/*
* Reduce the image (bit depth + color type + palette) without
* losing any information. The palette (if applicable) and the
* image data must be present (e.g. by calling png_set_rows(),
* or by loading IDAT).
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
png_uint_32 PNGAPI
opng_reduce_image(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
unsigned int color_type;
png_uint_32 result;
png_debug(1, "in opng_reduce_image_type\n");
if (!opng_validate_image(png_ptr, info_ptr))
{
png_warning(png_ptr,
"Image reduction requires the presence of the critical info");
return OPNG_REDUCE_NONE;
}
#if 0 /* PNG_INTERLACE must be recognized! */
if (png_ptr->transformations)
{
png_warning(png_ptr,
"Image reduction cannot be applied "
"under the presence of transformations");
return OPNG_REDUCE_NONE;
}
#endif
color_type = info_ptr->color_type;
/* The reductions below must be applied in the given order. */
/* Try to reduce the high bits and color/alpha channels. */
result = opng_reduce_bits(png_ptr, info_ptr, reductions);
/* Try to reduce the palette image. */
if (color_type == PNG_COLOR_TYPE_PALETTE &&
(reductions & (OPNG_REDUCE_PALETTE_TO_GRAY |
OPNG_REDUCE_PALETTE_FAST |
OPNG_REDUCE_8_TO_4_2_1)))
result |= opng_reduce_palette(png_ptr, info_ptr, reductions);
/* Try to reduce RGB to palette or grayscale to palette. */
if (((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_GRAY &&
(reductions & OPNG_REDUCE_GRAY_TO_PALETTE)) ||
((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_RGB &&
(reductions & OPNG_REDUCE_RGB_TO_PALETTE)))
{
if (!(result & OPNG_REDUCE_PALETTE_TO_GRAY))
result |= opng_reduce_to_palette(png_ptr, info_ptr, reductions);
}
return result;
}
/*
* Imports an image from an PNG file stream.
* The function returns 0 on success or -1 on error.
*/
int opng_decode_image(struct opng_codec_context *context, FILE *stream, const char *fname, bool force_no_palette)
{
context->libpng_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, opng_read_error, opng_read_warning);
context->info_ptr = png_create_info_struct(context->libpng_ptr);
if (!context->libpng_ptr || !context->info_ptr)
{
opng_error(0, "Out of memory");
png_destroy_read_struct(&context->libpng_ptr, &context->info_ptr, 0);
exit(1);
}
opng_init_image(context->image);
const char * volatile err_msg; /* volatile is required by cexcept */
struct opng_encoding_stats * stats = context->stats;
opng_init_stats(stats);
context->stream = stream;
context->fname = fname;
if (force_no_palette) {
png_set_palette_to_rgb(context->libpng_ptr);
}
Try
{
png_set_keep_unknown_chunks(context->libpng_ptr, PNG_HANDLE_CHUNK_ALWAYS, 0, 0);
png_set_read_fn(context->libpng_ptr, context, opng_read_data);
png_read_png(context->libpng_ptr, context->info_ptr, 0, 0);
}
Catch (err_msg)
{
if (opng_validate_image(context->libpng_ptr, context->info_ptr))
{
/* The critical image info has already been loaded.
* Treat this error as a warning in order to allow data recovery.
*/
opng_warning(fname, err_msg);
}
else
{
opng_error(fname, err_msg);
return -1;
}
}
opng_load_image(context->image, context->libpng_ptr, context->info_ptr);
return 0;
}
/*
* Reduce the image (bit depth + color type + palette) without
* losing any information. The palette (if applicable) and the
* image data must be present, e.g., by calling png_set_rows(),
* or by loading IDAT.
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
png_uint_32 PNGAPI opng_reduce_image(png_structp png_ptr, png_infop info_ptr, png_uint_32 reductions)
{
if (!opng_validate_image(png_ptr, info_ptr))
{
png_warning(png_ptr, "Image reduction requires the presence of all critical information");
return OPNG_REDUCE_NONE;
}
int color_type = png_get_color_type(png_ptr, info_ptr);
/* The reductions below must be applied in this particular order. */
png_uint_32 result = 0;
if ((color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
&& (reductions & OPNG_REDUCE_DIRTY_ALPHA)
)
{result |= opng_reduce_dirty_alpha(png_ptr, info_ptr);}
/* Try to reduce the high bits and color/alpha channels. */
result |= opng_reduce_bits(png_ptr, info_ptr, reductions);
/* Try to reduce the palette image. */
if (color_type == PNG_COLOR_TYPE_PALETTE &&
(reductions &
(OPNG_REDUCE_PALETTE_TO_GRAY |
OPNG_REDUCE_PALETTE_FAST |
OPNG_REDUCE_8_TO_4_2_1)))
result |= opng_reduce_palette(png_ptr, info_ptr, reductions);
/* Try to reduce RGB to palette or grayscale to palette. */
if (((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_GRAY &&
(reductions & OPNG_REDUCE_GRAY_TO_PALETTE)) ||
((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_RGB &&
(reductions & OPNG_REDUCE_RGB_TO_PALETTE)))
{
if (!(result & OPNG_REDUCE_PALETTE_TO_GRAY))
result |= opng_reduce_to_palette(png_ptr, info_ptr, reductions);
}
return result;
}
