www.pudn.com > imgport.rar > jquant1.c, change:2008-11-05,size:32185b


/* 
 * jquant1.c 
 * 
 * Copyright (C) 1991-1996, Thomas G. Lane. 
 * This file is part of the Independent JPEG Group's software. 
 * For conditions of distribution and use, see the accompanying README file. 
 * 
 * This file contains 1-pass color quantization (color mapping) routines. 
 * These routines provide mapping to a fixed color map using equally spaced 
 * color values.  Optional Floyd-Steinberg or ordered dithering is available. 
 */ 
 
#define JPEG_INTERNALS 
#include "jinclude.h" 
#include "jpeglib.h" 
 
#ifdef QUANT_1PASS_SUPPORTED 
 
 
/* 
 * The main purpose of 1-pass quantization is to provide a fast, if not very 
 * high quality, colormapped output capability.  A 2-pass quantizer usually 
 * gives better visual quality; however, for quantized grayscale output this 
 * quantizer is perfectly adequate.  Dithering is highly recommended with this 
 * quantizer, though you can turn it off if you really want to. 
 * 
 * In 1-pass quantization the colormap must be chosen in advance of seeing the 
 * image.  We use a map consisting of all combinations of Ncolors[i] color 
 * values for the i'th component.  The Ncolors[] values are chosen so that 
 * their product, the total number of colors, is no more than that requested. 
 * (In most cases, the product will be somewhat less.) 
 * 
 * Since the colormap is orthogonal, the representative value for each color 
 * component can be determined without considering the other components; 
 * then these indexes can be combined into a colormap index by a standard 
 * N-dimensional-array-subscript calculation.  Most of the arithmetic involved 
 * can be precalculated and stored in the lookup table colorindex[]. 
 * colorindex[i][j] maps pixel value j in component i to the nearest 
 * representative value (grid plane) for that component; this index is 
 * multiplied by the array stride for component i, so that the 
 * index of the colormap entry closest to a given pixel value is just 
 *    sum( colorindex[component-number][pixel-component-value] ) 
 * Aside from being fast, this scheme allows for variable spacing between 
 * representative values with no additional lookup cost. 
 * 
 * If gamma correction has been applied in color conversion, it might be wise 
 * to adjust the color grid spacing so that the representative colors are 
 * equidistant in linear space.  At this writing, gamma correction is not 
 * implemented by jdcolor, so nothing is done here. 
 */ 
 
 
/* Declarations for ordered dithering. 
 * 
 * We use a standard 16x16 ordered dither array.  The basic concept of ordered 
 * dithering is described in many references, for instance Dale Schumacher's 
 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991). 
 * In place of Schumacher's comparisons against a "threshold" value, we add a 
 * "dither" value to the input pixel and then round the result to the nearest 
 * output value.  The dither value is equivalent to (0.5 - threshold) times 
 * the distance between output values.  For ordered dithering, we assume that 
 * the output colors are equally spaced; if not, results will probably be 
 * worse, since the dither may be too much or too little at a given point. 
 * 
 * The normal calculation would be to form pixel value + dither, range-limit 
 * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual. 
 * We can skip the separate range-limiting step by extending the colorindex 
 * table in both directions. 
 */ 
 
#define ODITHER_SIZE  16	/* dimension of dither matrix */ 
/* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */ 
#define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE)	/* # cells in matrix */ 
#define ODITHER_MASK  (ODITHER_SIZE-1) /* mask for wrapping around counters */ 
 
typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE]; 
typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE]; 
 
static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = { 
  /* Bayer's order-4 dither array.  Generated by the code given in 
   * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I. 
   * The values in this array must range from 0 to ODITHER_CELLS-1. 
   */ 
  {   0,192, 48,240, 12,204, 60,252,  3,195, 51,243, 15,207, 63,255 }, 
  { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 }, 
  {  32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 }, 
  { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 }, 
  {   8,200, 56,248,  4,196, 52,244, 11,203, 59,251,  7,199, 55,247 }, 
  { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 }, 
  {  40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 }, 
  { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 }, 
  {   2,194, 50,242, 14,206, 62,254,  1,193, 49,241, 13,205, 61,253 }, 
  { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 }, 
  {  34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 }, 
  { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 }, 
  {  10,202, 58,250,  6,198, 54,246,  9,201, 57,249,  5,197, 53,245 }, 
  { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 }, 
  {  42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 }, 
  { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 } 
}; 
 
