jquant1.pas

DELPHI版的JPEG文件解码源程序

  for i := 0 to pred(cinfo^.out_color_components) do
  begin
    { fill in colormap entries for i'th color component }
    nci := cquantize^.Ncolors[i]; { # of distinct values for this color }
    blksize := blkdist div nci;
    for j := 0 to pred(nci) do
    begin
      { 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 }
      ptr := j * blksize;
      while (ptr < total_colors) do
      begin
	{ fill in blksize entries beginning at ptr }
	for k := 0 to pred(blksize) do
          colormap^[i]^[ptr+k] := JSAMPLE(val);

        Inc(ptr, blkdist);
      end;
    end;
    blkdist := blksize;		{ blksize of this color is blkdist of next }
  end;

  { Save the colormap in private storage,
    where it will survive color quantization mode changes. }

  cquantize^.sv_colormap := colormap;
  cquantize^.sv_actual := total_colors;
end;

{ Create the color index table. }

{LOCAL}
procedure create_colorindex (cinfo : j_decompress_ptr);
var
  cquantize : my_cquantize_ptr;
  indexptr,
  help_indexptr : JSAMPROW;  { for negative offsets }
  i,j,k, nci, blksize, val, pad : int;
begin
  cquantize := my_cquantize_ptr (cinfo^.cquantize);
  { 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) then
  begin
    pad := MAXJSAMPLE*2;
    cquantize^.is_padded := TRUE;
  end
  else
  begin
    pad := 0;
    cquantize^.is_padded := FALSE;
  end;

  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 to pred(cinfo^.out_color_components) do
  begin
    { fill in colorindex entries for i'th color component }
    nci := cquantize^.Ncolors[i]; { # of distinct values for this color }
    blksize := blksize div nci;

    { adjust colorindex pointers to provide padding at negative indexes. }
    if (pad <> 0) then
      Inc(JSAMPLE_PTR(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 to MAXJSAMPLE do
    begin
      while (j > k) do          { advance val if past boundary }
      begin
        Inc(val);
	k := largest_input_value(cinfo, i, val, nci-1);
      end;
      { premultiply so that no multiplication needed in main processing }
      indexptr^[j] := JSAMPLE (val * blksize);
    end;
    { Pad at both ends if necessary }
    if (pad <> 0) then
    begin
      help_indexptr := indexptr;
      { adjust the help pointer to avoid negative offsets }
      Dec(JSAMPLE_PTR(help_indexptr), MAXJSAMPLE);

      for j := 1 to MAXJSAMPLE do
      begin
        {indexptr^[-j] := indexptr^[0];}
        help_indexptr^[MAXJSAMPLE-j] := indexptr^[0];
        indexptr^[MAXJSAMPLE+j] := indexptr^[MAXJSAMPLE];
      end;
    end;
  end;
end;


{ Create an ordered-dither array for a component having ncolors
  distinct output values. }

{LOCAL}
function make_odither_array (cinfo : j_decompress_ptr;
                             ncolors : int) : ODITHER_MATRIX_PTR;
var
  odither : ODITHER_MATRIX_PTR;
  j, k : int;
  num, den : INT32;
begin
  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 * ( INT32(ncolors - 1));
  for j := 0 to pred(ODITHER_SIZE) do
  begin
    for k := 0 to pred(ODITHER_SIZE) do
    begin
      num := ( 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... }

      if num<0 then
        odither^[j][k] := int (-((-num) div den))
      else
        odither^[j][k] := int (num div den);
    end;
  end;
  make_odither_array := odither;
end;


{ Create the ordered-dither tables.
  Components having the same number of representative colors may
  share a dither table. }

{LOCAL}
procedure create_odither_tables (cinfo : j_decompress_ptr);
var
  cquantize : my_cquantize_ptr;
  odither : ODITHER_MATRIX_PTR;
  i, j, nci : int;
begin
  cquantize := my_cquantize_ptr (cinfo^.cquantize);

  for i := 0 to pred(cinfo^.out_color_components) do
  begin
    nci := cquantize^.Ncolors[i]; { # of distinct values for this color }
    odither := NIL;		  { search for matching prior component }
    for j := 0 to pred(i) do
    begin
      if (nci = cquantize^.Ncolors[j]) then
      begin
	odither := cquantize^.odither[j];
	break;
      end;
    end;
    if (odither = NIL)	then { need a new table? }
      odither := make_odither_array(cinfo, nci);
    cquantize^.odither[i] := odither;
  end;
end;


