RGB格式图像转化为HSV格式

注：在阴影检测算法中经常需要将RGB格式的图像转化为HSV格式，对于阴影区域而言，它的色度和饱和度相对于原图像而言变化不大，主要是亮度信息变化较大，，将RGB格式转化为HSV格式，就可以得到H、S、V分量，从而得到色度、饱和度、亮度得值；

转换程序：

void convert_ImageRGBtoHSV(const Mat& imageRGB, Mat &imageHSV)
{
 float fR, fG, fB;
 float fH, fS, fV;
 const float FLOAT_TO_BYTE = 255.0f;
 const float BYTE_TO_FLOAT = 1.0f / FLOAT_TO_BYTE;

 // Create a blank HSV image
 //if (!imageHSV || imageRGB->depth != 8 || imageRGB->nChannels != 3) {
 //printf("ERROR in convertImageRGBtoHSV()! Bad input image. ");
 //exit(1);
 //}

 int h = imageRGB.rows;  // Pixel height.
 int w = imageRGB.cols;  // Pixel width.
 //int rowSizeRGB = imageRGB->widthStep; // Size of row in bytes, including extra padding.
 //char *imRGB = imageRGB->imageData; // Pointer to the start of the image pixels.
 //int rowSizeHSV = imageHSV->widthStep; // Size of row in bytes, including extra padding.
 //char *imHSV = imageHSV->imageData; // Pointer to the start of the image pixels.
 for (int y = 0; y < h; ++y) {
  for (int x = 0; x < w; ++x) {
   // Get the RGB pixel components. NOTE that OpenCV stores RGB pixels in B,G,R order.
   //uchar *pRGB = (uchar*)(imRGB + y*rowSizeRGB + x*3);
   int bB = imageRGB.at<Vec3b>(y, x)[0]; //*(uchar*)(pRGB+0); // Blue component
   int bG = imageRGB.at<Vec3b>(y, x)[1]; //*(uchar*)(pRGB+1); // Green component
   int bR = imageRGB.at<Vec3b>(y, x)[2]; //*(uchar*)(pRGB+2); // Red component

   // Convert from 8-bit integers to floats.
   fR = bR * BYTE_TO_FLOAT;
   fG = bG * BYTE_TO_FLOAT;
   fB = bB * BYTE_TO_FLOAT;

   // Convert from RGB to HSV, using float ranges 0.0 to 1.0.
   float fDelta;
   float fMin, fMax;
   int iMax;
   // Get the min and max, but use integer comparisons for slight speedup.
   if (bB < bG) {
    if (bB < bR) {
     fMin = fB;
     if (bR > bG) {
      iMax = bR;
      fMax = fR;
     }
     else {
      iMax = bG;
      fMax = fG;
     }
    }
    else {
     fMin = fR;
     fMax = fG;
     iMax = bG;
    }
   }
   else {
    if (bG < bR) {
     fMin = fG;
     if (bB > bR) {
      fMax = fB;
      iMax = bB;
     }
     else {
      fMax = fR;
      iMax = bR;
     }
    }
    else {
     fMin = fR;
     fMax = fB;
     iMax = bB;
    }
   }
   fDelta = fMax - fMin;
   fV = fMax;    // Value (Brightness).
   if (iMax != 0) {   // Make sure its not pure black.
    fS = fDelta / fMax;  // Saturation.
    float ANGLE_TO_UNIT = 1.0f / (6.0f * fDelta); // Make the Hues between 0.0 to 1.0 instead of 6.0
    if (iMax == bR) {  // between yellow and magenta.
     fH = (fG - fB) * ANGLE_TO_UNIT;
    }
    else if (iMax == bG) {  // between cyan and yellow.
     fH = (2.0f / 6.0f) + (fB - fR) * ANGLE_TO_UNIT;
    }
    else {    // between magenta and cyan.
     fH = (4.0f / 6.0f) + (fR - fG) * ANGLE_TO_UNIT;
    }
    // Wrap outlier Hues around the circle.
    if (fH < 0.0f)
     fH += 1.0f;
    if (fH >= 1.0f)
     fH -= 1.0f;
   }
   else {
    // color is pure Black.
    fS = 0;
    fH = 0; // undefined hue
   }

   // Convert from floats to 8-bit integers.
   int bH = (int)(0.5f + fH * 255.0f);
   int bS = (int)(0.5f + fS * 255.0f);
   int bV = (int)(0.5f + fV * 255.0f);

   // Clip the values to make sure it fits within the 8bits.
   if (bH > 255)
    bH = 255;
   if (bH < 0)
    bH = 0;
   if (bS > 255)
    bS = 255;
   if (bS < 0)
    bS = 0;
   if (bV > 255)
    bV = 255;
   if (bV < 0)
    bV = 0;

   // Set the HSV pixel components.
   imageHSV.at<Vec3b>(y, x)[0] = bH;  // H component
   imageHSV.at<Vec3b>(y, x)[1] = bS;  // S component
   imageHSV.at<Vec3b>(y, x)[2] = bV;  // V component
  }
 }
}