[devel] Added png_set_chop_16() API.
diff --git a/pngrtran.c b/pngrtran.c
index 4ed4b4c..867145f 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -133,7 +133,7 @@
#endif /* READ_BACKGROUND */
#ifdef PNG_READ_16_TO_8_SUPPORTED
-/* Strip 16-bit depth files to 8-bit depth */
+/* Scale 16-bit depth files to 8-bit depth */
void PNGAPI
png_set_strip_16(png_structp png_ptr)
{
@@ -143,6 +143,20 @@
return;
png_ptr->transformations |= PNG_16_TO_8;
+ png_ptr->transformations &= ~PNG_CHOP_16_TO_8;
+}
+
+/* Chop 16-bit depth files to 8-bit depth */
+void PNGAPI
+png_set_chop_16(png_structp png_ptr)
+{
+ png_debug(1, "in png_set_chop_16");
+
+ if (png_ptr == NULL)
+ return;
+
+ png_ptr->transformations |= PNG_CHOP_16_TO_8;
+ png_ptr->transformations &= ~PNG_16_TO_8;
}
#endif
@@ -1312,7 +1326,7 @@
* 6) PNG_GAMMA
* 7) PNG_STRIP_ALPHA (if compose)
* 8) PNG_ENCODE_ALPHA
- * 9) PNG_16_TO_8 (strip16)
+ * 9) PNG_16_TO_8 or PNG_CHOP_16_TO_8 (strip16/chop16)
* 10) PNG_QUANTIZE (converts to palette)
* 11) PNG_EXPAND_16
* 12) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
@@ -1851,13 +1865,15 @@
#ifdef PNG_READ_16_TO_8_SUPPORTED
#ifdef PNG_READ_16BIT_SUPPORTED
- if ((png_ptr->transformations & PNG_16_TO_8) && (info_ptr->bit_depth == 16))
+ if ((png_ptr->transformations & (PNG_16_TO_8 | PNG_CHOP_16_TO_8)) &&
+ (info_ptr->bit_depth == 16))
info_ptr->bit_depth = 8;
#else
/* Force chopping 16-bit input down to 8 */
if (info_ptr->bit_depth == 16)
{
- png_ptr->transformations |=PNG_16_TO_8;
+ if (!(png_ptr->transformations & PNG_CHOP_16_TO_8))
+ png_ptr->transformations |=PNG_16_TO_8;
info_ptr->bit_depth = 8;
}
#endif
@@ -2123,6 +2139,8 @@
#ifdef PNG_READ_16_TO_8_SUPPORTED
if (png_ptr->transformations & PNG_16_TO_8)
+ png_do_scale_16_to_8(&(png_ptr->row_info), png_ptr->row_buf + 1);
+ else if (png_ptr->transformations & PNG_CHOP_16_TO_8)
png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif
@@ -2453,11 +2471,11 @@
#endif
#ifdef PNG_READ_16_TO_8_SUPPORTED
-/* Chop rows of bit depth 16 down to 8 */
+/* Scale rows of bit depth 16 down to 8 accurately */
void /* PRIVATE */
-png_do_chop(png_row_infop row_info, png_bytep row)
+png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
{
- png_debug(1, "in png_do_chop");
+ png_debug(1, "in png_do_scale_16_to_8");
if (row_info->bit_depth == 16)
{
@@ -2500,15 +2518,7 @@
*/
png_int_32 tmp = *sp++; /* must be signed! */
-#ifdef PNG_LEGACY_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
- tmp += (((int)*sp++ - tmp) > 128) ? 1 : 0;
-#else
-# ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
-# else
- sp++;
-# endif
-#endif
*dp++ = (png_byte)tmp;
}
@@ -2517,7 +2527,33 @@
row_info->rowbytes = row_info->width * row_info->channels;
}
}
-#endif
+
+void /* PRIVATE */
+/* Simply discard the low byte. This was the default behavior prior
+ * to libpng-1.5.4.
+ */
+png_do_chop(png_row_infop row_info, png_bytep row)
+{
+ png_debug(1, "in png_do_chop");
+
+ if (row_info->bit_depth == 16)
+ {
+ png_bytep sp = row; /* source */
+ png_bytep dp = row; /* destinaton */
+ png_bytep ep = sp + row_info->rowbytes; /* end+1 */
+
+ while (sp < ep)
+ {
+ *dp++ = *sp++;
+ sp++;
+ }
+
+ row_info->bit_depth = 8;
+ row_info->pixel_depth = (png_byte)(8 * row_info->channels);
+ row_info->rowbytes = row_info->width * row_info->channels;
+ }
+}
+#endif /* PNG_READ_16_TO_8_SUPPORTED */
#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
void /* PRIVATE */