 
/* Declarations for Floyd-Steinberg dithering. 
 * 
 * Errors are accumulated into the array fserrors[], at a resolution of 
 * 1/16th of a pixel count.  The error at a given pixel is propagated 
 * to its not-yet-processed neighbors using the standard F-S fractions, 
 *		...	(here)	7/16 
 *		3/16	5/16	1/16 
 * We work left-to-right on even rows, right-to-left on odd rows. 
 * 
 * We can get away with a single array (holding one row's worth of errors) 
 * by using it to store the current row's errors at pixel columns not yet 
 * processed, but the next row's errors at columns already processed.  We 
 * need only a few extra variables to hold the errors immediately around the 
 * current column.  (If we are lucky, those variables are in registers, but 
 * even if not, they're probably cheaper to access than array elements are.) 
 * 
 * The fserrors[] array is indexed [component#][position]. 
 * We provide (#columns + 2) entries per component; the extra entry at each 
 * end saves us from special-casing the first and last pixels. 
 * 
 * Note: on a wide image, we might not have enough room in a PC's near data 
 * segment to hold the error array; so it is allocated with alloc_large. 
 */ 
 
#if BITS_IN_JSAMPLE == 8 
typedef INT16 FSERROR;		/* 16 bits should be enough */ 
typedef int LOCFSERROR;		/* use 'int' for calculation temps */ 
#else 
typedef JPEG_INT32 FSERROR;		/* may need more than 16 bits */ 
typedef JPEG_INT32 LOCFSERROR;	/* be sure calculation temps are big enough */ 
#endif 
 
typedef FSERROR FAR *FSERRPTR;	/* pointer to error array (in FAR storage!) */ 
 
 
/* Private subobject */ 
 
#define MAX_Q_COMPS 4		/* max components I can handle */ 
 
typedef struct { 
  struct jpeg_color_quantizer pub; /* public fields */ 
 
  /* Initially allocated colormap is saved here */ 
  JSAMPARRAY sv_colormap;	/* The color map as a 2-D pixel array */ 
  int sv_actual;		/* number of entries in use */ 
 
  JSAMPARRAY colorindex;	/* Precomputed mapping for speed */ 
  /* colorindex[i][j] = index of color closest to pixel value j in component i, 
   * premultiplied as described above.  Since colormap indexes must fit into 
   * JSAMPLEs, the entries of this array will too. 
   */ 
  boolean is_padded;		/* is the colorindex padded for odither? */ 
 
  int Ncolors[MAX_Q_COMPS];	/* # of values alloced to each component */ 
 
  /* Variables for ordered dithering */ 
  int row_index;		/* cur row's vertical index in dither matrix */ 
  ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */ 
 
  /* Variables for Floyd-Steinberg dithering */ 
  FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */ 
  boolean on_odd_row;		/* flag to remember which row we are on */ 
} my_cquantizer; 
 
typedef my_cquantizer * my_cquantize_ptr; 
 
 
/* 
 * Policy-making subroutines for create_colormap and create_colorindex. 
 * These routines determine the colormap to be used.  The rest of the module 
 * only assumes that the colormap is orthogonal. 
 * 
 *  * select_ncolors decides how to divvy up the available colors 
 *    among the components. 
 *  * output_value defines the set of representative values for a component. 
 *  * largest_input_value defines the mapping from input values to 
 *    representative values for a component. 
 * Note that the latter two routines may impose different policies for 
 * different components, though this is not currently done. 
 */ 
 
