Optimizing images

[drantin]

Don't forget that besides just 8-bit and 24-bit PNGs and GIFs, you can
also index them, reducing the color palette to just the colors used in
the image. While you probably wouldn't bother doing this on high-color
images as the reduction would be minimal to nil; on simple logos and
other low-color images, you can trim off more than 75% of the file
size without a reduction in quality as all colors from the original
image are still there.

The only caveat is remembering to set them back to RGB mode when you
want to add something to the logo that uses colors not currently in
the image, and possibly indexing again after modifying it if there
would still be a significant reduction in file size.

[Susie Sahim]

Thanks for the suggestion, Drantin.
Actually the video portion of my tutorial explains that with Adobe's
Save for Web, you can reduce file size by changing the number of
colors in the index palette.

I'm not sure I see the benefit in taking an RGB graphic, converting it
to index, and then back to RGB. If the graphic is low in colors, it is
best for it to be converted to index and saved in GIF or 8-bit PNG.
Adobe save for web does this step automatically. If it has a lot of
colors like a photo or a painting, converting it from RGB to index is
only going to make the graphic look really bad. This is why I
suggested using JPG. The file size will be smaller and it will support
the millions of colors needed to render the image beautifully.

Thanks for the interest.
-Susie

[Johannes Manhave]

On Thu, Jun 25, 2009 at 12:14 PM, Susie Sahim<bogu...@gmail.com> wrote:
>
> Thanks for the suggestion, Drantin.
> Actually the video portion of my tutorial explains that with Adobe's
> Save for Web, you can reduce file size by changing the number of
> colors in the index palette.
>
> I'm not sure I see the benefit in taking an RGB graphic, converting it
> to index, and then back to RGB. If the graphic is low in colors, it is
> best for it to be converted to index and saved in GIF or 8-bit PNG.

If the Index doesn't include the color of whatever you want to put in,
you will have to first convert to another colorspace.
Also, many graphical filters only operate on the RGB colorspace.

> Adobe save for web does this step automatically. If it has a lot of
> colors like a photo or a painting, converting it from RGB to index is
> only going to make the graphic look really bad.

If all the colors from the original image are in the index, there will
be no degradation in quality, but the gain would likely be far too
small to be noticeable.

> This is why I
> suggested using JPG. The file size will be smaller and it will support
> the millions of colors needed to render the image beautifully.
>
> Thanks for the interest.
> -Susie

Thanks for the response,
- Johannes