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quantize.c

/*****************************************************************************
*   "Gif-Lib" - Yet another gif library.                         *
*                                                          *
* Written by:  Gershon Elber              IBM PC Ver 0.1,   Jun. 1989    *
******************************************************************************
* Module to quatize high resolution image into lower one. You may want to    *
* peek into the following article this code is based on:               *
* "Color Image Quantization for frame buffer Display", by Paul Heckbert      *
* SIGGRAPH 1982 page 297-307.                                    *
******************************************************************************
* History:                                                 *
* 5 Jan 90 - Version 1.0 by Gershon Elber.                             *
*****************************************************************************/

#ifdef __MSDOS__
#include <dos.h>
#include <alloc.h>
#include <graphics.h>
#endif /* __MSDOS__ */

#include <stdio.h>
#include <stdlib.h>
#include "gif_lib.h"

#define PROGRAM_NAME    "GIF_LIBRARY"

#define ABS(x)    ((x) > 0 ? (x) : (-(x)))

/* The colors are stripped to 5 bits per primary color if non MSDOS system  */
/* or to 4 (not enough memory...) if MSDOS as first step.             */
#ifdef __MSDOS__
#define COLOR_ARRAY_SIZE 4096
#define BITS_PER_PRIM_COLOR 4
#define MAX_PRIM_COLOR      0x0f
#else
#define COLOR_ARRAY_SIZE 32768
#define BITS_PER_PRIM_COLOR 5
#define MAX_PRIM_COLOR      0x1f
#endif /* __MSDOS__ */

extern int _GifError;

#ifdef SYSV
static char *VersionStr =
        "Gif library module,\t\tGershon Elber\n\
      (C) Copyright 1989 Gershon Elber, Non commercial use only.\n";
#else
static char *VersionStr =
      PROGRAM_NAME
      "     IBMPC "
      GIF_LIB_VERSION
      "     Gershon Elber,    "
      __DATE__ ",   " __TIME__ "\n"
      "(C) Copyright 1989 Gershon Elber, Non commercial use only.\n";
#endif /* SYSV */

static int SortRGBAxis;

typedef struct QuantizedColorType {
    GifByteType RGB[3];
    GifByteType NewColorIndex;
    long Count;
    struct QuantizedColorType *Pnext;
} QuantizedColorType;

typedef struct NewColorMapType {
    GifByteType RGBMin[3], RGBWidth[3];
    unsigned int NumEntries;/* # of QuantizedColorType in linked list below. */
    long Count;                /* Total number of pixels in all the entries. */
    QuantizedColorType *QuantizedColors;
} NewColorMapType;

static int SubdivColorMap(NewColorMapType *NewColorSubdiv,
                    unsigned int ColorMapSize,
                    unsigned int *NewColorMapSize);
#ifdef __MSDOS__
static int SortCmpRtn(const VoidPtr Entry1, const VoidPtr Entry2);
#else
static int SortCmpRtn(VoidPtr Entry1, VoidPtr Entry2);
#endif /* __MSDOS__ */

/******************************************************************************
* Quantize high resolution image into lower one. Input image consists of a    *
* 2D array for each of the RGB colors with size Width by Height. There is no  *
* Color map for the input. Output is a quantized image with 2D array of       *
* indexes into the output color map.                                    *
*   Note input image can be 24 bits at the most (8 for red/green/blue) and    *
* the output has 256 colors at the most (256 entries in the color map.).      *
* ColorMapSize specifies size of color map up to 256 and will be updated to   *
* real size before returning.                                     *
*   Also non of the parameter are allocated by this routine.                  *
*   This function returns GIF_OK if succesfull, GIF_ERROR otherwise.          *
******************************************************************************/
int QuantizeBuffer(unsigned int Width, unsigned int Height, int *ColorMapSize,
      GifByteType *RedInput, GifByteType *GreenInput, GifByteType *BlueInput,
      GifByteType *OutputBuffer, GifColorType *OutputColorMap)
{
    unsigned int Index, NumOfEntries;
    int i, j, MaxRGBError[3];
    int NewColorMapSize;
    long Red, Green, Blue;
    NewColorMapType NewColorSubdiv[256];
    QuantizedColorType *ColorArrayEntries, *QuantizedColor;

