On Sat, 6 Nov 2021 at 13:01, Paul B Mahol <one...@gmail.com> wrote: > > On Thu, Nov 4, 2021 at 9:41 AM Tom Vercauteren <tom.vercaute...@m4x.org> > wrote: > > > > > 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. > > > > > You can always store it into rawvideo (without any headers) and than > interpret it as 10bit with specifying ffmpeg rawvideo demuxer parameters.
Thanks, that was very helpful. By using temporary rawvideo files, I am now able to start from a grayscale16bit png where only the 10 least significant bits are used, get a 10 bit hevc mkv file, and losslessly recover a 16 bit png. the commands I use are listed below. Is there a way to do this without the temporary rawvideo files? ``` # convert to rawvideo in 16 bits ffmpeg -y -i gradient10bit-lsb.png -f rawvideo -pix_fmt gray16le gradient10bit-lsb.raw # convert to mkv in 10 bits by tricking the rawvideo demuxer # into thinking the input is a 10 bit video ffmpeg -y -f rawvideo -pixel_format gray10le -video_size 64x64 -i gradient10bit-lsb.raw -c:v libx265 -x265-params lossless=1 -pix_fmt gray10le gradient10bit-lsb.mkv # convert to raw 10 bit ffmpeg -y -i gradient10bit-lsb.mkv -f rawvideo -pix_fmt gray10le gradient10bit-lsb-postmkv.raw # convert back to png 16bits by tricking the rawvideo demuxer # into thinking the input is 16 bits ffmpeg -y -f rawvideo -pixel_format gray16le -video_size 64x64 -i gradient10bit-lsb-postmkv.raw -pix_fmt gray16be recons-gradient10bit-lsb.png # compare magick compare -verbose -metric mae gradient10bit-lsb.png recons-gradient10bit-lsb.png diff-lsb.png ``` Best wishes, Tom _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