 
LOCAL(int) 
select_ncolors (j_decompress_ptr cinfo, int Ncolors[]) 
/* Determine allocation of desired colors to components, */ 
/* and fill in Ncolors[] array to indicate choice. */ 
/* Return value is total number of colors (product of Ncolors[] values). */ 
{ 
  int nc = cinfo->out_color_components; /* number of color components */ 
  int max_colors = cinfo->desired_number_of_colors; 
  int total_colors, iroot, i, j; 
  boolean changed; 
  long temp; 
  static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE }; 
 
  /* We can allocate at least the nc'th root of max_colors per component. */ 
  /* Compute floor(nc'th root of max_colors). */ 
  iroot = 1; 
  do { 
    iroot++; 
    temp = iroot;		/* set temp = iroot ** nc */ 
    for (i = 1; i < nc; i++) 
      temp *= iroot; 
  } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */ 
  iroot--;			/* now iroot = floor(root) */ 
 
  /* Must have at least 2 color values per component */ 
  if (iroot < 2) 
    ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp); 
 
  /* Initialize to iroot color values for each component */ 
  total_colors = 1; 
  for (i = 0; i < nc; i++) { 
    Ncolors[i] = iroot; 
    total_colors *= iroot; 
  } 
  /* We may be able to increment the count for one or more components without 
   * exceeding max_colors, though we know not all can be incremented. 
   * Sometimes, the first component can be incremented more than once! 
   * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.) 
   * In RGB colorspace, try to increment G first, then R, then B. 
   */ 
  do { 
    changed = FALSE; 
    for (i = 0; i < nc; i++) { 
      j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i); 
      /* calculate new total_colors if Ncolors[j] is incremented */ 
      temp = total_colors / Ncolors[j]; 
      temp *= Ncolors[j]+1;	/* done in long arith to avoid oflo */ 
      if (temp > (long) max_colors) 
	break;			/* won't fit, done with this pass */ 
      Ncolors[j]++;		/* OK, apply the increment */ 
      total_colors = (int) temp; 
      changed = TRUE; 
    } 
  } while (changed); 
 
  return total_colors; 
} 
 
 
LOCAL(int) 
output_value (j_decompress_ptr cinfo, int ci, int j, int maxj) 
/* Return j'th output value, where j will range from 0 to maxj */ 
/* The output values must fall in 0..MAXJSAMPLE in increasing order */ 
{ 
  /* We always provide values 0 and MAXJSAMPLE for each component; 
   * any additional values are equally spaced between these limits. 
   * (Forcing the upper and lower values to the limits ensures that 
   * dithering can't produce a color outside the selected gamut.) 
   */ 
  return (int) (((JPEG_INT32) j * MAXJSAMPLE + maxj/2) / maxj); 
} 
 
 
LOCAL(int) 
largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj) 
/* Return largest input value that should map to j'th output value */ 
/* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */ 
{ 
  /* Breakpoints are halfway between values returned by output_value */ 
  return (int) (((JPEG_INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj)); 
} 
 
 
/* 
 * Create the colormap. 
 */ 
 
LOCAL(void) 
create_colormap (j_decompress_ptr cinfo) 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  JSAMPARRAY colormap;		/* Created colormap */ 
  int total_colors;		/* Number of distinct output colors */ 
  int i,j,k, nci, blksize, blkdist, ptr, val; 
 
  /* Select number of colors for each component */ 
  total_colors = select_ncolors(cinfo, cquantize->Ncolors); 
 
  /* Report selected color counts */ 
  if (cinfo->out_color_components == 3) 
    TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS, 
	     total_colors, cquantize->Ncolors[0], 
	     cquantize->Ncolors[1], cquantize->Ncolors[2]); 
  else 
    TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors); 
 
  /* Allocate and fill in the colormap. */ 
  /* The colors are ordered in the map in standard row-major order, */ 
  /* i.e. rightmost (highest-indexed) color changes most rapidly. */ 
 
  colormap = (*cinfo->mem->alloc_sarray) 
    ((j_common_ptr) cinfo, JPOOL_IMAGE, 
     (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components); 
 
