Differences in nconvert&xnview jpeg compression

[Andys]

Just the other day I compared jpegs that were generated with xnview and nconvert. Whatever I tried, I could not reach xnview's quality with nconvert. XNview's jpeg was always a bit sharper and cleaner that nconvert's one.
Maybe someone can tell me what's the differences are? Judging by common sense, they should have the same libs/functions for jpeg conversion.

[xnview]

Really strange, because xnview & nconvert use the same library
Are you sure that you have the same 'jpeg quality'?

[Andys]

After a few experiments with xnview (not nconvert as previously) I can say that it's because of "subsampling factor".
My mistake, I didn't try it on a lot of different pictures. All of my source images had a lot of small detailed objects (leaves).
I guess that's what the subsample setting is for, so I should rephrase the question - "Is there such a setting in nconvert?"

[xnview]

You have changed subsampling factor in XnView? Currently no setting for nconvert

[DOS386]

You have changed subsampling factor in XnView? Currently no setting for nconvert

There seems to be space for improvements



XN offers following settings:

- quality
- DCT method
- smoothing
- subsampling
- optimized Huffman (why not always on ???)
- progressive
- estimated quality (guess based on input file ???)
- rebuild
- 4 metadata keep's

NC offers:

Code: Select all

-q value          : JPEG/PNG/FPX/WIC/PDF quality (default : 100)

This is apparently wrong - PNG is lossless

Code: Select all

-i                : Interlaced GIF / Progressive JPEG
-clean value  : JPEG Clean Metadata (EXIF/IPTC/...)

so:

- quality
- metadata control
- progressive

and following settings are lacking:

- DCT method
- optimize Huffman
- subsampling