/*
* Reduce the palette (only the fast method is implemented).
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
png_uint_32 /* PRIVATE */
opng_reduce_palette(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_uint_32 result;
png_colorp palette;
png_bytep trans_alpha;
png_bytepp rows;
png_uint_32 width, height, i, j;
png_byte is_used[256];
int num_palette, num_trans, last_color_index, last_trans_index, is_gray, k;
png_color_16 gray_trans;
png_byte crt_trans_value, last_trans_value;
opng_debug(1, "in opng_reduce_palette");
height = info_ptr->height;
width = info_ptr->width;
palette = info_ptr->palette;
num_palette = info_ptr->num_palette;
rows = info_ptr->row_pointers;
if (info_ptr->valid & PNG_INFO_tRNS)
{
trans_alpha = info_ptr->trans_alpha;
num_trans = info_ptr->num_trans;
OPNG_ASSERT(trans_alpha != NULL && num_trans > 0);
}
else
{
trans_alpha = NULL;
num_trans = 0;
}
/* Analyze the possible reductions. */
/* Also check the integrity of PLTE and tRNS. */
opng_analyze_sample_usage(png_ptr, info_ptr, is_used);
/* Palette-to-gray does not work (yet) if the bit depth is below 8. */
is_gray = (reductions & OPNG_REDUCE_PALETTE_TO_GRAY) &&
(info_ptr->bit_depth == 8);
last_color_index = last_trans_index = -1;
for (k = 0; k < 256; ++k)
{
if (!is_used[k])
continue;
last_color_index = k;
if (k < num_trans && trans_alpha[k] < 255)
last_trans_index = k;
if (is_gray)
if (palette[k].red != palette[k].green ||
palette[k].red != palette[k].blue)
is_gray = 0;
}
OPNG_ASSERT(last_color_index >= 0);
if (last_color_index >= num_palette)
{
png_warning(png_ptr, "Too few colors in palette");
/* Fix the palette by adding blank entries at the end. */
num_palette = last_color_index + 1;
info_ptr->num_palette = (png_uint_16)num_palette;
}
if (num_trans > num_palette)
{
png_warning(png_ptr, "Too many alpha values in tRNS");
info_ptr->num_trans = info_ptr->num_palette;
}
num_trans = last_trans_index + 1;
OPNG_ASSERT(num_trans <= num_palette);
/* Check if tRNS can be reduced to grayscale. */
if (is_gray && num_trans > 0)
{
gray_trans.gray = palette[last_trans_index].red;
last_trans_value = trans_alpha[last_trans_index];
for (k = 0; k <= last_color_index; ++k)
{
if (!is_used[k])
continue;
if (k <= last_trans_index)
{
crt_trans_value = trans_alpha[k];
/* Cannot reduce if different colors have transparency. */
if (crt_trans_value < 255 && palette[k].red != gray_trans.gray)
{
is_gray = 0;
break;
}
}
else
crt_trans_value = 255;
/* Cannot reduce if same color has multiple transparency levels. */
if (palette[k].red == gray_trans.gray &&
crt_trans_value != last_trans_value)
{
is_gray = 0;
break;
}
}
}
/* Initialize result value. */
result = OPNG_REDUCE_NONE;
/* Remove tRNS if possible. */
if ((info_ptr->valid & PNG_INFO_tRNS) && num_trans == 0)
{
png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, -1);
info_ptr->valid &= ~PNG_INFO_tRNS;
result = OPNG_REDUCE_PALETTE_FAST;
}
if (reductions & OPNG_REDUCE_PALETTE_FAST)
{
if (num_palette != last_color_index + 1)
{
/* Reduce PLTE. */
/* hIST is reduced automatically. */
info_ptr->num_palette = (png_uint_16)(last_color_index + 1);
result = OPNG_REDUCE_PALETTE_FAST;
}
if ((info_ptr->valid & PNG_INFO_tRNS) &&
(int)info_ptr->num_trans != num_trans)
{
/* Reduce tRNS. */
info_ptr->num_trans = (png_uint_16)num_trans;
result = OPNG_REDUCE_PALETTE_FAST;
}
}
