how to compress a yuv420 raw data using opj_compress in lossless

[duankong]

I coule compress a yuv444 raw data with this code in lossless

ffmpeg  -y -i image -pix_fmt yuvj444p source.yuv

cp source.yuv source.raw

opj_compress -i source.raw -o temp.jp2 -F '%s,%s,%s,%s,u@1x1:1x1:1x1' % (width, height, 3, 8) -r 1 

opj_decompress -i temp.jp2-o decoded.raw

cp decode.raw decode.yuv

but when i change the sampling mode into yuv420

ffmpeg  -y -i image -pix_fmt yuvj420p source420.yuv

cp source420.yuv source420.raw

opj_compress -i source420.raw -o temp.jp2 -F '%s,%s,%s,%s,u@1x1:2x2:2x2' % (width, height, 3, 8) -r 1 

opj_decompress -i temp.jp2-o decoded.raw

cp decode.raw decode.yuv

• I know the decoded.raw is in 444 format. I try to convert it to 420 sampling ,but it is not lossless with source420.yuv.

• I also try to expand source420.yuv to 444 format ,but it is not lossless with decoded.yuv.

• In a word:I can't get a lossless result.

Note: I caculate the psnrbetween source.yuv/souce420.yuv and decode.yuv with ffmpeg

[duankong]

I try to this code below

ffmpeg  -y -i image -pix_fmt yuvj420p source420.yuv

cp source420.yuv source420.raw

opj_compress -i source420.raw -o temp.jp2 -F '%s,%s,%s,%s,u@1x1:2x2:2x2' % (width, height, 3, 8) -r 1 

opj_decompress -i temp.jp2-o decoded.ppm

ffmpeg  -y -i decoded.ppm-pix_fmt yuvj420p decoded420.yuv

• It's different to decode into a ppm file and then to convert it to decoded420.yuv .

But in openjpeg code stream the information of image is in YUV format? I do not certain.

• It lossy to convert a YUV file to ppm file .

• Also it's lossy to convert a ppm to YUV file if not in YCoCg

So the psnr between decoded420.yuv and source420.yuv is 56.66 ,it large compare the commom psnr,may be it can be consider as lossless ? But actually ,it's not lossless. I'm not sure if the lossy cause by the convert between ppm and YUVor other problem. Or both them.