From: Chris Beaumont (cbeaumon@msri.org)
Date: Tue Nov 19 2002 - 14:12:25 PST
Both Fireworks and ImageReady offer a great feature (which originally
was only available on DeBabelizer) where you can show the palette for a
given GIF and sort the palette by various criteria, 'lock' individual
colors, and delete redundant ones. The rationale for this is that one
can trim file size in GIF files substantially by reducing the number of
colors in the color table. If you do this, you will want to 'lock' the
colors that are used in the largest areas of solid color in the
image..You will probably also want to turn off dithering, which will
always substantially increase the size of a GIF.
Tweaking an image (or a page with sliced images) is an art and listing
all of the tricks which one might use in one page is impossible.. But
some rules of thumb are easy to spell out.
Of course, use GIF for computer-generated images with large areas of
the same color, JPEG for photographs and other images with continuous
tones.
With GIFs, try to use the minimum number of colors possible to give you
the look you want. use the side by side and 4-up comparison previews in
Photoshop, Fireworks, etc. to evaluate the tradeoffs, comparing
different compression settings against the original and each other..
With critical GIFs, try introducing blurring in the horizontal plane,
and then posterizing the image (Photoshop can do this automatically
with it's lossy setting) This can dramatically reduce the size of a GIF
because of the way GIF compression works.. This is also a good way to
artistically compress photos to a tiny size.. (on some photos it works,
others it doesn't..YMMV) This is the one situation where you may want
to use GIF instead of JPEG compression for photos.. (Try it out, the
results can be startling.)
Similarly, blurring any unimportant areas of a JPEG can substantially
improve its compressibility and your ability to use high detail in the
important areas and still meet a target file size, all other things
being equal..
If you are slicing a GIF image, try to start with the same base color
table for all of the GIFs, selectively removing the unused colors from
the ones that don't need them.. Use exact and not adaptive palette.
Otherwise, you might see visible seams where the images meet.
At Berkeley this might be overkill.. On heavily-trafficked sites where
bandwidth use is metered and a few graphics are used over and over, it
can make a huge difference though..
Oh, and of course, remember to reuse the same graphics throughout a
site, to make the best possible use of caching..
Chris
On Tuesday, November 19, 2002, at 01:10 PM, Rusty Wright wrote:
> Since you're using Fireworks and it's designed for doing web graphics
> I'd suggest exploring its abilities to make the graphics smaller. Try
> different quality and compression levels. Try using gif instead of
> jpeg (or vice versa) to see if it's smaller and looks ok. When making
> gifs pay attention to the number of colors used and needed; for
> example, try lowering the number of colors to 128 or 64 and see if it
> still looks serviceable.
>
> I've never used Fireworks so I don't know if you can do all of these
> things with it but I know you can very easily do this stuff in
> Photoshop with its Export For Web.
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