[devel] Added named value and 'flag' gamma support to png_set_gamma. Made a
minor change from the previous (unreleased) ABI/API to hide the exact value
used for Macs - it's not a good idea to embed this in the ABI!
diff --git a/ANNOUNCE b/ANNOUNCE
index 6663232..23c6d6b 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
-Libpng 1.5.3beta07 - May 9, 2011
+Libpng 1.5.3beta07 - May 11, 2011
This is not intended to be a public release. It will be replaced
within a few weeks by a public version or by another test version.
@@ -101,8 +101,11 @@
Removed the -D_ALL_SOURCE from definitions for AIX in CMakeLists.txt
Implemented premultiplied alpha support: png_set_alpha_mode API
-Version 1.5.3beta07 [May 9, 2011]
+Version 1.5.3beta07 [May 11, 2011]
Added expand_16 support to the high level interface.
+ Added named value and 'flag' gamma support to png_set_gamma. Made a minor
+ change from the previous (unreleased) ABI/API to hide the exact value used
+ for Macs - it's not a good idea to embed this in the ABI!
Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
(subscription required; visit
diff --git a/CHANGES b/CHANGES
index d40d01a..6ed3dd6 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3360,8 +3360,11 @@
Removed the -D_ALL_SOURCE from definitions for AIX in CMakeLists.txt
Implemented premultiplied alpha support: png_set_alpha_mode API
-Version 1.5.3beta07 [May 9, 2011]
+Version 1.5.3beta07 [May 11, 2011]
Added expand_16 support to the high level interface.
+ Added named value and 'flag' gamma support to png_set_gamma. Made a minor
+ change from the previous (unreleased) ABI/API to hide the exact value used
+ for Macs - it's not a good idea to embed this in the ABI!
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit
diff --git a/png.h b/png.h
index fb188d7..19a9296 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
/* png.h - header file for PNG reference library
*
- * libpng version 1.5.3beta07 - May 9, 2011
+ * libpng version 1.5.3beta07 - May 11, 2011
* Copyright (c) 1998-2011 Glenn Randers-Pehrson
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -11,7 +11,7 @@
* Authors and maintainers:
* libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
* libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- * libpng versions 0.97, January 1998, through 1.5.3beta07 - May 9, 2011: Glenn
+ * libpng versions 0.97, January 1998, through 1.5.3beta07 - May 11, 2011: Glenn
* See also "Contributing Authors", below.
*
* Note about libpng version numbers:
@@ -182,7 +182,7 @@
*
* This code is released under the libpng license.
*
- * libpng versions 1.2.6, August 15, 2004, through 1.5.3beta07, May 9, 2011, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.5.3beta07, May 11, 2011, are
* Copyright (c) 2004, 2006-2011 Glenn Randers-Pehrson, and are
* distributed according to the same disclaimer and license as libpng-1.2.5
* with the following individual added to the list of Contributing Authors:
@@ -294,7 +294,7 @@
* Y2K compliance in libpng:
* =========================
*
- * May 9, 2011
+ * May 11, 2011
*
* Since the PNG Development group is an ad-hoc body, we can't make
* an official declaration.
@@ -357,7 +357,7 @@
/* Version information for png.h - this should match the version in png.c */
#define PNG_LIBPNG_VER_STRING "1.5.3beta07"
#define PNG_HEADER_VERSION_STRING \
- " libpng version 1.5.3beta07 - May 9, 2011\n"
+ " libpng version 1.5.3beta07 - May 11, 2011\n"
#define PNG_LIBPNG_VER_SONUM 15
#define PNG_LIBPNG_VER_DLLNUM 15
@@ -1176,7 +1176,9 @@
double output_gamma));
PNG_FIXED_EXPORT(228, void, png_set_alpha_mode_fixed, (png_structp png_ptr,
int mode, png_fixed_point output_gamma));
+#endif
+#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_ALPHA_MODE_SUPPORTED)
/* The output_gamma value is a screen gamma in libpng terminology: it expresses
* how to decode the output values, not how they are encoded. The values used
* correspond to the normal numbers used to describe the overall gamma of a
@@ -1230,14 +1232,22 @@
* better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
* default if you don't know what the right answer is!
*
+ * The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
+ * 10.6) which used a correction table to implement a somewhat lower gamma on an
+ * otherwise sRGB system.
