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jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Thu Nov 17, 2011 6:14 pm
by dubiousdawg
In cetain cases, the "-out jpeg" option seems to override the quality option.
When converting png -> jpeg or tiff -> jpeg with "-out jpeg" and "-q 100", nconvert will produce a low quality image with clear jpeg artifacts.
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Fri Nov 18, 2011 8:43 am
by xnview
Could you send comand line & sample to reproduce?
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Fri Nov 18, 2011 4:17 pm
by dubiousdawg
pierre,
thx for the response. after looking into it a bit further, it seems like it was still converting it into a .png without the -out jpeg flag, even though i specified the jpeg extension
however, there are still issues with the jpeg step. they are rather drastic for this particular image. see below"
original image (png)
Code: Select all
nconvert -out jpeg -q 90 -o crop_nconvert.jpg crop.png
Code: Select all
nconvert -out jpeg -q 100 -o crop_nconvert1.jpg crop.png
And here are the two examples that convert produces at 90 and 100 quality
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Mon Nov 21, 2011 10:31 am
by xnview
It seems that convert use subsampling 1x1,1x1,1x1 and not 2x1,1x1,1x1 as default
You can change it by using
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Mon Nov 21, 2011 2:38 pm
by dubiousdawg
Thanks for the response, Pierre! It was indeed the subsampling.
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Tue Nov 22, 2011 4:07 pm
by dubiousdawg
Pierre, is there a way to turn subsampling off completely?
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Posted: Wed Nov 23, 2011 9:10 am
by xnview
dubiousdawg wrote:Pierre, is there a way to turn subsampling off completely?
no