Fix lossless decoding of point transformed and interleaved multi component scans - #25
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Fix lossless decoding of point transformed and interleaved multi component scans#25daker wants to merge 1 commit into
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@rii-mango hi, can you look at the proposed fix ? |
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…onent scans ScanHeader parses Al out of the SOS header and nothing ever read it, so scans encoded with a point transform decoded wrong in two ways. T.81 H.1.2.1 seeds the prediction for the first sample of a scan with 2^(P - Pt - 1), not 2^(P - 1). Lossless prediction chains additively, so a wrong seed offsets every sample in the frame: a 16 bit scan with Al = 2 came out 24576 high. The encoder also right shifted every sample by Al before encoding (T.81 A.4.1), so the decoder has to shift them back. Without it the frame keeps 1/2^Al of its dynamic range. The shift runs once the whole frame is decoded rather than in setValue, because prediction reads previously decoded samples back out of outputData and those reads have to stay in the point transformed domain. Fixes cornerstonejs/cornerstone3D#757 Fixes cornerstonejs/cornerstone3D#1116
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ScanHeader parses Al out of the SOS header and nothing ever read it, so scans encoded with a point transform decoded wrong in two ways.
T.81 H.1.2.1 seeds the prediction for the first sample of a scan with 2^(P - Pt - 1), not 2^(P - 1). Lossless prediction chains additively, so a wrong seed offsets every sample in the frame: a 16 bit scan with Al = 2 came out 24576 high.
The encoder also right shifted every sample by Al before encoding (T.81 A.4.1), so the decoder has to shift them back. Without it the frame keeps 1/2^Al of its dynamic range.
The shift runs once the whole frame is decoded rather than in setValue, because prediction reads previously decoded samples back out of outputData and those reads have to stay in the point transformed domain.
Fixes cornerstonejs/cornerstone3D#757
Fixes cornerstonejs/cornerstone3D#1116