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Re: re-sizing png's

  • Subject: Re: re-sizing png's
  • From: Mark Tranchant <mark@tranchant.plus.com>
  • Date: Fri, 14 Jan 2005 08:12:51 +0000
  • In-reply-to: <34oheoF4drvofU1@individual.net>
  • Newsgroups: comp.graphics.apps.gimp
  • Organization: Customer of PlusNet plc (http://www.plus.net)
  • References: <34oheoF4drvofU1@individual.net>
  • User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)
  • Xref: news.mcc.ac.uk comp.graphics.apps.gimp:12661
sam ende wrote:
how do you re-size png's to a smaller file size best in gimp, (i don't
understand the window that comes up; it's differnt to the jpeg window
resize window) --there is a slider for compression and other options
but i don't know what they mean

The compression level is a balance of CPU time to file size. The format is lossless whatever ratio you select, so the image will not be altered at all. The level just tells teh encoder how hard to try to reduce the file size.

If you are using alpha transparency, you should be aware that IE doesn't fully support that by default, and will use the saved background colour as the background. If ticked, this is saved as the currently selected background colour in the GIMP. If not ticked, I think it is black.

Gamma is theoretically a good thing to save, as your pictures will display correctly of different platforms - unfortunately, support for this is not universal.

The other options aren't really worth thinking about for your application.

If you're worried about file size, you should look at pngcrush, a command-line utility that can find the absolute smallest size your PNG can be reduced to.

and i've remade my site with new
pictures but didn't think of image size upon rendering and, obviously,
i don't really want to re-render or re-save as jpeg (as i would have to
change the html then)

Multi-file search and replace is a feature of several freeware applications, and shouldn't take a minute. "Photographic" images should be saved as JPEG, with PNG reserved for "graphics" or line art.


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