+ *
+ * Both these values are reserved (not simple gamma values) in order to allow
+ * more precise correction internally in the future.
+ *
* NOTE: the following values can be passed to either the fixed or floating
* point APIs, but the floating point API will also accept floating point
* values.
*/
-#define PNG_DEFAULT_sRGB 0 /* sRGB gamma and color space */
+#define PNG_DEFAULT_sRGB -1 /* sRGB gamma and color space */
+#define PNG_GAMMA_MAC_18 -2 /* Old Mac '1.8' gamma and color space */
#define PNG_GAMMA_sRGB 220000 /* Television standards--matches sRGB gamma */
-#define PNG_GAMMA_MAC 151724 /* Television with a 1.45 correction table */
#define PNG_GAMMA_LINEAR PNG_FP_1 /* Linear */
+#endif
/* The following are examples of calls to png_set_alpha_mode to achieve the
* required overall gamma correction and, where necessary, alpha
@@ -1314,7 +1324,6 @@
* made in the same read operation, however multiple calls with PNG_ALPHA_PNG
* are ignored.
*/
-#endif
#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
PNG_EXPORT(36, void, png_set_strip_alpha, (png_structp png_ptr));
@@ -1421,7 +1430,13 @@
/* Handle gamma correction. Screen_gamma=(display_exponent).
* NOTE: this API simply sets the screen and file gamma values. It will
* therefore override the value for gamma in a PNG file if it is called after
- * the file header has been read - use with care!
+ * the file header has been read - use with care - call before reading the PNG
+ * file for best results!
+ *
+ * These routines accept the same gamma values as png_set_alpha_mode (described
+ * above). The PNG_GAMMA_ defines and PNG_DEFAULT_sRGB can be passed to either
+ * API (floating point or fixed.) Notice, however, that the 'file_gamma' value
+ * is the inverse of a 'screen gamma' value.
*/
PNG_FP_EXPORT(50, void, png_set_gamma,
(png_structp png_ptr, double screen_gamma,
diff --git a/pngpriv.h b/pngpriv.h
index d6849c3..dfe0ca2 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -459,6 +459,11 @@
#define PNG_tRNS PNG_CONST png_byte png_tRNS[5] = {116, 82, 78, 83, '\0'}
#define PNG_zTXt PNG_CONST png_byte png_zTXt[5] = {122, 84, 88, 116, '\0'}
+/* Gamma values (new at libpng-1.5.3): */
+#define PNG_GAMMA_MAC_OLD 151724 /* Assume '1.8' is really 2.2/1.45! */
+#define PNG_GAMMA_MAC_INVERSE 65909
+#define PNG_GAMMA_sRGB_INVERSE 45455
+
/* Inhibit C++ name-mangling for libpng functions but not for system calls. */
#ifdef __cplusplus
diff --git a/pngrtran.c b/pngrtran.c
index cdf84ce..dda48c0 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -159,6 +159,68 @@
}
#endif
+#if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
+static png_fixed_point
+translate_gamma_flags(png_structp png_ptr, png_fixed_point output_gamma,
+ int is_screen)
+{
+ /* Check for flag values. The main reason for having the old Mac value as a
+ * flag is that it is pretty near impossible to work out what the correct
+ * value is from Apple documentation - a working Mac system is needed to
+ * discover the value!
+ */
+ if (output_gamma == PNG_DEFAULT_sRGB ||
+ output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
+ {
+ /* If there is no sRGB support this just sets the gamma to the standard
+ * sRGB value. (This is a side effect of using this function!)
+ */
+# ifdef PNG_READ_sRGB_SUPPORTED
+ png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
+# endif
+ if (is_screen)
+ output_gamma = PNG_GAMMA_sRGB;
+ else
+ output_gamma = PNG_GAMMA_sRGB_INVERSE;
+ }
+
+ else if (output_gamma == PNG_GAMMA_MAC_18 ||
+ output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
+ {
+ if (is_screen)
+ output_gamma = PNG_GAMMA_MAC_OLD;
+ else
+ output_gamma = PNG_GAMMA_MAC_INVERSE;
+ }
+
+ return output_gamma;
+}
+
+# ifdef PNG_FLOATING_POINT_SUPPORTED
+static png_fixed_point
+convert_gamma_value(png_structp png_ptr, double output_gamma)
+{
+ /* The following silently ignores cases where fixed point (times 100,000)
+ * gamma values are passed to the floating point API. This is safe and it
+ * means the fixed point constants work just fine with the floating point
+ * API. The alternative would just lead to undetected errors and spurious
+ * bug reports. Negative values fail inside the _fixed API unless they
+ * correspond to the flag values.
