// Returns a colorSpace object that represents any color space information in
// the encoded data. If the encoded data contains no color space, this will
// return NULL.
sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
#if (PNG_LIBPNG_VER_MAJOR > 1) || (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR >= 6)
// First check for an ICC profile
png_bytep profile;
png_uint_32 length;
// The below variables are unused, however, we need to pass them in anyway or
// png_get_iCCP() will return nothing.
// Could knowing the |name| of the profile ever be interesting? Maybe for debugging?
png_charp name;
// The |compression| is uninteresting since:
// (1) libpng has already decompressed the profile for us.
// (2) "deflate" is the only mode of decompression that libpng supports.
int compression;
if (PNG_INFO_iCCP == png_get_iCCP(png_ptr, info_ptr, &name, &compression, &profile,
&length)) {
return SkColorSpace::NewICC(profile, length);
}
// Second, check for sRGB.
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
// sRGB chunks also store a rendering intent: Absolute, Relative,
// Perceptual, and Saturation.
// FIXME (msarett): Extract this information from the sRGB chunk once
// we are able to handle this information in
// SkColorSpace.
return SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
}
// Next, check for chromaticities.
png_fixed_point XYZ[9];
float toXYZD50[9];
png_fixed_point gamma;
float gammas[3];
if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &XYZ[0], &XYZ[1], &XYZ[2], &XYZ[3], &XYZ[4],
&XYZ[5], &XYZ[6], &XYZ[7], &XYZ[8])) {
// FIXME (msarett): Here we are treating XYZ values as D50 even though the color
// temperature is unspecified. I suspect that this assumption
// is most often ok, but we could also calculate the color
// temperature (D value) and then convert the XYZ to D50. Maybe
// we should add a new constructor to SkColorSpace that accepts
// XYZ with D-Unkown?
for (int i = 0; i < 9; i++) {
toXYZD50[i] = png_fixed_point_to_float(XYZ[i]);
}
if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
float value = png_inverted_fixed_point_to_float(gamma);
gammas[0] = value;
gammas[1] = value;
gammas[2] = value;
} else {
// Default to sRGB (gamma = 2.2f) if the image has color space information,
// but does not specify gamma.
gammas[0] = 2.2f;
gammas[1] = 2.2f;
gammas[2] = 2.2f;
}
SkMatrix44 mat(SkMatrix44::kUninitialized_Constructor);
mat.set3x3ColMajorf(toXYZD50);
return SkColorSpace::NewRGB(gammas, mat);
}
// Last, check for gamma.
if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
// Guess a default value for cHRM? Or should we just give up?
// Here we use the identity matrix as a default.
// Set the gammas.
float value = png_inverted_fixed_point_to_float(gamma);
gammas[0] = value;
gammas[1] = value;
gammas[2] = value;
return SkColorSpace::NewRGB(gammas, SkMatrix44::I());
}
#endif // LIBPNG >= 1.6
// Finally, what should we do if there is no color space information in the PNG?
// The specification says that this indicates "gamma is unknown" and that the
// "color is device dependent". I'm assuming we can represent this with NULL.
// But should we guess sRGB? Most images are sRGB, even if they don't specify.
return nullptr;
}
// Returns a colorSpace object that represents any color space information in
// the encoded data. If the encoded data contains no color space, this will
// return NULL.
sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
#if (PNG_LIBPNG_VER_MAJOR > 1) || (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR >= 6)
// First check for an ICC profile
png_bytep profile;
png_uint_32 length;
// The below variables are unused, however, we need to pass them in anyway or
// png_get_iCCP() will return nothing.
// Could knowing the |name| of the profile ever be interesting? Maybe for debugging?
png_charp name;
// The |compression| is uninteresting since:
// (1) libpng has already decompressed the profile for us.
// (2) "deflate" is the only mode of decompression that libpng supports.
int compression;
if (PNG_INFO_iCCP == png_get_iCCP(png_ptr, info_ptr, &name, &compression, &profile,
&length)) {
return SkColorSpace::NewICC(profile, length);
}
// Second, check for sRGB.
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
// sRGB chunks also store a rendering intent: Absolute, Relative,
// Perceptual, and Saturation.
// FIXME (msarett): Extract this information from the sRGB chunk once
// we are able to handle this information in
// SkColorSpace.
return SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
}
// Next, check for chromaticities.
png_fixed_point toXYZFixed[9];
float toXYZ[9];
png_fixed_point whitePointFixed[2];
float whitePoint[2];
png_fixed_point gamma;
float gammas[3];
if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &toXYZFixed[0], &toXYZFixed[1], &toXYZFixed[2],
&toXYZFixed[3], &toXYZFixed[4], &toXYZFixed[5], &toXYZFixed[6],
&toXYZFixed[7], &toXYZFixed[8]) &&
png_get_cHRM_fixed(png_ptr, info_ptr, &whitePointFixed[0], &whitePointFixed[1], nullptr,
nullptr, nullptr, nullptr, nullptr, nullptr))
{
for (int i = 0; i < 9; i++) {
toXYZ[i] = png_fixed_point_to_float(toXYZFixed[i]);
}
whitePoint[0] = png_fixed_point_to_float(whitePointFixed[0]);
whitePoint[1] = png_fixed_point_to_float(whitePointFixed[1]);
SkMatrix44 toXYZD50(SkMatrix44::kUninitialized_Constructor);
if (!convert_to_D50(&toXYZD50, toXYZ, whitePoint)) {
toXYZD50.set3x3RowMajorf(gSRGB_toXYZD50);
}
if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
float value = png_inverted_fixed_point_to_float(gamma);
gammas[0] = value;
gammas[1] = value;
gammas[2] = value;
return SkColorSpace_Base::NewRGB(gammas, toXYZD50);
}
// Default to sRGB gamma if the image has color space information,
// but does not specify gamma.
return SkColorSpace::NewRGB(SkColorSpace::kSRGB_GammaNamed, toXYZD50);
}
// Last, check for gamma.
if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
// Set the gammas.
float value = png_inverted_fixed_point_to_float(gamma);
gammas[0] = value;
gammas[1] = value;
gammas[2] = value;
// Since there is no cHRM, we will guess sRGB gamut.
SkMatrix44 toXYZD50(SkMatrix44::kUninitialized_Constructor);
toXYZD50.set3x3RowMajorf(gSRGB_toXYZD50);
return SkColorSpace_Base::NewRGB(gammas, toXYZD50);
}
#endif // LIBPNG >= 1.6
// Report that there is no color space information in the PNG. SkPngCodec is currently
// implemented to guess sRGB in this case.
return nullptr;
}