    if ((ColorArrayEntries = (QuantizedColorType *)
          malloc(sizeof(QuantizedColorType) * COLOR_ARRAY_SIZE)) == NULL) {
      _GifError = E_GIF_ERR_NOT_ENOUGH_MEM;
      return GIF_ERROR;
    }

    for (i = 0; i < COLOR_ARRAY_SIZE; i++) {
      ColorArrayEntries[i].RGB[0]= i >> (2 * BITS_PER_PRIM_COLOR);
      ColorArrayEntries[i].RGB[1] = (i >> BITS_PER_PRIM_COLOR) &
                                          MAX_PRIM_COLOR;
      ColorArrayEntries[i].RGB[2] = i & MAX_PRIM_COLOR;
      ColorArrayEntries[i].Count = 0;
    }

    /* Sample the colors and their distribution: */
    for (i = 0; i < (int)(Width * Height); i++) {
      Index = ((RedInput[i] >> (8 - BITS_PER_PRIM_COLOR))
                << (2 * BITS_PER_PRIM_COLOR)) +
            ((GreenInput[i] >> (8 - BITS_PER_PRIM_COLOR))
                << BITS_PER_PRIM_COLOR) +
            (BlueInput[i] >> (8 - BITS_PER_PRIM_COLOR));
      ColorArrayEntries[Index].Count++;
    }

    /* Put all the colors in the first entry of the color map, and call the  */
    /* recursive subdivision process.                                  */
    for (i = 0; i < 256; i++) {
      NewColorSubdiv[i].QuantizedColors = NULL;
      NewColorSubdiv[i].Count = NewColorSubdiv[i].NumEntries = 0;
      for (j = 0; j < 3; j++) {
          NewColorSubdiv[i].RGBMin[j] = 0;
          NewColorSubdiv[i].RGBWidth[j] = 255;
      }
    }

    /* Find the non empty entries in the color table and chain them: */
    for (i = 0; i < COLOR_ARRAY_SIZE; i++)
      if (ColorArrayEntries[i].Count > 0) break;
    QuantizedColor = NewColorSubdiv[0].QuantizedColors = &ColorArrayEntries[i];
    NumOfEntries = 1;
    while (++i < COLOR_ARRAY_SIZE)
      if (ColorArrayEntries[i].Count > 0) {
          QuantizedColor -> Pnext = &ColorArrayEntries[i];
          QuantizedColor = &ColorArrayEntries[i];
          NumOfEntries++;
      }
    QuantizedColor -> Pnext = NULL;

    NewColorSubdiv[0].NumEntries = NumOfEntries;/* Different sampled colors. */
    NewColorSubdiv[0].Count = ((long) Width) * Height;            /* Pixels. */
    NewColorMapSize = 1;
    if (SubdivColorMap(NewColorSubdiv, *ColorMapSize, &NewColorMapSize) !=
                                                     GIF_OK) {
      free((char *) ColorArrayEntries);
      return GIF_ERROR;
    }
    if (NewColorMapSize < *ColorMapSize) {
      /* And clear rest of color map: */
      for (i = NewColorMapSize; i < *ColorMapSize; i++)
          OutputColorMap[i].Red =
          OutputColorMap[i].Green =
          OutputColorMap[i].Blue = 0;
    }

