#import "GPUImageNobleCornerDetectionFilter.h"
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@implementation GPUImageNobleCornerDetectionFilter
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#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
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NSString *const kGPUImageNobleCornerDetectionFragmentShaderString = SHADER_STRING
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(
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varying highp vec2 textureCoordinate;
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uniform sampler2D inputImageTexture;
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uniform lowp float sensitivity;
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void main()
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{
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mediump vec3 derivativeElements = texture2D(inputImageTexture, textureCoordinate).rgb;
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mediump float derivativeSum = derivativeElements.x + derivativeElements.y;
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// R = (Ix^2 * Iy^2 - Ixy * Ixy) / (Ix^2 + Iy^2)
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mediump float zElement = (derivativeElements.z * 2.0) - 1.0;
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// mediump float harrisIntensity = (derivativeElements.x * derivativeElements.y - (derivativeElements.z * derivativeElements.z)) / (derivativeSum);
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mediump float cornerness = (derivativeElements.x * derivativeElements.y - (zElement * zElement)) / (derivativeSum);
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// Original Harris detector
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// R = Ix^2 * Iy^2 - Ixy * Ixy - k * (Ix^2 + Iy^2)^2
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// highp float harrisIntensity = derivativeElements.x * derivativeElements.y - (derivativeElements.z * derivativeElements.z) - harrisConstant * derivativeSum * derivativeSum;
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// gl_FragColor = vec4(vec3(harrisIntensity * 7.0), 1.0);
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gl_FragColor = vec4(vec3(cornerness * sensitivity), 1.0);
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}
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);
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#else
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NSString *const kGPUImageNobleCornerDetectionFragmentShaderString = 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 sensitivity;
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void main()
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{
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vec3 derivativeElements = texture2D(inputImageTexture, textureCoordinate).rgb;
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float derivativeSum = derivativeElements.x + derivativeElements.y;
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// R = (Ix^2 * Iy^2 - Ixy * Ixy) / (Ix^2 + Iy^2)
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float zElement = (derivativeElements.z * 2.0) - 1.0;
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// mediump float harrisIntensity = (derivativeElements.x * derivativeElements.y - (derivativeElements.z * derivativeElements.z)) / (derivativeSum);
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float cornerness = (derivativeElements.x * derivativeElements.y - (zElement * zElement)) / (derivativeSum);
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// Original Harris detector
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// R = Ix^2 * Iy^2 - Ixy * Ixy - k * (Ix^2 + Iy^2)^2
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// highp float harrisIntensity = derivativeElements.x * derivativeElements.y - (derivativeElements.z * derivativeElements.z) - harrisConstant * derivativeSum * derivativeSum;
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// gl_FragColor = vec4(vec3(harrisIntensity * 7.0), 1.0);
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gl_FragColor = vec4(vec3(cornerness * sensitivity), 1.0);
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}
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);
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#endif
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#pragma mark -
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#pragma mark Initialization and teardown
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- (id)init;
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{
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if (!(self = [self initWithCornerDetectionFragmentShader:kGPUImageNobleCornerDetectionFragmentShaderString]))
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{
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return nil;
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}
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return self;
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}
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@end
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