IOS – OpenGL ES 桑原濾波/水粉畫模糊效果 GPUImageKuwaharaFilter_猿說程式設計

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一.簡介

GPUImage 共 125 個濾鏡, 分為四類

1、Color adjustments : 31 filters , 顏色處理相關
2、Image processing : 40 filters , 影象處理相關.
3、Blending modes : 29 filters , 混合模式相關.
4、Visual effects : 25 filters , 視覺效果相關.

GPUImageKuwaharaFilter GPUImage 影象桑原濾波/水粉畫模糊效果，shader 原始碼如下：

/******************************************************************************************/
//@Author:猿說程式設計
//@Blog(個人部落格地址): www.codersrc.com
//@File:IOS – OpenGL ES 桑原濾波/水粉畫模糊效果 GPUImageKuwaharaFilter
//@Time:2022/05/15 10:30
//@Motto:不積跬步無以至千里，不積小流無以成江海，程式人生的精彩需要堅持不懈地積累！
/******************************************************************************************/
#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageKuwaharaFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;
 uniform int radius;

 precision highp float;

 const vec2 src_size = vec2 (1.0 / 768.0, 1.0 / 1024.0);

 void main (void)
 {
     vec2 uv = textureCoordinate;
     float n = float((radius + 1) * (radius + 1));
     int i; int j;
     vec3 m0 = vec3(0.0); vec3 m1 = vec3(0.0); vec3 m2 = vec3(0.0); vec3 m3 = vec3(0.0);
     vec3 s0 = vec3(0.0); vec3 s1 = vec3(0.0); vec3 s2 = vec3(0.0); vec3 s3 = vec3(0.0);
     vec3 c;

     for (j = -radius; j <= 0; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m0 += c;
             s0 += c * c;
         }
     }

     for (j = -radius; j <= 0; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m1 += c;
             s1 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m2 += c;
             s2 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m3 += c;
             s3 += c * c;
         }
     }


     float min_sigma2 = 1e+2;
     m0 /= n;
     s0 = abs(s0 / n - m0 * m0);

     float sigma2 = s0.r + s0.g + s0.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m0, 1.0);
     }

     m1 /= n;
     s1 = abs(s1 / n - m1 * m1);

     sigma2 = s1.r + s1.g + s1.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m1, 1.0);
     }

     m2 /= n;
     s2 = abs(s2 / n - m2 * m2);

     sigma2 = s2.r + s2.g + s2.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m2, 1.0);
     }

     m3 /= n;
     s3 = abs(s3 / n - m3 * m3);

     sigma2 = s3.r + s3.g + s3.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m3, 1.0);
     }
 }
);
#else
NSString *const kGPUImageKuwaharaFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;
 uniform int radius;

 const vec2 src_size = vec2 (1.0 / 768.0, 1.0 / 1024.0);

 void main (void)
 {
     vec2 uv = textureCoordinate;
     float n = float((radius + 1) * (radius + 1));
     int i; int j;
     vec3 m0 = vec3(0.0); vec3 m1 = vec3(0.0); vec3 m2 = vec3(0.0); vec3 m3 = vec3(0.0);
     vec3 s0 = vec3(0.0); vec3 s1 = vec3(0.0); vec3 s2 = vec3(0.0); vec3 s3 = vec3(0.0);
     vec3 c;

     for (j = -radius; j <= 0; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m0 += c;
             s0 += c * c;
         }
     }

     for (j = -radius; j <= 0; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m1 += c;
             s1 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m2 += c;
             s2 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m3 += c;
             s3 += c * c;
         }
     }


     float min_sigma2 = 1e+2;
     m0 /= n;
     s0 = abs(s0 / n - m0 * m0);

     float sigma2 = s0.r + s0.g + s0.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m0, 1.0);
     }

     m1 /= n;
     s1 = abs(s1 / n - m1 * m1);

     sigma2 = s1.r + s1.g + s1.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m1, 1.0);
     }

     m2 /= n;
     s2 = abs(s2 / n - m2 * m2);

     sigma2 = s2.r + s2.g + s2.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m2, 1.0);
     }

     m3 /= n;
     s3 = abs(s3 / n - m3 * m3);

     sigma2 = s3.r + s3.g + s3.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m3, 1.0);
     }
 }
);
#endif

二.效果演示

使用 GPUImageKuwaharaFilter** ** 用來影象卡通效果（黑色粗線描邊），原圖：

**GPUImageKuwaharaFilter** 用來影象卡通效果（黑色粗線描邊），效果圖：

三.原始碼下載

OpenGL ES Demo 下載地址 : IOS – OpenGL ES 桑原濾波/水粉畫模糊效果 GPUImageKuwaharaFilter

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