One of the most common purposes GIMP is used for
is to prepare images for adding them to a web site. This means that
images should look as nice as possible while keeping the file
size as small as possible. This little step-by-step guide will tell
you how to achieve a smaller file size with minimal degradation of
image quality.
5.1.
Images with an Optimal Size/Quality Ratio
An optimal image for the web depends upon the image type and the file
format you have to use. If you want to put a photograph with a lot of
colors online, you have to use
JPEG
as your primary file format. If your image contains fewer colors, that
is, if it is not a photograph, but is more a drawing you created (such
as a button or a screenshot), you would be better off using
PNG
format. We will guide you through the process of doing this.
First, open the image as usual. I have opened our Wilber as an
example image.
Figure 6.3.
The Wilber image opened in RGBA mode.
The image is now in RGB mode, with an additional
Alpha channel
(RGBA). There is usually no need to have an alpha channel for your
web image. You can remove the alpha channel by
flattening the image.
If you open a photograph, you probably won't have to remove the
alpha channel, because a photograph doesn't usually have one, so the
file is already opened in RGB mode.
Note
If the image has a soft transition into the transparent areas, you
cannot remove the alpha channel, since the information which would
be used for fading out will not be saved in the file. If you would
like to save an image with transparent areas which do not have a
soft transition, (similar to
GIF
), you can remove the alpha channel.
After you have flattened the image, you are able to save the image in PNG format for your
web site.
Note
You can save your image in PNG format with the default settings, but
using maximum compression. Doing this will have no negative affects on
the quality of the picture, as it would have with
JPEG
format. If your image is a photograph with lots of colors, you would
be better off saving it as jpeg. The main thing is to find the best
tradeoff between quality and compression. You can find more
information about this topic in JPEG.
Published under the terms of the GNU General Public License
![[Note]](../images/note.png)
