色键 Chroma Key

整理下色键代码

ffmpeg 

typedef struct ColorkeyContext {
    const AVClass *class;

    /* color offsets rgba */
    int co[4];

    uint8_t colorkey_rgba[4];
    float similarity;
    float blend;
} ColorkeyContext;

static uint8_t do_colorkey_pixel(ColorkeyContext *ctx, uint8_t r, uint8_t g, uint8_t b)
{
    int dr = (int)r - ctx->colorkey_rgba[0];
    int dg = (int)g - ctx->colorkey_rgba[1];
    int db = (int)b - ctx->colorkey_rgba[2];

    double diff = sqrt((dr * dr + dg * dg + db * db) / (255.0 * 255.0));

    if (ctx->blend > 0.0001) {
        return av_clipd((diff - ctx->similarity) / ctx->blend, 0.0, 1.0) * 255.0;
    } else {
        return (diff > ctx->similarity) ? 255 : 0;
    }
}

gpuimage

// from: https://github.com/BradLarson/GPUImage/blob/master/framework/Source/GPUImageChromaKeyFilter.m

#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif

#define PROCESSING_TEXTURE_SHADER

uniform sampler2D texture;
varying vec4 vertColor;
varying vec4 vertTexCoord;

uniform float thresholdSensitivity;
uniform float smoothing;
uniform vec3 colorToReplace;

void main()
{
    vec4 textureColor = texture2D(texture, vertTexCoord.xy);
    
    float maskY = 0.2989 * colorToReplace.r + 0.5866 * colorToReplace.g + 0.1145 * colorToReplace.b;
    float maskCr = 0.7132 * (colorToReplace.r - maskY);
    float maskCb = 0.5647 * (colorToReplace.b - maskY);
    
    float Y = 0.2989 * textureColor.r + 0.5866 * textureColor.g + 0.1145 * textureColor.b;
    float Cr = 0.7132 * (textureColor.r - Y);
    float Cb = 0.5647 * (vertColor.b - Y);
    
    float blendValue = smoothstep(thresholdSensitivity, thresholdSensitivity + smoothing, distance(vec2(Cr, Cb), vec2(maskCr, maskCb)));
    gl_FragColor = vec4(textureColor.rgb, textureColor.a * blendValue);
}

http://gc-films.com/chromakey.html 

double colorclose(int Cb_p,int Cr_p,int Cb_key,int Cr_key,int tola,int tolb) 
{ 
   /*decides if a color is close to the specified hue*/ 
   double temp = sqrt((Cb_key-Cb_p)*(Cb_key-Cb_p)+(Cr_key-Cr_p)*(Cr_key-Cr_p)); 
   if (temp < tola) {return (0.0);} 
   if (temp < tolb) {return ((temp-tola)/(tolb-tola));} 
   return (1.0); 
} 

http://www.cs.utah.edu/~michael/chroma/

High Quality Chroma Key

这个代码我实现了一下 效果远远达不到要求 专业的摄像机效果好点

头发没法抠出来