Hi, I've got a large selection of JPEG images that I wish to reduce the size (in KB) of without losing too much quality.

I have messed about with KolourPaint, and have discovered that a 150x115 jpeg image weighing in at 28.4KB can be saved again as a JPEG, selecting 90% image quality, and is reduced to a 10KB image. The loss in image quaility is barely perceptable.

I want to do this for a large number of images, i.e. batch convert. I have tried using Imagemagik convert, but for some bizarre reason it makes the final image bigger?! (30KB).

Is there any way I can get convert to give the the results that Kolourpaint is giving me?

It's been a while but the last time I used convert, it was something like this...

for i in *jpg; do echo "$i" ; convert -size 20% "$i" -resize 20% "$i" ; done

or using -geometry may look like this...
for i in *jpg; do echo "$i" ; convert -geometry x70 "$i" -geometry x70 "$i" ; done

What about the filesize issue. Is convert using a different codec to Kolourpaint? Can I get it to use another codec?

To answer my own question.

Actual batch converting is done as above, but the quality issue I was expieriencing was occurring becasue KolourPaint was using libjpeg and imagemagick was not.

I still need to use libjpeg somehow in a batch and happily I was able to. Libjpeg also install, or at least it should install, a little program called cjpeg. So now I run.

for i in *jpg;
do echo "$i" ; convert -size 20% "$i" -resize 20% out.bmp;
cjpeg out.bmp > "$i";
done

Which should work. Basically, I use convert to turn the image into a bitmap so cjpeg can understand it, then use cjpeg to compress the image down to a smaller size.

Hope this helps someone else out there.

there's no way to do it using gimp? it would be very nice to be able to do it this way... can anyone help?

this is supposed to work from gimp 2.2 and up. i only have 2.0 and wonder if i do bother to download a newer version... so if you try and really like it - convince me!

regards
ungua

Try using Konqueror!
Tools=>Create Image Gallery. Resizes and creates thumbnails. It's a lot quicker than playing around with command line stuff.