  /* blksize is number of adjacent repeated entries for a component */ 
  /* blkdist is distance between groups of identical entries for a component */ 
  blkdist = total_colors; 
 
  for (i = 0; i < cinfo->out_color_components; i++) { 
    /* fill in colormap entries for i'th color component */ 
    nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 
    blksize = blkdist / nci; 
    for (j = 0; j < nci; j++) { 
      /* Compute j'th output value (out of nci) for component */ 
      val = output_value(cinfo, i, j, nci-1); 
      /* Fill in all colormap entries that have this value of this component */ 
      for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) { 
	/* fill in blksize entries beginning at ptr */ 
	for (k = 0; k < blksize; k++) 
	  colormap[i][ptr+k] = (JSAMPLE) val; 
      } 
    } 
    blkdist = blksize;		/* blksize of this color is blkdist of next */ 
  } 
 
  /* Save the colormap in private storage, 
   * where it will survive color quantization mode changes. 
   */ 
  cquantize->sv_colormap = colormap; 
  cquantize->sv_actual = total_colors; 
} 
 
 
/* 
 * Create the color index table. 
 */ 
 
LOCAL(void) 
create_colorindex (j_decompress_ptr cinfo) 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  JSAMPROW indexptr; 
  int i,j,k, nci, blksize, val, pad; 
 
  /* For ordered dither, we pad the color index tables by MAXJSAMPLE in 
   * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE). 
   * This is not necessary in the other dithering modes.  However, we 
   * flag whether it was done in case user changes dithering mode. 
   */ 
  if (cinfo->dither_mode == JDITHER_ORDERED) { 
    pad = MAXJSAMPLE*2; 
    cquantize->is_padded = TRUE; 
  } else { 
    pad = 0; 
    cquantize->is_padded = FALSE; 
  } 
 
  cquantize->colorindex = (*cinfo->mem->alloc_sarray) 
    ((j_common_ptr) cinfo, JPOOL_IMAGE, 
     (JDIMENSION) (MAXJSAMPLE+1 + pad), 
     (JDIMENSION) cinfo->out_color_components); 
 
  /* blksize is number of adjacent repeated entries for a component */ 
  blksize = cquantize->sv_actual; 
 
  for (i = 0; i < cinfo->out_color_components; i++) { 
    /* fill in colorindex entries for i'th color component */ 
    nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 
    blksize = blksize / nci; 
 
    /* adjust colorindex pointers to provide padding at negative indexes. */ 
    if (pad) 
      cquantize->colorindex[i] += MAXJSAMPLE; 
 
    /* in loop, val = index of current output value, */ 
    /* and k = largest j that maps to current val */ 
    indexptr = cquantize->colorindex[i]; 
    val = 0; 
    k = largest_input_value(cinfo, i, 0, nci-1); 
    for (j = 0; j <= MAXJSAMPLE; j++) { 
      while (j > k)		/* advance val if past boundary */ 
	k = largest_input_value(cinfo, i, ++val, nci-1); 
      /* premultiply so that no multiplication needed in main processing */ 
      indexptr[j] = (JSAMPLE) (val * blksize); 
    } 
    /* Pad at both ends if necessary */ 
    if (pad) 
      for (j = 1; j <= MAXJSAMPLE; j++) { 
	indexptr[-j] = indexptr[0]; 
	indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE]; 
      } 
  } 
} 
 
 
/* 
 * Create an ordered-dither array for a component having ncolors 
 * distinct output values. 
 */ 
 
