CPUImageRGBFilter 实现

参考自: https://github.com/BradLarson/GPUImage

GPUImageRGBFilter: Adjusts the individual RGB channels of an image

• red: Normalized values by which each color channel is multiplied. The range is from 0.0 up, with 1.0 as the default.
• green:
• blue:

对应的Shader:

varying highp vec2 textureCoordinate;
 
 uniform sampler2D inputImageTexture;
 uniform highp float redAdjustment;
 uniform highp float greenAdjustment;
 uniform highp float blueAdjustment;
 
 void main()
 {
     highp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
 
     gl_FragColor = vec4(textureColor.r * redAdjustment, textureColor.g * greenAdjustment, textureColor.b * blueAdjustment, textureColor.a);
 }

简单解释一下以上Shader.

uniform 声明为只读变量。

varying 声明为读写变量。

highp 为计算精度。这里为高精度。

textureCoordinate为对应的纹理坐标位置即(x,y)

inputImageTexture为输入的纹理图。

texture2D 取对应纹理图所在坐标的像素颜色。

所以整个算法很简单，就是将对应纹理图所在坐标的像素进行相应的 红绿蓝 权重调整。
权重的取值范围为[0,1]

根据以上Shader进行CPU代码转换。

#ifndef ClampToByte
#define ClampToByte(v)(((unsigned) int(v)) < (255) ? (v) : (v < 0) ? int(0) : int(255))
#endif
 
void CPUImageRGBFilter(unsigned char* Input, unsigned char* Output, int  Width, int  Height, int Stride, float redAdjustment = 1.0f, float greenAdjustment = 1.0f, float blueAdjustment = 1.0f)
{
    int Channels = Stride / Width;
    )      return;
    int numberOfPixels = Width*Height;
    unsigned char* scanLineIn = Input;
    unsigned char* scanLineOut = Output;
    ; pixel < numberOfPixels; pixel++) {
        scanLineOut[] = ClampToByte(scanLineIn[] * redAdjustment);
        scanLineOut[] = ClampToByte(scanLineIn[] * greenAdjustment);
        scanLineOut[] = ClampToByte(scanLineIn[] * blueAdjustment);
        scanLineIn += Channels;
        scanLineOut += Channels;
    }
}

转换后可进行建表优化。

即:

void CPUImageRGBFilter(unsigned char* Input, unsigned char* Output, int  Width, int  Height, int Stride, float redAdjustment = 1.0f, float greenAdjustment = 1.0f, float blueAdjustment = 1.0f)
{
    int Channels = Stride / Width;
    )      return;
    unsigned ] = {  };
    unsigned ] = {  };
    unsigned ] = {  };
    ; pixel < ; pixel++)
    {
        AdjustMapR[pixel] = pixel*redAdjustment;
        AdjustMapG[pixel] = pixel*greenAdjustment;
        AdjustMapB[pixel] = pixel*blueAdjustment;
    }
    ; Y < Height; Y++)
    {
        unsigned char*     scanLineOut = Output + (Y * Stride);
        unsigned char*     scanLineIn = Input + (Y * Stride);
        ; X < Width; X++)
        {
            scanLineOut[] = AdjustMapR[scanLineIn[]];
            scanLineOut[] = AdjustMapG[scanLineIn[]];
            scanLineOut[] = AdjustMapB[scanLineIn[]];
            scanLineIn += Channels;
            scanLineOut += Channels;
        }
    }
}

代码比较简单，一看就明了。

待后续有时间，再通过simd指令集以及thread等方式进行改写。