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A comment on H.264 is Magic (2016). Parent comment

Re:H.264 is Magic (2016) by brigade on Thursday March 17, 2022 @04:10PM (#30715378)
Alternatively, if you're being confused by the quoted intermediate DCT precision, that's not relevant to the final output either. You cannot implement any transform, DCT especially, without having intermediate values with a greater range than the input or output. Like, even a simple average of two 8-bit values (a+b)/2 has an intermediate range of 9 bits.

The JPEG spec does specify both 8 and 12 bit sample precision for lossy, but I don't think anyone ever implemented 12-bit since libjpeg never cared about it.

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Re:H.264 is Magic (2016) by HedgeGriffon on Thursday March 17, 2022 @04:42PM (#30715664)
Libjpeg does have support for it. Unfortunately, you have to have two copies of the library, one for 8 bit and one for 12. And you have to rename all the API methods in one of the libraries so you dont get name collisions. I believe that LibTIFF has a build configuration for this so that 12bit JPEG data can be encapsulated in a TIFF file.
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