LOCAL(ODITHER_MATRIX_PTR) 
make_odither_array (j_decompress_ptr cinfo, int ncolors) 
{ 
  ODITHER_MATRIX_PTR odither; 
  int j,k; 
  JPEG_INT32 num,den; 
 
  odither = (ODITHER_MATRIX_PTR) 
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				SIZEOF(ODITHER_MATRIX)); 
  /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1). 
   * Hence the dither value for the matrix cell with fill order f 
   * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1). 
   * On 16-bit-int machine, be careful to avoid overflow. 
   */ 
  den = 2 * ODITHER_CELLS * ((JPEG_INT32) (ncolors - 1)); 
  for (j = 0; j < ODITHER_SIZE; j++) { 
    for (k = 0; k < ODITHER_SIZE; k++) { 
      num = ((JPEG_INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k]))) 
	    * MAXJSAMPLE; 
      /* Ensure round towards zero despite C's lack of consistency 
       * about rounding negative values in integer division... 
       */ 
      odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den); 
    } 
  } 
  return odither; 
} 
 
 
/* 
 * Create the ordered-dither tables. 
 * Components having the same number of representative colors may  
 * share a dither table. 
 */ 
 
LOCAL(void) 
create_odither_tables (j_decompress_ptr cinfo) 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  ODITHER_MATRIX_PTR odither; 
  int i, j, nci; 
 
  for (i = 0; i < cinfo->out_color_components; i++) { 
    nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 
    odither = NULL;		/* search for matching prior component */ 
    for (j = 0; j < i; j++) { 
      if (nci == cquantize->Ncolors[j]) { 
	odither = cquantize->odither[j]; 
	break; 
      } 
    } 
    if (odither == NULL)	/* need a new table? */ 
      odither = make_odither_array(cinfo, nci); 
    cquantize->odither[i] = odither; 
  } 
} 
 
 
/* 
 * Map some rows of pixels to the output colormapped representation. 
 */ 
 
METHODDEF(void) 
color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 
		JSAMPARRAY output_buf, int num_rows) 
/* General case, no dithering */ 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  JSAMPARRAY colorindex = cquantize->colorindex; 
  register int pixcode, ci; 
  register JSAMPROW ptrin, ptrout; 
  int row; 
  JDIMENSION col; 
  JDIMENSION width = cinfo->output_width; 
  register int nc = cinfo->out_color_components; 
 
  for (row = 0; row < num_rows; row++) { 
    ptrin = input_buf[row]; 
    ptrout = output_buf[row]; 
    for (col = width; col > 0; col--) { 
      pixcode = 0; 
      for (ci = 0; ci < nc; ci++) { 
	pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]); 
      } 
      *ptrout++ = (JSAMPLE) pixcode; 
    } 
  } 
} 
 
 
METHODDEF(void) 
color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 
		 JSAMPARRAY output_buf, int num_rows) 
/* Fast path for out_color_components==3, no dithering */ 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  register int pixcode; 
  register JSAMPROW ptrin, ptrout; 
  JSAMPROW colorindex0 = cquantize->colorindex[0]; 
  JSAMPROW colorindex1 = cquantize->colorindex[1]; 
  JSAMPROW colorindex2 = cquantize->colorindex[2]; 
  int row; 
  JDIMENSION col; 
  JDIMENSION width = cinfo->output_width; 
 
  for (row = 0; row < num_rows; row++) { 
    ptrin = input_buf[row]; 
    ptrout = output_buf[row]; 
    for (col = width; col > 0; col--) { 
      pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]); 
      pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]); 
      pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]); 
      *ptrout++ = (JSAMPLE) pixcode; 
    } 
  } 
} 
 
 
METHODDEF(void) 
quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 
		     JSAMPARRAY output_buf, int num_rows) 
/* General case, with ordered dithering */ 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  register JSAMPROW input_ptr; 
  register JSAMPROW output_ptr; 
  JSAMPROW colorindex_ci; 
  int * dither;			/* points to active row of dither matrix */ 
  int row_index, col_index;	/* current indexes into dither matrix */ 
  int nc = cinfo->out_color_components; 
  int ci; 
  int row; 
  JDIMENSION col; 
  JDIMENSION width = cinfo->output_width; 
 
