unit test for gray ICC profiles and bugfixes

1 files changed, 34 insertions, 31 deletions

diff --git a/lodepng.h b/lodepng.h
index 8886619..788c8e6 100644
--- a/lodepng.h
+++ b/lodepng.h
@@ -89,10 +89,10 @@ source files with custom allocators.*/
 #ifdef LODEPNG_COMPILE_PNG
 /*The PNG color types (also used for raw).*/
 typedef enum LodePNGColorType {
-  LCT_GREY = 0, /*greyscale: 1,2,4,8,16 bit*/
+  LCT_GREY = 0, /*grayscale: 1,2,4,8,16 bit*/
   LCT_RGB = 2, /*RGB: 8,16 bit*/
   LCT_PALETTE = 3, /*palette: 1,2,4,8 bit*/
-  LCT_GREY_ALPHA = 4, /*greyscale with alpha: 8,16 bit*/
+  LCT_GREY_ALPHA = 4, /*grayscale with alpha: 8,16 bit*/
   LCT_RGBA = 6 /*RGB with alpha: 8,16 bit*/
 } LodePNGColorType;
 
@@ -337,7 +337,7 @@ typedef struct LodePNGColorMode {
   transparent color key (tRNS)
 
   This color uses the same bit depth as the bitdepth value in this struct, which can be 1-bit to 16-bit.
-  For greyscale PNGs, r, g and b will all 3 be set to the same.
+  For grayscale PNGs, r, g and b will all 3 be set to the same.
 
   When decoding, by default you can ignore this information, since LodePNG sets
   pixels with this key to transparent already in the raw RGBA output.
@@ -345,7 +345,7 @@ typedef struct LodePNGColorMode {
   The color key is only supported for color types 0 and 2.
   */
   unsigned key_defined; /*is a transparent color key given? 0 = false, 1 = true*/
-  unsigned key_r;       /*red/greyscale component of color key*/
+  unsigned key_r;       /*red/grayscale component of color key*/
   unsigned key_g;       /*green component of color key*/
   unsigned key_b;       /*blue component of color key*/
 } LodePNGColorMode;
@@ -368,7 +368,7 @@ unsigned lodepng_get_bpp(const LodePNGColorMode* info);
 /*get the amount of color channels used, based on colortype in the struct.
 If a palette is used, it counts as 1 channel.*/
 unsigned lodepng_get_channels(const LodePNGColorMode* info);
-/*is it a greyscale type? (only colortype 0 or 4)*/
+/*is it a grayscale type? (only colortype 0 or 4)*/
 unsigned lodepng_is_greyscale_type(const LodePNGColorMode* info);
 /*has it got an alpha channel? (only colortype 2 or 6)*/
 unsigned lodepng_is_alpha_type(const LodePNGColorMode* info);
@@ -415,7 +415,7 @@ typedef struct LodePNGInfo {
   This uses the same color mode and bit depth as the PNG (except no alpha channel),
   with values truncated to the bit depth in the unsigned integer.
 
-  For greyscale and palette PNGs, the value is stored in background_r. The values
+  For grayscale and palette PNGs, the value is stored in background_r. The values
   in background_g and background_b are then unused.
 
   So when decoding, you may get these in a different color mode than the one you requested
@@ -425,15 +425,15 @@ typedef struct LodePNGInfo {
   these values. The encoder normally ignores info_png.color when auto_convert is on, but will
   use it to interpret these values (and convert copies of them to its chosen color model).
 
-  When encoding, avoid setting this to an expensive color, such as a non-grey value
-  when the image is grey, or the compression will be worse since it will be forced to
+  When encoding, avoid setting this to an expensive color, such as a non-gray value
+  when the image is gray, or the compression will be worse since it will be forced to
   write the PNG with a more expensive color mode (when auto_convert is on).
 
   The decoder does not use this background color to edit the color of pixels. This is a
   completely optional metadata feature.
   */
   unsigned background_defined; /*is a suggested background color given?*/
-  unsigned background_r;       /*red/grey/palette component of suggested background color*/
+  unsigned background_r;       /*red/gray/palette component of suggested background color*/
   unsigned background_g;       /*green component of suggested background color*/
   unsigned background_b;       /*blue component of suggested background color*/
 
@@ -523,12 +523,12 @@ typedef struct LodePNGInfo {
   profile as closely as possible, if you wish to do this you should provide the correct values for gAMA and cHRM and
   enable their '_defined' flags since LodePNG will not automatically compute them from the ICC profile.
 
-  For encoding, the ICC profile is required by the PNG specification to be an "RGB" profile for non-grey
-  PNG color types and a "GRAY" profile for grey PNG color types. If you disable auto_convert, you must ensure
+  For encoding, the ICC profile is required by the PNG specification to be an "RGB" profile for non-gray
+  PNG color types and a "GRAY" profile for gray PNG color types. If you disable auto_convert, you must ensure
   the ICC profile type matches your requested color type, else the encoder gives an error. If auto_convert is
   enabled (the default), and the ICC profile is not a good match for the pixel data, this will result in an encoder
-  error if the pixel data has non-grey pixels for a GRAY profile, or a silent less-optimal compression of the pixel
-  data if the pixels could be encoded as greyscale but the ICC profile is RGB.
+  error if the pixel data has non-gray pixels for a GRAY profile, or a silent less-optimal compression of the pixel
+  data if the pixels could be encoded as grayscale but the ICC profile is RGB.
 