+ */
+ if (output_gamma > 0 && output_gamma < 128)
+ output_gamma *= PNG_FP_1;
+
+ /* This preserves -1 and -2 exactly: */
+ output_gamma = floor(output_gamma + .5);
+
+ if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
+ png_fixed_error(png_ptr, "gamma value");
+
+ return (png_fixed_point)output_gamma;
+}
+# endif
+#endif /* READ_ALPHA_MODE || READ_GAMMA */
+
#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
void PNGFAPI
png_set_alpha_mode_fixed(png_structp png_ptr, int mode,
@@ -172,28 +234,15 @@
if (png_ptr == NULL)
return;
- /* If the default_gamma value is 0 then switch on the whole sRGB
- * edifice by this flag (note: this is a flag to the later code,
- * not a transformation!)
- */
- if (output_gamma == PNG_DEFAULT_sRGB)
- {
- /* If there is no sRGB support this just sets the gamma to the standard
- * sRGB value.
- */
-# ifdef PNG_READ_sRGB_SUPPORTED
- png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
-# endif
- output_gamma = PNG_GAMMA_sRGB;
- }
+ output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
- /* Else validate the value to ensure it is in a reasonable range. The value
+ /* Validate the value to ensure it is in a reasonable range. The value
* is expected to be 1 or greater, but this range test allows for some
* viewing correction values. The intent is to weed out users of this API
* who use the inverse of the gamma value accidentally! Since some of these
* values are reasonable this may have to be changed.
*/
- else if (output_gamma < 70000 || output_gamma > 300000)
+ if (output_gamma < 70000 || output_gamma > 300000)
png_error(png_ptr, "output gamma out of expected range");
/* The default file gamma is the inverse of the output gamma; the output
@@ -286,19 +335,8 @@
void PNGAPI
png_set_alpha_mode(png_structp png_ptr, int mode, double output_gamma)
{
- /* The following silently ignores cases where fixed point (times 100,000)
- * gamma values are passed to the floating point API. This is safe and it
- * means the fixed point constants work just fine with the floating point
- * API. The alternative would just lead to undetected errors and spurious
- * bug reports. Negative values fail inside the _fixed API.
- */
- if (output_gamma > -128 && output_gamma < 128)
- output_gamma *= PNG_FP_1;
-
- if (output_gamma <= PNG_FP_MAX && output_gamma >= PNG_FP_MIN)
- png_set_alpha_mode_fixed(png_ptr, mode, (png_fixed_point)output_gamma);
- else
- png_fixed_error(png_ptr, "png_set_alpha_mode gamma");
+ png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
+ output_gamma));
}
# endif
#endif
@@ -719,6 +757,10 @@
if (png_ptr == NULL)
return;
+ /* New in libpng-1.5.3 - reserve particular negative values as flags. */
+ scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
+ file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
+
#if PNG_LIBPNG_VER >= 10600
/* Checking the gamma values for being >0 was added in 1.5.3 along with the
* premultiplied alpha support; this actually hides an undocumented feature
@@ -749,9 +791,8 @@
void PNGAPI
png_set_gamma(png_structp png_ptr, double scrn_gamma, double file_gamma)
{
- png_set_gamma_fixed(png_ptr,
- png_fixed(png_ptr, scrn_gamma, "png_set_gamma screen gamma"),
- png_fixed(png_ptr, file_gamma, "png_set_gamma file gamma"));
+ png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
+ convert_gamma_value(png_ptr, file_gamma));
}
# endif /* FLOATING_POINT_SUPPORTED */
#endif /* READ_GAMMA */
diff --git a/pngset.c b/pngset.c
index 1b0fd1d..2c58f7f 100644
--- a/pngset.c
+++ b/pngset.c
@@ -545,7 +545,7 @@
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
# ifdef PNG_gAMA_SUPPORTED
- png_set_gAMA_fixed(png_ptr, info_ptr, 45455L);
+ png_set_gAMA_fixed(png_ptr, info_ptr, PNG_GAMMA_sRGB_INVERSE);
# endif
# ifdef PNG_cHRM_SUPPORTED
