improve gainmap computation logic for dark pixels #333
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DichenZhang1
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while computing gain for near blacks or pixels with channel values zero, sdr_offset is used. This value is extremely small and can result large gainmap coefficient. During encode-decode process, if this sdr pixel flips to zero, after applying gainmap the hdr pixel will blow out. It is best if the gainmap computation logic is desensitized for dark pixels. also, conversion from wider to narrower gamut space can cause overrange values. clip only negative excursions so that domain of computeGain remains positive. Test: ./ultrahdr_app Change-Id: Id98d95d020a01db6e85e08115a4405eac07d42c1
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while computing gain for near blacks or pixels with channel values zero, sdr_offset is used. This value is extremely small and can result large gainmap coefficient. During encode-decode process, if this sdr pixel flips to zero, after applying gainmap the hdr pixel will blow out. It is best if the gainmap computation logic is desensitized for dark pixels.
also, conversion from wider to narrower gamut space can cause overrange values. clip only negative excursions so that domain of computeGain remains positive.
Test: ./ultrahdr_app