   To avoid this do not set an ICC profile in the image unless there is a good reason for it, and when doing so
   make sure you compute it carefully to avoid the above problems.
@@ -656,7 +656,7 @@ Used internally by default if "auto_convert" is enabled. Public because it's use
 NOTE: This is not related to the ICC color profile, search "iccp_profile" instead to find the ICC/chromacity/...
 fields in this header file.*/
 typedef struct LodePNGColorProfile {
-  unsigned colored; /*not greyscale*/
+  unsigned colored; /*not grayscale*/
   unsigned key; /*image is not opaque and color key is possible instead of full alpha*/
   unsigned short key_r; /*key values, always as 16-bit, in 8-bit case the byte is duplicated, e.g. 65535 means 255*/
   unsigned short key_g;
@@ -664,7 +664,7 @@ typedef struct LodePNGColorProfile {
   unsigned alpha; /*image is not opaque and alpha channel or alpha palette required*/
   unsigned numcolors; /*amount of colors, up to 257. Not valid if bits == 16.*/
   unsigned char palette[1024]; /*Remembers up to the first 256 RGBA colors, in no particular order*/
-  unsigned bits; /*bits per channel (not for palette). 1,2 or 4 for greyscale only. 16 if 16-bit per channel required.*/
+  unsigned bits; /*bits per channel (not for palette). 1,2 or 4 for grayscale only. 16 if 16-bit per channel required.*/
   size_t numpixels;
 } LodePNGColorProfile;
 
@@ -677,7 +677,7 @@ unsigned lodepng_get_color_profile(LodePNGColorProfile* profile,
                                    const unsigned char* image, unsigned w, unsigned h,
                                    const LodePNGColorMode* mode_in);
 /*The function LodePNG uses internally to decide the PNG color with auto_convert.
-Chooses an optimal color model, e.g. grey if only grey pixels, palette if < 256 colors, ...*/
+Chooses an optimal color model, e.g. gray if only gray pixels, palette if < 256 colors, ...*/
 unsigned lodepng_auto_choose_color(LodePNGColorMode* mode_out,
                                    const unsigned char* image, unsigned w, unsigned h,
                                    const LodePNGColorMode* mode_in);
@@ -1241,7 +1241,7 @@ LodePNGColorMode info_raw
 When decoding, here you can specify which color type you want
 the resulting raw image to be. If this is different from the colortype of the
 PNG, then the decoder will automatically convert the result. This conversion
-always works, except if you want it to convert a color PNG to greyscale or to
+always works, except if you want it to convert a color PNG to grayscale or to
 a palette with missing colors.
 
 By default, 32-bit color is used for the result.
@@ -1337,7 +1337,7 @@ can encode the colors of all pixels without information loss.
 An important thing to note about LodePNG, is that the color type of the PNG, and
 the color type of the raw image, are completely independent. By default, when
 you decode a PNG, you get the result as a raw image in the color type you want,
-no matter whether the PNG was encoded with a palette, greyscale or RGBA color.
+no matter whether the PNG was encoded with a palette, grayscale or RGBA color.
 And if you encode an image, by default LodePNG will automatically choose the PNG
 color type that gives good compression based on the values of colors and amount
 of colors in the image. It can be configured to let you control it instead as
@@ -1345,10 +1345,10 @@ well, though.
 
 To be able to do this, LodePNG does conversions from one color mode to another.
 It can convert from almost any color type to any other color type, except the
-following conversions: RGB to greyscale is not supported, and converting to a
+following conversions: RGB to grayscale is not supported, and converting to a
 palette when the palette doesn't have a required color is not supported. This is
 not supported on purpose: this is information loss which requires a color
-reduction algorithm that is beyong the scope of a PNG encoder (yes, RGB to grey
+reduction algorithm that is beyong the scope of a PNG encoder (yes, RGB to gray
 is easy, but there are multiple ways if you want to give some channels more
 weight).
 
@@ -1369,10 +1369,10 @@ decoding to have another color type, a conversion is done by LodePNG.
 
 The PNG specification gives the following color types:
 
-0: greyscale, bit depths 1, 2, 4, 8, 16
+0: grayscale, bit depths 1, 2, 4, 8, 16
 2: RGB, bit depths 8 and 16
 3: palette, bit depths 1, 2, 4 and 8
-4: greyscale with alpha, bit depths 8 and 16
+4: grayscale with alpha, bit depths 8 and 16
 6: RGBA, bit depths 8 and 16
 
 Bit depth is the amount of bits per pixel per color channel. So the total amount
@@ -1421,15 +1421,22 @@ To avoid some confusion:
  the raw image correctly before encoding.
 -both encoder and decoder use the same color converter.
 
+The function lodepng_convert does the color conversion. It is available in the
+interface but normally isn't needed since the encoder and decoder already call
+it.
+
 Non supported color conversions:
--color to greyscale: no error is thrown, but the result will look ugly because
-only the red channel is taken
--anything to palette when that palette does not have that color in it: in this
-case an error is thrown
+-color to grayscale when non-gray pixels are present: no error is thrown, but
+the result will look ugly because only the red channel is taken (it assumes all
+three channels are the same in this case so ignores green and blue). The reason
+no error is given is to allow converting from three-channel grayscale images to
+one-channel even if there are numerical imprecisions.
+-anything to palette when the palette does not have an exact match for a from-color
+in it: in this case an error is thrown
 
 Supported color conversions:
 -anything to 8-bit RGB, 8-bit RGBA, 16-bit RGB, 16-bit RGBA
--any grey or grey+alpha, to grey or grey+alpha
+-any gray or gray+alpha, to gray or gray+alpha
 -anything to a palette, as long as the palette has the requested colors in it
 -removing alpha channel
 -higher to smaller bitdepth, and vice versa
@@ -1442,10 +1449,6 @@ false.
 as the PNG has, by setting the color_convert setting to false. Settings in
 info_raw are then ignored.
 
-The function lodepng_convert does the color conversion. It is available in the
-interface but normally isn't needed since the encoder and decoder already call
-it.
-
 6.3. padding bits
 -----------------