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PNG decoder: handle gAMA chunk

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Apply gamma correction to the decoded RGB values.

This handles corner cases where the PNG file doesn't have
a standard 1/2.2 gamma value.

BUG=webp:369

Change-Id: I9907b6e2c458002de7c26d0b9e416278cca33990
This commit is contained in:
Pascal Massimino 2018-01-05 04:34:50 -08:00
parent 664c21dd01
commit 78318b30e5
1 changed files with 10 additions and 1 deletions
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11
imageio/pngdec.c
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@ -185,7 +185,6 @@ static int ExtractMetadataFromPNG(png_structp png,
}
}
}
return 1;
}
@ -265,6 +264,16 @@ int ReadPNG(const uint8_t* const data, size_t data_size,
has_alpha = !!(color_type & PNG_COLOR_MASK_ALPHA);
}
// Apply gamma correction if needed.
{
double image_gamma = 1 / 2.2, screen_gamma = 2.2;
int srgb_intent;
if (png_get_sRGB(png, info, &srgb_intent) ||
png_get_gAMA(png, info, &image_gamma)) {
png_set_gamma(png, screen_gamma, image_gamma);
}
}
if (!keep_alpha) {
png_set_strip_alpha(png);
has_alpha = 0;