> > Apologies for cross-posting a question I initially posted on stackoverflow > > ( > > https://stackoverflow.com/q/69739665/17261462) but having had no response > > there I thought this mailing list may be a better place for it. > > > > I am trying to encode 10 bit images losslessly in a video format. The > > images are stored as 16 bit png files (but only use 10 bit - currently the > > least significant ones) and I have been working with ffmpeg to create and > > read back the video files. > > > > My best attempt so far is based on > > https://stackoverflow.com/a/66180140/17261462 but as mentioned there, I > > get > > some pixel intensity differences which may be due to rounding when > > converting between 10 and 16 bit representation. I tried a few different > > means (bit shifting, left bit replication, floating point based scaling) > > but haven't yet figured out how to get a trully lossless reconstruction. > > > > Below is a small piece of python code to replicate my issue. I probably am > > doing something wrong there so feedback would be appreciated. > > > > > Upload input png somewhere? > > I guess that png files use only first 10bits from least significant bit.
Thanks Paul. The python snippet I provided was creating the png on the flies but for convenience I am attaching here an example 16bit png that uses all least significant 10bits. I also provide alternative versions using either the 10 most significant bits, rescaling the intensities with ROUND(input * MAXOUTSAMPLE / MAXINSAMPLE or using left bit replication (http://www.libpng.org/pub/png/spec/1.1/PNG-Encoders.html). For eae of use, here are also the ffmpeg commands in plain text and an comparison with imagemagick so as to avoid the need for python. Encoding: ffmpeg -y -i gradient10bit-scaledto16bits.png -c:v libx265 -x265-params lossless=1 -pix_fmt gray10be gradient10bit-scaledto16bits.mkv Decoding back to png: ffmpeg -y -i gradient10bit-scaledto16bits.mkv -pix_fmt gray16be recons-gradient10bit-scaledto16bits.png Comparison: magick compare -verbose -metric mae gradient10bit-scaledto16bits.png recons-gradient10bit-scaledto16bits.png diff-scaledto16bits.png Best wishes, Tom
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