There's lots of things you can do to make PNG's smaller.
 
If you save them as Indexed PNG's and reduce the colours, you may end up with smaller filesizes. Change the image mode to Indexed and it should prompt you for number of colours and other options.
 
After exporting the PNG, it still isn't very efficient... most apps like Gimp, Photoshop, Paintshop... they don't do a good job optimizing the PNG export. You may want to try PNG crushing programs that will optimize the PNG much more. Personally I use something called Megaopt: http://www.hydrogenaudio.org/forums/index.php?showtopic=16167 ... it's a DOS script that uses 5 PNG crushers and compares the results. Also, a WIndows GUI program called "PNG Gauntlet" does pretty good too (same as Megaopt almost). Search the net for that.
 
There's other tricks and things you can do... but they only save a matter of 100's of bytes.
 
Kalle
 
 
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of Jim Clark
Sent: Thursday, April 14, 2005 4:17 PM
To: gimp-user@lists.xcf.berkeley.edu
Subject: [Gimp-user] png compression

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

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