if (reductions & OPNG_REDUCE_8_TO_4_2_1)
result |= opng_reduce_palette_bits(png_ptr, info_ptr, reductions);
if (info_ptr->bit_depth < 8 || !is_gray)
return result;
/* Reduce palette -> grayscale. */
for (i = 0; i < height; ++i)
for (j = 0; j < width; ++j)
rows[i][j] = palette[rows[i][j]].red;
#if defined(PNG_bKGD_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
/* Update the ancillary chunk info. */
if (info_ptr->valid & PNG_INFO_bKGD)
info_ptr->background.gray = palette[info_ptr->background.index].red;
#endif
#if defined(PNG_hIST_SUPPORTED)
if (info_ptr->valid & PNG_INFO_hIST)
{
png_free_data(png_ptr, info_ptr, PNG_FREE_HIST, -1);
info_ptr->valid &= ~PNG_INFO_hIST;
}
#endif
#if defined(PNG_sBIT_SUPPORTED)
if (info_ptr->valid & PNG_INFO_sBIT)
{
png_color_8p sig_bit_ptr = &info_ptr->sig_bit;
png_byte max_sig_bit = sig_bit_ptr->red;
if (max_sig_bit < sig_bit_ptr->green)
max_sig_bit = sig_bit_ptr->green;
if (max_sig_bit < sig_bit_ptr->blue)
max_sig_bit = sig_bit_ptr->blue;
png_ptr->sig_bit.gray = info_ptr->sig_bit.gray = max_sig_bit;
}
#endif
if (info_ptr->valid & PNG_INFO_tRNS)
png_set_tRNS(png_ptr, info_ptr, NULL, 0, &gray_trans);
/* Update the image info. */
png_ptr->rowbytes = info_ptr->rowbytes = 0;
png_ptr->color_type = info_ptr->color_type = PNG_COLOR_TYPE_GRAY;
png_free_data(png_ptr, info_ptr, PNG_FREE_PLTE, -1);
info_ptr->valid &= ~PNG_INFO_PLTE;
return OPNG_REDUCE_PALETTE_TO_GRAY; /* ignore the former result */
}
/*
* Reduce the palette. (Only the fast method is implemented.)
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
static png_uint_32 opng_reduce_palette(png_structp png_ptr, png_infop info_ptr, png_uint_32 reductions)
{
png_colorp palette;
png_bytep trans_alpha;
png_uint_32 width, height;
int bit_depth, color_type, interlace_type, compression_type, filter_type;
int num_palette, num_trans;
int last_color_index, last_trans_index;
png_byte crt_trans_value, last_trans_value;
png_byte is_used[256];
png_color_16 gray_trans;
png_uint_32 result = OPNG_REDUCE_NONE;
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,
&color_type, &interlace_type, &compression_type, &filter_type);
if (!height || !width){
return OPNG_REDUCE_NONE;
}
png_bytepp row_ptr = png_get_rows(png_ptr, info_ptr);
if (!png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))
{
palette = 0;
num_palette = 0;
}
if (!png_get_tRNS(png_ptr, info_ptr, &trans_alpha, &num_trans, 0))
{
trans_alpha = 0;
num_trans = 0;
}
else
OPNG_ASSERT(trans_alpha && num_trans > 0);
opng_analyze_sample_usage(png_ptr, info_ptr, is_used);
/* Palette-to-gray does not work (yet) if the bit depth is below 8. */
int is_gray = (reductions & OPNG_REDUCE_PALETTE_TO_GRAY) && (bit_depth == 8);
last_color_index = last_trans_index = -1;
int k;
for (k= 0; k < 256; ++k)
{
if (!is_used[k])
continue;
last_color_index = k;
if (k < num_trans && trans_alpha[k] < 255)
last_trans_index = k;
if (is_gray)
if (palette[k].red != palette[k].green ||
palette[k].red != palette[k].blue)
is_gray = 0;
}
OPNG_ASSERT(last_color_index >= 0);
OPNG_ASSERT(last_color_index >= last_trans_index);
/* Check the integrity of PLTE and tRNS. */
if (last_color_index >= num_palette)
{
png_warning(png_ptr, "Too few colors in PLTE");
/* Fix the palette by adding blank entries at the end. */
opng_realloc_PLTE(png_ptr, info_ptr, last_color_index + 1);