  for (row = 0; row < num_rows; row++) { 
    /* Initialize output values to 0 so can process components separately */ 
    jzero_far((void FAR *) output_buf[row], 
	      (size_t) (width * SIZEOF(JSAMPLE))); 
    row_index = cquantize->row_index; 
    for (ci = 0; ci < nc; ci++) { 
      input_ptr = input_buf[row] + ci; 
      output_ptr = output_buf[row]; 
      colorindex_ci = cquantize->colorindex[ci]; 
      dither = cquantize->odither[ci][row_index]; 
      col_index = 0; 
 
      for (col = width; col > 0; col--) { 
	/* Form pixel value + dither, range-limit to 0..MAXJSAMPLE, 
	 * select output value, accumulate into output code for this pixel. 
	 * Range-limiting need not be done explicitly, as we have extended 
	 * the colorindex table to produce the right answers for out-of-range 
	 * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the 
	 * required amount of padding. 
	 */ 
	*output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]]; 
	input_ptr += nc; 
	output_ptr++; 
	col_index = (col_index + 1) & ODITHER_MASK; 
      } 
    } 
    /* Advance row index for next row */ 
    row_index = (row_index + 1) & ODITHER_MASK; 
    cquantize->row_index = row_index; 
  } 
} 
 
 
METHODDEF(void) 
quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 
		      JSAMPARRAY output_buf, int num_rows) 
/* Fast path for out_color_components==3, with ordered dithering */ 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  register int pixcode; 
  register JSAMPROW input_ptr; 
  register JSAMPROW output_ptr; 
  JSAMPROW colorindex0 = cquantize->colorindex[0]; 
  JSAMPROW colorindex1 = cquantize->colorindex[1]; 
  JSAMPROW colorindex2 = cquantize->colorindex[2]; 
  int * dither0;		/* points to active row of dither matrix */ 
  int * dither1; 
  int * dither2; 
  int row_index, col_index;	/* current indexes into dither matrix */ 
  int row; 
  JDIMENSION col; 
  JDIMENSION width = cinfo->output_width; 
 
  for (row = 0; row < num_rows; row++) { 
    row_index = cquantize->row_index; 
    input_ptr = input_buf[row]; 
    output_ptr = output_buf[row]; 
    dither0 = cquantize->odither[0][row_index]; 
    dither1 = cquantize->odither[1][row_index]; 
    dither2 = cquantize->odither[2][row_index]; 
    col_index = 0; 
 
    for (col = width; col > 0; col--) { 
      pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) + 
					dither0[col_index]]); 
      pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) + 
					dither1[col_index]]); 
      pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) + 
					dither2[col_index]]); 
      *output_ptr++ = (JSAMPLE) pixcode; 
      col_index = (col_index + 1) & ODITHER_MASK; 
    } 
    row_index = (row_index + 1) & ODITHER_MASK; 
    cquantize->row_index = row_index; 
  } 
} 
 
 
METHODDEF(void) 
quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 
		    JSAMPARRAY output_buf, int num_rows) 
/* General case, with Floyd-Steinberg dithering */ 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  register LOCFSERROR cur;	/* current error or pixel value */ 
  LOCFSERROR belowerr;		/* error for pixel below cur */ 
  LOCFSERROR bpreverr;		/* error for below/prev col */ 
  LOCFSERROR bnexterr;		/* error for below/next col */ 
  LOCFSERROR delta; 
  register FSERRPTR errorptr;	/* => fserrors[] at column before current */ 
  register JSAMPROW input_ptr; 
  register JSAMPROW output_ptr; 
  JSAMPROW colorindex_ci; 
  JSAMPROW colormap_ci; 
  int pixcode; 
  int nc = cinfo->out_color_components; 
  int dir;			/* 1 for left-to-right, -1 for right-to-left */ 
  int dirnc;			/* dir * nc */ 
  int ci; 
  int row; 
  JDIMENSION col; 
  JDIMENSION width = cinfo->output_width; 
  JSAMPLE *range_limit = cinfo->sample_range_limit; 
  SHIFT_TEMPS 
 
