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Class PegQuant

PegQuant is a run-time histogram and optimal palette producer. PegQuant implements a form of Heckbert's Median Cut color reduction algorithm. This class is only required for applications that must determine dynamic optimal palettes. Most applications run with fixed palettes. PegQuant is passed to PegImageConvert derived classes to create a histogram of color usage. After all included images have been added, the PegQuant function ReduceColors is called to create an optimal palette for use with the scanned images.

typedef  struct {        // structure for a cube in color space 
   PEGUINT   lower;         // one corner's index in histogram 
   PEGUINT   upper;         // another corner's index in histogram 
   DWORD  count;         // cube's histogram count 
   LONG   level;         // cube's level 
   UCHAR  rmin, rmax; 
   UCHAR  gmin, gmax; 
   UCHAR  bmin, bmax; 
} cube_t; 

typedef struct { 
   UCHAR    Blue; 
   UCHAR    Green; 
   UCHAR    Red; 
   UCHAR    Count; 
} PalEntry; 

class PegQuant 
{ 
   public: 
      PegQuant(); 
      void AddColor(PegPixel Pixel); 
      PEGUINT ReduceColors(PEGINT iLimit = 254); 
      UCHAR * GetPalette(void); 
      PEGUINT PalSize(void); 

   protected: 
      PEGUINT MedianCut(void); 
      void Shrink(cube_t * Cube); 
      void InvMap(LONG ncubes); 
      UCHAR GetNewIndex(LONG index); 
      LONG LookupPalIndex(UCHAR Red, UCHAR Green, UCHAR Blue); 
      cube_t mCubes[MAXCOLORS]; 
      LONG longdim; 
      PEGUINT * mpHistPtr; 
      PEGUINT * mpHist; 
      UCHAR ColMap[256][4]; 
      PEGINT miMaxColors; 
      PEGUINT miStartIndex; 
      PEGUINT miEndIndex; 
      UCHAR mPalette[256*3]; 
      LONG mlPalSize; 
};

Constructors

Creates a PegQuant object.

Method AddColor

This function adds the specified color to the histogram being created.

Method GetPalette

Returns a pointer to the optimal color palette produced from the image color sums.

Method PalSize

This function returns the current number of colors in the palette.

Method ReduceColors

This function is called after all colors for all images have been counted. This function actually does the work of creating the optimal palette for use with the images counted.

Examples

The following example reads several graphic files and creates an optimal palette for use in displaying the files. The palette is then installed as the new system palette.

#define GIF1 "c:\\graphics\\tree.gif" 
#define GIF2 "c:\\graphics\\house.gif" 
#define BMP1 "c:\\graphics\\garage.bmp" 

void CountColors(char * cPathName, PEGUINT wType, PegQuant * pQuant) 
{ 
   FILE * fSrc = fopen(cPathName, "r"); 
   PegImageConvert * pConvert; 

   if (wType == PIC_TYPE_GIF) 
      pConvert = new PegGifConvert(0); 
   else 
      pConvert = new PegBmpConvert(0); 

   pConvert->ReadImage(fSrc); 
   pConvert->CountColors(pQuant); 
   pConvert->DestroyImages(); 
   delete pConvert; 

   fclose(fSrc); 
} 

void CreatePalette(void) 
{ 
   PegQuant * pQuant = new PegQuant(); 

   CountColors(GIF1, PIC_TYPE_GIF, pQuant); 
   CountColors(GIF2, PIC_TYPE_GIF, pQuant); 
   CountColors(BMP1, PIC_TYPE_BMP, pQuant); 

   PEGUINT wPalSize =  pQuant->ReduceColors(); 
   Screen()->SetPalette(0, wPalSize, pQuant->GetPalette()); 

   delete pQuant; 
}

Class PegPngConvert