Fix EXR encoder to write scaled values - #3195
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The EXR decoder maps file values to scaled values, but the encoder read native values. Pixel formats whose native range is not [0, 1], such as HalfVector4, wrote wrong color and alpha values to the file.
JimBobSquarePants
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formats:exr
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Description
Related to #3194
The EXR decoder and encoder did not agree. The decoder writes scaled values into the pixel format with
FromAssociatedScaledVector4. The encoder read native values withToAssociatedVector4().For a pixel format whose native range is
[0, 1], both values are equal, so the output was correct. For a pixel format with a different native range, the encoder wrote wrong values. For example,HalfVector4maps the scaled range[0, 1]to the native range[-65504, 65504]. A scaled red value of0.25went to the file as-32752, and an opaque alpha went to the file as65504.The encoder now reads
ToAssociatedScaledVector4()in the floating-point path and in the unsigned integer path.Rgba128.FromVector4in the unsigned integer path also expects components in[0, 1].I added a test that saves an
Image<HalfVector4>asHalf,Float, andUnsignedInt, loads the result asRgbaVector, and compares the scaled values. The test uses an alpha of0.5, so the clamp in the decoder cannot hide a wrong alpha value.This change does not add HDR support. Values outside
[0, 1]still clamp in 4.x. I track that work in #3194 for v5.