  for (row = 0; row < num_rows; row++) { 
    /* Initialize output values to 0 so can process components separately */ 
    jzero_far((void FAR *) output_buf[row], 
	      (size_t) (width * SIZEOF(JSAMPLE))); 
    for (ci = 0; ci < nc; ci++) { 
      input_ptr = input_buf[row] + ci; 
      output_ptr = output_buf[row]; 
      if (cquantize->on_odd_row) { 
	/* work right to left in this row */ 
	input_ptr += (width-1) * nc; /* so point to rightmost pixel */ 
	output_ptr += width-1; 
	dir = -1; 
	dirnc = -nc; 
	errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */ 
      } else { 
	/* work left to right in this row */ 
	dir = 1; 
	dirnc = nc; 
	errorptr = cquantize->fserrors[ci]; /* => entry before first column */ 
      } 
      colorindex_ci = cquantize->colorindex[ci]; 
      colormap_ci = cquantize->sv_colormap[ci]; 
      /* Preset error values: no error propagated to first pixel from left */ 
      cur = 0; 
      /* and no error propagated to row below yet */ 
      belowerr = bpreverr = 0; 
 
      for (col = width; col > 0; col--) { 
	/* cur holds the error propagated from the previous pixel on the 
	 * current line.  Add the error propagated from the previous line 
	 * to form the complete error correction term for this pixel, and 
	 * round the error term (which is expressed * 16) to an integer. 
	 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct 
	 * for either sign of the error value. 
	 * Note: errorptr points to *previous* column's array entry. 
	 */ 
	cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4); 
	/* Form pixel value + error, and range-limit to 0..MAXJSAMPLE. 
	 * The maximum error is +- MAXJSAMPLE; this sets the required size 
	 * of the range_limit array. 
	 */ 
	cur += GETJSAMPLE(*input_ptr); 
	cur = GETJSAMPLE(range_limit[cur]); 
	/* Select output value, accumulate into output code for this pixel */ 
	pixcode = GETJSAMPLE(colorindex_ci[cur]); 
	*output_ptr += (JSAMPLE) pixcode; 
	/* Compute actual representation error at this pixel */ 
	/* Note: we can do this even though we don't have the final */ 
	/* pixel code, because the colormap is orthogonal. */ 
	cur -= GETJSAMPLE(colormap_ci[pixcode]); 
	/* Compute error fractions to be propagated to adjacent pixels. 
	 * Add these into the running sums, and simultaneously shift the 
	 * next-line error sums left by 1 column. 
	 */ 
	bnexterr = cur; 
	delta = cur * 2; 
	cur += delta;		/* form error * 3 */ 
	errorptr[0] = (FSERROR) (bpreverr + cur); 
	cur += delta;		/* form error * 5 */ 
	bpreverr = belowerr + cur; 
	belowerr = bnexterr; 
	cur += delta;		/* form error * 7 */ 
	/* At this point cur contains the 7/16 error value to be propagated 
	 * to the next pixel on the current line, and all the errors for the 
	 * next line have been shifted over. We are therefore ready to move on. 
	 */ 
	input_ptr += dirnc;	/* advance input ptr to next column */ 
	output_ptr += dir;	/* advance output ptr to next column */ 
	errorptr += dir;	/* advance errorptr to current column */ 
      } 
      /* Post-loop cleanup: we must unload the final error value into the 
       * final fserrors[] entry.  Note we need not unload belowerr because 
       * it is for the dummy column before or after the actual array. 
       */ 
      errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */ 
    } 
    cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE); 
  } 
} 
 
 
/* 
 * Allocate workspace for Floyd-Steinberg errors. 
 */ 
 
LOCAL(void) 
alloc_fs_workspace (j_decompress_ptr cinfo) 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  size_t arraysize; 
  int i; 
 
  arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR)); 
  for (i = 0; i < cinfo->out_color_components; i++) { 
    cquantize->fserrors[i] = (FSERRPTR) 
      (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize); 
  } 
} 
 
 
/* 
 * Initialize for one-pass color quantization. 
 */ 
 
METHODDEF(void) 
start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan) 
{ 
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 
  size_t arraysize; 
  int i; 
 
