Re: JPG's poor quality
On Fri, Jun 06, 2003 at 04:11:42PM -0500, Charles Logan wrote:
> I'm not sure when this little problem began, but the only system changes have
> been updates from security.debian. The system is an all stable Woody box.
> The problem is that images saved in the jpg format appear horribly blurred and
> smudged. This is true no matter which application saves the image. Gimp,
> Kpaint, Xv, etc all exhibit the same behavior. If an image is saved in any
> other format, gif, png, bmp, xbm, etc, when displayed, it looks fine. The
> problem is most noticeable if text is used, but any object placed on a canvas
> with any drawing program will have a smudgy, ghost like shadow 20-40 pixels
> around the object, as well as washed out and blotchy looking color in the
> object itself. I made a simple black text on white back ground image with
> Gimp and saved it in jpg, gif, and tif formats. gif and tif look nice and
> crisp and clean when the image is viewed with a web browser or a image
> viewing program, but the jpg version looks terrible. Other jpg images from
> other sources appear fine, so it has to be something happening when a program
> on this system saves a jpg image. My default desktop is KDE 2.2.2, with X11
> 4.2.0. I have also tried other window managers, Gnome, Fvwm, IceWm but the
> same results occur no matter what. All other graphics related items seem to
> be fine. The default desktop is 800x600 with 24 bit depth, although I have
> also tried lower resolutions and color depth with no change. The video card
> is a Trident CyberBlade AGP. I'm quite sure that this problem is something
> fairly new as I have used Gimp previously to create many web images that were
> saved in jpg format without this happening. Any ideas as to what might be
> causing this? Thanks!
Hmm, the symptoms sound to me like artifacts of the JPEG compression
itself. You didn't mention trying different JPEG quality settings, so
I'd try that first. What settings did you use in the JPEG save dialog
box in gimp? You should see one if you try and resave a non JPEG image
into jpeg (eg save myfile.tiff as myfile.jpg). Also, what happens if
you use imagemagick to convert, like so:
convert -quality 100 myfile.tiff myfile.jpg
The other thing is that since jpeg compression is lossy, repeated saves
of the same file will cause it to lose quality. Where possible, try to
edit the file in a lossless format (like tiff or xcf) and then convert
to JPEG at the end of the cycle. And keep a non lossy version around in
case you need to edit it again later.
- Chris
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