    /* Average the colors in each entry to be the color to be used in the    */
    /* output color map, and plug it into the output color map itself.       */
    for (i = 0; i < NewColorMapSize; i++) {
      if ((j = NewColorSubdiv[i].NumEntries) > 0) {
          QuantizedColor = NewColorSubdiv[i].QuantizedColors;
          Red = Green = Blue = 0;
          while (QuantizedColor) {
            QuantizedColor -> NewColorIndex = i;
            Red += QuantizedColor -> RGB[0];
            Green += QuantizedColor -> RGB[1];
            Blue += QuantizedColor -> RGB[2];
            QuantizedColor = QuantizedColor -> Pnext;
          }
          OutputColorMap[i].Red = (Red << (8 - BITS_PER_PRIM_COLOR)) / j;
          OutputColorMap[i].Green = (Green << (8 - BITS_PER_PRIM_COLOR)) / j;
          OutputColorMap[i].Blue= (Blue << (8 - BITS_PER_PRIM_COLOR)) / j;
      }
      else
          GIF_MESSAGE("Null entry in quantized color map - thats weird.");
    }

    /* Finally scan the input buffer again and put the mapped index in the   */
    /* output buffer.                                            */
    MaxRGBError[0] = MaxRGBError[1] = MaxRGBError[2] = 0;
    for (i = 0; i < (int)(Width * Height); i++) {
      Index = ((RedInput[i] >> (8 - BITS_PER_PRIM_COLOR))
                << (2 * BITS_PER_PRIM_COLOR)) +
            ((GreenInput[i] >> (8 - BITS_PER_PRIM_COLOR))
                << BITS_PER_PRIM_COLOR) +
            (BlueInput[i] >> (8 - BITS_PER_PRIM_COLOR));
      Index = ColorArrayEntries[Index].NewColorIndex;
      OutputBuffer[i] = Index;
      if (MaxRGBError[0] < ABS(OutputColorMap[Index].Red - RedInput[i]))
          MaxRGBError[0] = ABS(OutputColorMap[Index].Red - RedInput[i]);
      if (MaxRGBError[1] < ABS(OutputColorMap[Index].Green - GreenInput[i]))
          MaxRGBError[1] = ABS(OutputColorMap[Index].Green - GreenInput[i]);
      if (MaxRGBError[2] < ABS(OutputColorMap[Index].Blue - BlueInput[i]))
          MaxRGBError[2] = ABS(OutputColorMap[Index].Blue - BlueInput[i]);
    }

#ifdef DEBUG
    fprintf(stderr,
          "Quantization L(0) errors: Red = %d, Green = %d, Blue = %d.\n",
                      MaxRGBError[0], MaxRGBError[1], MaxRGBError[2]);
#endif /* DEBUG */

    free((char *) ColorArrayEntries);

    *ColorMapSize = NewColorMapSize;

    return GIF_OK;
}

/******************************************************************************
* Routine to subdivide the RGB space recursively using median cut in each     *
* axes alternatingly until ColorMapSize different cubes exists.               *
* The biggest cube in one dimension is subdivide unless it has only one entry.*
* Returns GIF_ERROR if failed, otherwise GIF_OK.                        *
******************************************************************************/
static int SubdivColorMap(NewColorMapType *NewColorSubdiv,
                    unsigned int ColorMapSize,
                    unsigned int *NewColorMapSize)
{
    int MaxSize;
    unsigned int i, j, Index = 0, NumEntries, MinColor, MaxColor;
    long Sum, Count;
    QuantizedColorType *QuantizedColor, **SortArray;

    while (ColorMapSize > *NewColorMapSize) {
      /* Find candidate for subdivision: */
      MaxSize = -1;
      for (i = 0; i < *NewColorMapSize; i++) {
          for (j = 0; j < 3; j++) {
            if (((int) NewColorSubdiv[i].RGBWidth[j]) > MaxSize &&
                NewColorSubdiv[i].NumEntries > 1) {
                MaxSize = NewColorSubdiv[i].RGBWidth[j];
                Index = i;
                SortRGBAxis = j;
            }
          }
      }

      if (MaxSize == -1)
          return GIF_OK;

      /* Split the entry Index into two along the axis SortRGBAxis: */

      /* Sort all elements in that entry along the given axis and split at */
      /* the median.                                             */
      if ((SortArray = (QuantizedColorType **)
          malloc(sizeof(QuantizedColorType *) *
               NewColorSubdiv[Index].NumEntries)) == NULL)
          return GIF_ERROR;
      for (j = 0, QuantizedColor = NewColorSubdiv[Index].QuantizedColors;
           j < NewColorSubdiv[Index].NumEntries && QuantizedColor != NULL;
           j++, QuantizedColor = QuantizedColor -> Pnext)
          SortArray[j] = QuantizedColor;
      qsort(SortArray, NewColorSubdiv[Index].NumEntries,
            sizeof(QuantizedColorType *), SortCmpRtn);

