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Why there are sRGB/RGB modes in ASTC encoder

JoshuaLyn

In ASTC encoder, we can use -cl to compress RGB texture  and -cs to compress sRGB texture, but why does it need to tell sRGB/RGB texture for astc encoder. From the astc encoder code, I can see some different in processing, but I don't understant why it is needed 

(1) astc encoder tries to fit the texels to a line, it relates to the data distributition, fitting sRGB texure or RGB texture will be not different.

(2) ASTC spec CEM, there is only LDR/HDR mode, no LDR_sRGB mode , so sRGB/RGB will share the LDR CEM.

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  • 0 in reply to Peter Harris

    Thanks

    I check the doc

    (1) OpenGL ES provide GL_COMPRESSED_RGBA_ASTC/GL_COMPRESSED_SRGB8_ALPHA8_ASTC for linear and sRGB，so it is not needed in the encoded data.

    (2) ASTC is specified to decompress texels into fp16 intermediate values, except for sRGB which always decompresses into 8-bit UNORM intermediates. For many use cases this gives more dynamic range and precision than required. This can cause a reduction in both texture cache efficiency and texture filtering performance due to the larger decompressed data size.

    so my understanding is that the astcencoder provides -cs -ds -ts to make the test result more close to the hardware implematation

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  • 0 in reply to Peter Harris

    Thanks

    I check the doc

    (1) OpenGL ES provide GL_COMPRESSED_RGBA_ASTC/GL_COMPRESSED_SRGB8_ALPHA8_ASTC for linear and sRGB，so it is not needed in the encoded data.

    (2) ASTC is specified to decompress texels into fp16 intermediate values, except for sRGB which always decompresses into 8-bit UNORM intermediates. For many use cases this gives more dynamic range and precision than required. This can cause a reduction in both texture cache efficiency and texture filtering performance due to the larger decompressed data size.

    so my understanding is that the astcencoder provides -cs -ds -ts to make the test result more close to the hardware implematation

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