{ Map some rows of pixels to the output colormapped representation. }

{METHODDEF}
procedure color_quantize (cinfo : j_decompress_ptr;
                          input_buf : JSAMPARRAY;
		          output_buf : JSAMPARRAY;
                          num_rows : int); far;
{ General case, no dithering }
var
  cquantize : my_cquantize_ptr;
  colorindex : JSAMPARRAY;
  pixcode, ci : int; {register}
  ptrin, ptrout : JSAMPLE_PTR; {register}
  row : int;
  col : JDIMENSION;
  width : JDIMENSION;
  nc : int; {register}
begin
  cquantize := my_cquantize_ptr (cinfo^.cquantize);
  colorindex := cquantize^.colorindex;
  width := cinfo^.output_width;
  nc := cinfo^.out_color_components;

  for row := 0 to pred(num_rows) do
  begin
    ptrin := JSAMPLE_PTR(input_buf^[row]);
    ptrout := JSAMPLE_PTR(output_buf^[row]);
    for col := pred(width) downto 0 do
    begin
      pixcode := 0;
      for ci := 0 to pred(nc) do
      begin
	Inc(pixcode, GETJSAMPLE(colorindex^[ci]^[GETJSAMPLE(ptrin^)]) );
        Inc(ptrin);
      end;
      ptrout^ := JSAMPLE (pixcode);
      Inc(ptrout);
    end;
  end;
end;


{METHODDEF}
procedure color_quantize3 (cinfo : j_decompress_ptr;
                           input_buf : JSAMPARRAY;
		           output_buf : JSAMPARRAY;
                           num_rows : int); far;
{ Fast path for out_color_components=3, no dithering }
var
  cquantize : my_cquantize_ptr;
  pixcode : int; {register}
  ptrin, ptrout : JSAMPLE_PTR; {register}
  colorindex0 : JSAMPROW;
  colorindex1 : JSAMPROW;
  colorindex2 : JSAMPROW;
  row : int;
  col : JDIMENSION;
  width : JDIMENSION;
begin
  cquantize := my_cquantize_ptr (cinfo^.cquantize);
  colorindex0 := (cquantize^.colorindex)^[0];
  colorindex1 := (cquantize^.colorindex)^[1];
  colorindex2 := (cquantize^.colorindex)^[2];
  width := cinfo^.output_width;

  for row := 0 to pred(num_rows) do
  begin
    ptrin := JSAMPLE_PTR(input_buf^[row]);
    ptrout := JSAMPLE_PTR(output_buf^[row]);
    for col := pred(width) downto 0 do
    begin
      pixcode  := GETJSAMPLE((colorindex0)^[GETJSAMPLE(ptrin^)]);
      Inc(ptrin);
      Inc( pixcode, GETJSAMPLE((colorindex1)^[GETJSAMPLE(ptrin^)]) );
      Inc(ptrin);
      Inc( pixcode, GETJSAMPLE((colorindex2)^[GETJSAMPLE(ptrin^)]) );
      Inc(ptrin);
      ptrout^ := JSAMPLE (pixcode);
      Inc(ptrout);
    end;
  end;
end;


{METHODDEF}
procedure quantize_ord_dither (cinfo : j_decompress_ptr;
                               input_buf :  JSAMPARRAY;
		               output_buf : JSAMPARRAY;
                               num_rows : int); far;
{ General case, with ordered dithering }
var
  cquantize : my_cquantize_ptr;
  input_ptr,                {register}
  output_ptr : JSAMPLE_PTR; {register}
  colorindex_ci : JSAMPROW;
  dither : ^ODITHER_vector;     { points to active row of dither matrix }
  row_index, col_index : int;   { current indexes into dither matrix }
  nc : int;
  ci : int;
  row : int;
  col : JDIMENSION;
  width : JDIMENSION;
var
  pad_offset : int;
begin
  cquantize := my_cquantize_ptr (cinfo^.cquantize);
  nc := cinfo^.out_color_components;
  width := cinfo^.output_width;

  { Nomssi: work around negative offset }
  if my_cquantize_ptr (cinfo^.cquantize)^.is_padded then
    pad_offset := MAXJSAMPLE
  else
    pad_offset := 0;

  for row := 0 to pred(num_rows) do
  begin
    { Initialize output values to 0 so can process components separately }
    jzero_far( {far} pointer(output_buf^[row]),
	      size_t(width * SIZEOF(JSAMPLE)));
    row_index := cquantize^.row_index;
    for ci := 0 to pred(nc) do
    begin
      input_ptr := JSAMPLE_PTR(@ input_buf^[row]^[ci]);
      output_ptr := JSAMPLE_PTR(output_buf^[row]);
      colorindex_ci := cquantize^.colorindex^[ci];
      { Nomssi }
      Dec(JSAMPLE_PTR(colorindex_ci), pad_offset);

      dither := @(cquantize^.odither[ci]^[row_index]);
      col_index := 0;

      for col := pred(width) downto 0 do
      begin
	{ 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. }

	Inc(output_ptr^,
            colorindex_ci^[GETJSAMPLE(input_ptr^)+ pad_offset +
                                         dither^[col_index]]);
        Inc(output_ptr);
	Inc(input_ptr, nc);
	col_index := (col_index + 1) and ODITHER_MASK;
      end;
    end;
    { Advance row index for next row }
    row_index := (row_index + 1) and ODITHER_MASK;
    cquantize^.row_index := row_index;
  end;
end;

{METHODDEF}
procedure quantize3_ord_dither (cinfo : j_decompress_ptr;