      /* Relink the sorted list into one: */
      for (j = 0; j < NewColorSubdiv[Index].NumEntries - 1; j++)
          SortArray[j] -> Pnext = SortArray[j + 1];
      SortArray[NewColorSubdiv[Index].NumEntries - 1] -> Pnext = NULL;
      NewColorSubdiv[Index].QuantizedColors = QuantizedColor = SortArray[0];
      free((char *) SortArray);

      /* Now simply add the Counts until we have half of the Count: */
      Sum = NewColorSubdiv[Index].Count / 2 - QuantizedColor -> Count;
      NumEntries = 1;
      Count = QuantizedColor -> Count;
      while ((Sum -= QuantizedColor -> Pnext -> Count) >= 0 &&
             QuantizedColor -> Pnext != NULL &&
             QuantizedColor -> Pnext -> Pnext != NULL) {
          QuantizedColor = QuantizedColor -> Pnext;
          NumEntries++;
          Count += QuantizedColor -> Count;
      }
      /* Save the values of the last color of the first half, and first    */
      /* of the second half so we can update the Bounding Boxes later.     */
      /* Also as the colors are quantized and the BBoxes are full 0..255,  */
      /* they need to be rescaled.                               */
      MaxColor = QuantizedColor -> RGB[SortRGBAxis];/* Max. of first half. */
      MinColor = QuantizedColor -> Pnext -> RGB[SortRGBAxis];/* of second. */
      MaxColor <<= (8 - BITS_PER_PRIM_COLOR);
      MinColor <<= (8 - BITS_PER_PRIM_COLOR);

      /* Partition right here: */
      NewColorSubdiv[*NewColorMapSize].QuantizedColors =
          QuantizedColor -> Pnext;
      QuantizedColor -> Pnext = NULL;
      NewColorSubdiv[*NewColorMapSize].Count = Count;
      NewColorSubdiv[Index].Count -= Count;
      NewColorSubdiv[*NewColorMapSize].NumEntries =
          NewColorSubdiv[Index].NumEntries - NumEntries;
      NewColorSubdiv[Index].NumEntries = NumEntries;
      for (j = 0; j < 3; j++) {
          NewColorSubdiv[*NewColorMapSize].RGBMin[j] =
            NewColorSubdiv[Index].RGBMin[j];
          NewColorSubdiv[*NewColorMapSize].RGBWidth[j] =
            NewColorSubdiv[Index].RGBWidth[j];
      }
      NewColorSubdiv[*NewColorMapSize].RGBWidth[SortRGBAxis] =
          NewColorSubdiv[*NewColorMapSize].RGBMin[SortRGBAxis] +
          NewColorSubdiv[*NewColorMapSize].RGBWidth[SortRGBAxis] -
          MinColor;
      NewColorSubdiv[*NewColorMapSize].RGBMin[SortRGBAxis] = MinColor;

      NewColorSubdiv[Index].RGBWidth[SortRGBAxis] =
          MaxColor - NewColorSubdiv[Index].RGBMin[SortRGBAxis];

      (*NewColorMapSize)++;
    }

    return GIF_OK;
}

/******************************************************************************
* Routine called by qsort to compare to entries.                        *
******************************************************************************/
#ifdef __MSDOS__
static int SortCmpRtn(const VoidPtr Entry1, const VoidPtr Entry2)
#else
static int SortCmpRtn(VoidPtr Entry1, VoidPtr Entry2)
#endif /* __MSDOS__ */
{
    return (* ((QuantizedColorType **) Entry1)) -> RGB[SortRGBAxis] -
         (* ((QuantizedColorType **) Entry2)) -> RGB[SortRGBAxis];
}

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