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.
jpeg quality bug (png -> jpeg, tiff -> jpeg)
Moderators: XnTriq, helmut, xnview
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- Posts: 4
- Joined: Thu Nov 17, 2011 6:05 pm
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Could you send comand line & sample to reproduce?
Pierre.
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- Posts: 4
- Joined: Thu Nov 17, 2011 6:05 pm
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
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)
And here are the two examples that convert produces at 90 and 100 quality
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)
It seems that convert use subsampling 1x1,1x1,1x1 and not 2x1,1x1,1x1 as default
You can change it by using
You can change it by using
Code: Select all
-subsampling 2
Pierre.
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- Posts: 4
- Joined: Thu Nov 17, 2011 6:05 pm
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Thanks for the response, Pierre! It was indeed the subsampling.
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- Posts: 4
- Joined: Thu Nov 17, 2011 6:05 pm
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
Pierre, is there a way to turn subsampling off completely?
Re: jpeg quality bug (png -> jpeg, tiff -> jpeg)
nodubiousdawg wrote:Pierre, is there a way to turn subsampling off completely?
Pierre.