gifquantize.c

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/* @(#)root/x11:$Id$ */
/* Author: Fons Rademakers   04/11/98*/
/*****************************************************************************
* Module to quantize 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.                                                *
*****************************************************************************/

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

typedef unsigned char byte;
typedef struct GifColorType {
    byte Red, Green, Blue;
} GifColorType;

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

#define GIF_ERROR     0
#define GIF_OK        1

/* The colors are stripped to 5 bits per primary color */
#define COLOR_ARRAY_SIZE 32768
#define BITS_PER_PRIM_COLOR 5
#define MAX_PRIM_COLOR      0x1f


static int SortRGBAxis;

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

typedef struct NewColorMapType {
   byte 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);
static int SortCmpRtn(const void *Entry1, const void *Entry2);


/******************************************************************************
* 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 successful, GIF_ERROR otherwise.          *
******************************************************************************/
int GIFquantize(unsigned int Width, unsigned int Height, int *ColorMapSize,
        byte *RedInput, byte *GreenInput, byte *BlueInput,
        byte *OutputBuffer, GifColorType *OutputColorMap)
{
    unsigned int Index, NumOfEntries, newsize;
    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) {
        fprintf(stderr, "QuantizeBuffer: not enough memory\n");
        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. */
    newsize = 1;
    if (SubdivColorMap(NewColorSubdiv, *ColorMapSize, &newsize) != GIF_OK) {
        free((char *) ColorArrayEntries);
        return GIF_ERROR;
    }
    NewColorMapSize = (int)newsize;
    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
            fprintf(stderr, "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 (QuantizedColor -> Pnext != NULL &&
               QuantizedColor -> Pnext -> Pnext != NULL &&
               (Sum -= QuantizedColor -> Pnext -> Count) >= 0) {
            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. */
        if (QuantizedColor -> Pnext) MinColor = QuantizedColor -> Pnext -> RGB[SortRGBAxis];/* of second. */
        else MinColor = 0;
        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.                              *
******************************************************************************/
static int SortCmpRtn(const void *Entry1, const void *Entry2)
{
    return (* ((QuantizedColorType **) Entry1)) -> RGB[SortRGBAxis] -
           (* ((QuantizedColorType **) Entry2)) -> RGB[SortRGBAxis];
}