png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
OPNG_ASSERT(num_palette == last_color_index + 1);
result |= OPNG_REDUCE_REPAIR;
}
if (num_trans > num_palette)
{
png_warning(png_ptr, "Too many alpha values in tRNS");
/* Transparency will be fixed further below. */
result |= OPNG_REDUCE_REPAIR;
}
/* Check if tRNS can be reduced to grayscale. */
if (is_gray && last_trans_index >= 0)
{
gray_trans.gray = palette[last_trans_index].red;
last_trans_value = trans_alpha[last_trans_index];
for (k = 0; k <= last_color_index; ++k)
{
if (!is_used[k])
continue;
if (k <= last_trans_index)
{
crt_trans_value = trans_alpha[k];
/* Cannot reduce if different colors have transparency. */
if (crt_trans_value < 255 && palette[k].red != gray_trans.gray)
{
is_gray = 0;
break;
}
}
else
crt_trans_value = 255;
/* Cannot reduce if same color has multiple transparency levels. */
if (palette[k].red == gray_trans.gray &&
crt_trans_value != last_trans_value)
{
is_gray = 0;
break;
}
}
}
/* Remove tRNS if it is entirely sterile. */
if (num_trans > 0 && last_trans_index < 0)
{
num_trans = 0;
png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_tRNS);
result |= OPNG_REDUCE_PALETTE_FAST;
}
if (reductions & OPNG_REDUCE_PALETTE_FAST)
{
if (num_palette != last_color_index + 1)
{
/* Reduce PLTE. */
/* hIST is reduced automatically. */
opng_realloc_PLTE(png_ptr, info_ptr, last_color_index + 1);
png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
OPNG_ASSERT(num_palette == last_color_index + 1);
result |= OPNG_REDUCE_PALETTE_FAST;
}
if (num_trans > 0 && num_trans != last_trans_index + 1)
{
/* Reduce tRNS. */
opng_realloc_tRNS(png_ptr, info_ptr, last_trans_index + 1);
png_get_tRNS(png_ptr, info_ptr, &trans_alpha, &num_trans, 0);
OPNG_ASSERT(num_trans == last_trans_index + 1);
result |= OPNG_REDUCE_PALETTE_FAST;
}
}
if (reductions & OPNG_REDUCE_8_TO_4_2_1)
{
result |= opng_reduce_palette_bits(png_ptr, info_ptr, reductions);
/* Refresh the image information. */
bit_depth = png_get_bit_depth(png_ptr, info_ptr);
}
if ((bit_depth < 8) || !is_gray)
return result;
/* Reduce palette --> grayscale. */
for (png_uint_32 i = 0; i < height; ++i)
{
for (png_uint_32 j = 0; j < width; ++j)
row_ptr[i][j] = palette[row_ptr[i][j]].red;
}
/* Update the ancillary information. */
if (num_trans > 0)
png_set_tRNS(png_ptr, info_ptr, 0, 0, &gray_trans);
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
if (png_get_bKGD(png_ptr, info_ptr, &background))
background->gray = palette[background->index].red;
#endif
#ifdef PNG_hIST_SUPPORTED
png_uint_16p hist;
if (png_get_hIST(png_ptr, info_ptr, &hist))
{
png_free_data(png_ptr, info_ptr, PNG_FREE_HIST, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_hIST);
}
#endif
#ifdef PNG_sBIT_SUPPORTED
png_color_8p sig_bits;
if (png_get_sBIT(png_ptr, info_ptr, &sig_bits))
{
png_byte max_sig_bits = sig_bits->red;
if (max_sig_bits < sig_bits->green)
max_sig_bits = sig_bits->green;
if (max_sig_bits < sig_bits->blue)
max_sig_bits = sig_bits->blue;
sig_bits->gray = max_sig_bits;
}
#endif
/* Update the image information. */
png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
PNG_COLOR_TYPE_GRAY, interlace_type, compression_type, filter_type);
png_free_data(png_ptr, info_ptr, PNG_FREE_PLTE, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_PLTE);
return OPNG_REDUCE_PALETTE_TO_GRAY; /* ignore the former result */
}
