ImageMagick

If the original doesn't have very many colors the resized one will have more. Use "identify -verbose" to find out how many colors are in your original, your output jpeg, and your output png. That may provide an explanation for the size differences.

Identify says the alpha is 1-bit even though it's really 8-bit, when the only values are 0 and 255. The "resize" operation creates other values due to interpolation of alphas. To get back to the 0/255 condition, use -ordered-dither command (look it up to get the exact syntax; it's something like "-o...

There's a free application called "intergif" which might be useful to you as a final optimization step. I haven't used it lately but had good luck with it in the past.

Glenn

Try -quality 90
The "0" in the ones digit means not to use PNG filtering.
PNG filtering is usually ineffective when there are few (e.g. 256) colors.

Hi, I'm fiddling around with convert for a while now. So i just give it a try in this forum :) My input image can be in landscape format or in panel format. (up to 1000x1000 pixels) Now i want to create a quadratic Thumbnail out of it. With one command-line-call if possible. My output size should b...

P.S. you could try -sample instead of -resize.

Glenn

May I have a copy of your source image? There is no such thing as a 1-bit alpha PNG unless you mean a PNG where the transparency is carried in the tRNS chunk.

Glenn