[Gimp-user] png compression

[Jim Clark]

Hmmmm...

I have a couple of pngs that I have scaled to make smaller but still visible thumbnails. Image 1 (install1.png) was 799 X 598, I scaled it to 300 X 225. install10.png was 765 X 538, scaled to 450 X 317.

Here's an ls:

10725 Apr 14 13:54 install10.png
24020 Apr 14 15:01 install10_tn.png

35217 Apr 14 13:54 install1.png
32378 Apr 14 15:01 install1_tn.png

install1.png was reduced significantly and yet the file size reduction is less than 10% (hardly worth the bother to make a smaller version) and install10.png, reduced in size by a much smaller proportion, was reduced a useful (and much greater) amount.

These were png screenshots sent to me from a Win box...I cropped them to the useful area and saved them as pngs using the default settings. Then for the thumbnails I just scaled the image and saved again.

Is there something I should be doing to get a smaller file size? I have only recently started using pngs as my users are all MS/IE folks and have not really thought about file compression much. But this seems weird to me.

I realize what I don't know about file compression (or pngs, or GIMP, or most other things discussed on this list) could fill a few books, but same source same process same tools yielded very different results. Why?

Thanks-

Jim Clark