  /* Install my colormap. */ 
  cinfo->colormap = cquantize->sv_colormap; 
  cinfo->actual_number_of_colors = cquantize->sv_actual; 
 
  /* Initialize for desired dithering mode. */ 
  switch (cinfo->dither_mode) { 
  case JDITHER_NONE: 
    if (cinfo->out_color_components == 3) 
      cquantize->pub.color_quantize = color_quantize3; 
    else 
      cquantize->pub.color_quantize = color_quantize; 
    break; 
  case JDITHER_ORDERED: 
    if (cinfo->out_color_components == 3) 
      cquantize->pub.color_quantize = quantize3_ord_dither; 
    else 
      cquantize->pub.color_quantize = quantize_ord_dither; 
    cquantize->row_index = 0;	/* initialize state for ordered dither */ 
    /* If user changed to ordered dither from another mode, 
     * we must recreate the color index table with padding. 
     * This will cost extra space, but probably isn't very likely. 
     */ 
    if (! cquantize->is_padded) 
      create_colorindex(cinfo); 
    /* Create ordered-dither tables if we didn't already. */ 
    if (cquantize->odither[0] == NULL) 
      create_odither_tables(cinfo); 
    break; 
  case JDITHER_FS: 
    cquantize->pub.color_quantize = quantize_fs_dither; 
    cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */ 
    /* Allocate Floyd-Steinberg workspace if didn't already. */ 
    if (cquantize->fserrors[0] == NULL) 
      alloc_fs_workspace(cinfo); 
    /* Initialize the propagated errors to zero. */ 
    arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR)); 
    for (i = 0; i < cinfo->out_color_components; i++) 
      jzero_far((void FAR *) cquantize->fserrors[i], arraysize); 
    break; 
  default: 
    ERREXIT(cinfo, JERR_NOT_COMPILED); 
    break; 
  } 
} 
 
 
/* 
 * Finish up at the end of the pass. 
 */ 
 
METHODDEF(void) 
finish_pass_1_quant (j_decompress_ptr cinfo) 
{ 
  /* no work in 1-pass case */ 
} 
 
 
/* 
 * Switch to a new external colormap between output passes. 
 * Shouldn't get to this module! 
 */ 
 
METHODDEF(void) 
new_color_map_1_quant (j_decompress_ptr cinfo) 
{ 
  ERREXIT(cinfo, JERR_MODE_CHANGE); 
} 
 
 
/* 
 * Module initialization routine for 1-pass color quantization. 
 */ 
 
GLOBAL(void) 
jinit_1pass_quantizer (j_decompress_ptr cinfo) 
{ 
  my_cquantize_ptr cquantize; 
 
  cquantize = (my_cquantize_ptr) 
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				SIZEOF(my_cquantizer)); 
  cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize; 
  cquantize->pub.start_pass = start_pass_1_quant; 
  cquantize->pub.finish_pass = finish_pass_1_quant; 
  cquantize->pub.new_color_map = new_color_map_1_quant; 
  cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */ 
  cquantize->odither[0] = NULL;	/* Also flag odither arrays not allocated */ 
 
  /* Make sure my internal arrays won't overflow */ 
  if (cinfo->out_color_components > MAX_Q_COMPS) 
    ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS); 
  /* Make sure colormap indexes can be represented by JSAMPLEs */ 
  if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1)) 
    ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1); 
 
  /* Create the colormap and color index table. */ 
  create_colormap(cinfo); 
  create_colorindex(cinfo); 
 
  /* Allocate Floyd-Steinberg workspace now if requested. 
   * We do this now since it is FAR storage and may affect the memory 
   * manager's space calculations.  If the user changes to FS dither 
   * mode in a later pass, we will allocate the space then, and will 
   * possibly overrun the max_memory_to_use setting. 
   */ 
  if (cinfo->dither_mode == JDITHER_FS) 
    alloc_fs_workspace(cinfo); 
} 
 
#endif /* QUANT_1PASS_SUPPORTED */