highp vec4 kYIQToR = vec4 (1.0, 0.9563, 0.6210, 0.0);
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const highp vec4 kYIQToG = vec4 (1.0, -0.2721, -0.6474, 0.0);
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const highp vec4 kYIQToB = vec4 (1.0, -1.1070, 1.7046, 0.0);
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void main ()
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{
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// Sample the input pixel
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highp vec4 color = texture2D(inputImageTexture, textureCoordinate);
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// Convert to YIQ
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highp float YPrime = dot (color, kRGBToYPrime);
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highp float I = dot (color, kRGBToI);
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highp float Q = dot (color, kRGBToQ);
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// Calculate the hue and chroma
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highp float hue = atan (Q, I);
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highp float chroma = sqrt (I * I + Q * Q);
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// Make the user's adjustments
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hue += (-hueAdjust); //why negative rotation?
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// Convert back to YIQ
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Q = chroma * sin (hue);
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I = chroma * cos (hue);
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// Convert back to RGB
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highp vec4 yIQ = vec4 (YPrime, I, Q, 0.0);
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color.r = dot (yIQ, kYIQToR);
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color.g = dot (yIQ, kYIQToG);
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color.b = dot (yIQ, kYIQToB);
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// Save the result
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gl_FragColor = color;
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}
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);
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#else
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NSString *const kGPUImageHueFragmentShaderString = SHADER_STRING
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(
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varying vec2 textureCoordinate;
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uniform sampler2D inputImageTexture;
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uniform float hueAdjust;
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const vec4 kRGBToYPrime = vec4 (0.299, 0.587, 0.114, 0.0);
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const vec4 kRGBToI = vec4 (0.595716, -0.274453, -0.321263, 0.0);
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const vec4 kRGBToQ = vec4 (0.211456, -0.522591, 0.31135, 0.0);
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const vec4 kYIQToR = vec4 (1.0, 0.9563, 0.6210, 0.0);
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const vec4 kYIQToG = vec4 (1.0, -0.2721, -0.6474, 0.0);
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const vec4 kYIQToB = vec4 (1.0, -1.1070, 1.7046, 0.0);
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void main ()
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{
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// Sample the input pixel
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vec4 color = texture2D(inputImageTexture, textureCoordinate);
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// Convert to YIQ
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float YPrime = dot (color, kRGBToYPrime);
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float I = dot (color, kRGBToI);
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float Q = dot (color, kRGBToQ);
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// Calculate the hue and chroma
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float hue = atan (Q, I);
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float chroma = sqrt (I * I + Q * Q);
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// Make the user's adjustments
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hue += (-hueAdjust); //why negative rotation?
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// Convert back to YIQ
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Q = chroma * sin (hue);
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I = chroma * cos (hue);
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// Convert back to RGB
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vec4 yIQ = vec4 (YPrime, I, Q, 0.0);
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color.r = dot (yIQ, kYIQToR);
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color.g = dot (yIQ, kYIQToG);
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color.b = dot (yIQ, kYIQToB);
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// Save the result
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gl_FragColor = color;
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}
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);
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#endif
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@implementation GPUImageHueFilter
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@synthesize hue;
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- (id)init
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{
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if(! (self = [super initWithFragmentShaderFromString:kGPUImageHueFragmentShaderString]) )
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{
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return nil;
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}
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hueAdjustUniform = [filterProgram uniformIndex:@"hueAdjust"];
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self.hue = 90;
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return self;
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}
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- (void)setHue:(CGFloat)newHue
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{
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// Convert degrees to radians for hue rotation
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hue = fmodf(newHue, 360.0) * M_PI/180;
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[self setFloat:hue forUniform:hueAdjustUniform program:filterProgram];
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}
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@end
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