IOS OpenGL ES GPUImage 图像显示亮度最高的像素,其他为黑 GPUImageNonMaximumSuppressionFilte

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一.简介
二.效果演示
三.源码下载
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一.简介

GPUImage 共 125 个滤镜, 分为四类

1、Color adjustments : 31 filters , 颜色处理相关
2、Image processing : 40 filters , 图像处理相关.
3、Blending modes : 29 filters , 混合模式相关.
4、Visual effects : 25 filters , 视觉效果相关.

GPUImageNonMaximumSuppressionFilter 属于 GPUImage 图像视觉效果相关，用来处理**图像图像显示亮度最高的像素,其他为黑效果**。shader 源码如下：

/******************************************************************************************/
//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OpenGL ES GPUImage 图像显示亮度最高的像素,其他为黑 GPUImageNonMaximumSuppressionFilter
//@Time:2022/06/21 06:30
//@Motto:不积跬步无以至千里，不积小流无以成江海，程序人生的精彩需要坚持不懈地积累！
/******************************************************************************************/


#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageNonMaximumSuppressionFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;

 varying highp vec2 textureCoordinate;
 varying highp vec2 leftTextureCoordinate;
 varying highp vec2 rightTextureCoordinate;

 varying highp vec2 topTextureCoordinate;
 varying highp vec2 topLeftTextureCoordinate;
 varying highp vec2 topRightTextureCoordinate;

 varying highp vec2 bottomTextureCoordinate;
 varying highp vec2 bottomLeftTextureCoordinate;
 varying highp vec2 bottomRightTextureCoordinate;

 void main()
 {
     lowp float bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     lowp float bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     lowp float bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     lowp vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     lowp float leftColor = texture2D(inputImageTexture, leftTextureCoordinate).r;
     lowp float rightColor = texture2D(inputImageTexture, rightTextureCoordinate).r;
     lowp float topColor = texture2D(inputImageTexture, topTextureCoordinate).r;
     lowp float topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     lowp float topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).r;

     // Use a tiebreaker for pixels to the left and immediately above this one
     lowp float multiplier = 1.0 - step(centerColor.r, topColor);
     multiplier = multiplier * (1.0 - step(centerColor.r, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, bottomLeftColor));

     lowp float maxValue = max(centerColor.r, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);

     gl_FragColor = vec4((centerColor.rgb * step(maxValue, centerColor.r) * multiplier), 1.0);
 }
);
#else
NSString *const kGPUImageNonMaximumSuppressionFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;

 varying vec2 textureCoordinate;
 varying vec2 leftTextureCoordinate;
 varying vec2 rightTextureCoordinate;

 varying vec2 topTextureCoordinate;
 varying vec2 topLeftTextureCoordinate;
 varying vec2 topRightTextureCoordinate;

 varying vec2 bottomTextureCoordinate;
 varying vec2 bottomLeftTextureCoordinate;
 varying vec2 bottomRightTextureCoordinate;

 void main()
 {
     float bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     float bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     float bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     float leftColor = texture2D(inputImageTexture, leftTextureCoordinate).r;
     float rightColor = texture2D(inputImageTexture, rightTextureCoordinate).r;
     float topColor = texture2D(inputImageTexture, topTextureCoordinate).r;
     float topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     float topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).r;

     // Use a tiebreaker for pixels to the left and immediately above this one
     float multiplier = 1.0 - step(centerColor.r, topColor);
     multiplier = multiplier * (1.0 - step(centerColor.r, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, bottomLeftColor));

     float maxValue = max(centerColor.r, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);

     gl_FragColor = vec4((centerColor.rgb * step(maxValue, centerColor.r) * multiplier), 1.0);
 }
);
#endif