Rename function to transferFunction #482
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include/ktx.h
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| @@ -1198,7 +1198,13 @@ typedef struct ktxAstcParams { | |||
| i.e. 6x6, 8x8, 6x5 etc*/ | |||
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| ktx_uint32_t transferFunction; | |||
| /*!< Input/output transfer function for astcenc can be {linear/srgb}*/ | |||
| /*!< Input/output transfer function for astcenc that can be {linear/srgb} | |||
| ASTC supports non-linear sRGB color space conversion at both compression and decompression time. | |||
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What conversion is actually done? I thought the data was encoded as sRGB with perhaps changes to the way error is computed during the encoding process.
Actually do we even need this field? I haven't exposed the equivalent for BasisU. The underlying encoder setting m_perceptual is always set from the transferFunction field of the texture's DFD. I can't see anything useful and correct that can be done by allowing override. BasisU's m_perceptual causes the error metrics to be computed in YCbCr space rather than RGB.
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I have submitted a fix to remove the conversion bit. AFAIK it doesn't really do any conversion per se. What this means is that if your image is in sRGB color space you need to use the transferFunction = srgb for the compression to be correct. It will create an image whose type is something like COMPRESSED_SRGB8_ALPHA8_ASTC_4x4_KHR. If the image is linear you need to provide transferFunction = linear and the image created will have a format of COMPRESSED_RGB8_ALPHA8_ASTC_4x4_KHR. If a user has sRGB input image and want linear output, they first have to convert to Linear manually then pass it to the compressor with transferFunction = linear and same for Linear to sRGB, i.e. the encoder won't do conversion for them.
I just needed this flag in here so I can carry our what the transfer function in the image was to the encoder. Is there a better way to get this in the astc_encoder.cpp scope without this flag?
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For BasisU I don't expose the equivalent in ktxBasisParams. Instead in ktxCompressBasisEx I check whether the texture is sRGB or not and set the underlying basisu encoder's m_perceptual parameter to true if it is. See here.
Presumably the ASTC encoder has an equivalent parameter, something you must be setting from the value of transferFunction.
I think I just found a bug. I probably should be setting m_perceptual for uastc encoding as well.
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I have used something similar now in ca5309f I think that works.
I was actually already using the DFD way of getting this in astcEncoderAction if the image provided option failed. Now cleaned that up.
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Thanks! |
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