[Courses] [gimp] Lesson 1: (homework done)

[Akkana Peck]

It's so much fun seeing everybody's images!  It occurred to me that
I'm not being quite fair -- I should share homework too.  I'll give
samples starting with the next lesson.  In the meantime, I put up
an image from a hike a few months ago:
Original: http://shallowsky.com/images/percwoodduck/pb161742-orig.jpg
Cropped+resized: http://shallowsky.com/images/percwoodduck/pb161742.jpg

Kjersti Bjørnestad Berg writes:
> When I saved the cropped&scaled image, I was asked what quality I
> wanted. (Default was 85.) How does this value affect the final image? It
> didn't seem to me to make much of a difference, but maybe I don't know
> what to look for?

The jpeg format uses a compression which tries to get rid of parts
of the image most people won't notice anyway.  As you compress the
image smaller and smaller, the changes gradually get more noticable.

GIMP's current default of 85 is a good compromise for making the
images reasonably small to download, while still looking quite good
to almost everyone.  I usually leave the setting the way it is when
I'm saving images for my photo pages.  But sometimes I use more
compression: if I'm making an icon for a web page that I think a
lot of people will visit, I might try to make it really small,
or if I'm making a screenshot or some other large image that
doesn't have to look good, just has to get a basic idea across.

If you have time, it's fun to take an image and use "Save As" to
save as jpg with lots of different compression settings, then view
all those images and see how they differ.  You can also google for
"jpeg quality" and find some pages with example images.

Jon Drews writes:
> and found that I could not save the image
> to *.jpg. It said:
> 
>  "Your image should be exported before it can be saved for the
> following reasons:
>                JPEG can't handle transparency"
[ ... ]
>  Also I saved the same image as a *.png but the *.png is much larger

Mary already posted a very complete answer, so I won't try to
add any more, except that if you're curious about image formats
in general, I wrote up a little primer a while ago about some
of the image formats and what they're good for.  A lot of the
info is similar to Mary's posting, but in any case it's:
http://shallowsky.com/linux/imageformats.html

Bottom line: I use png for originals, like scans, jpg for photos
on the web, and xcf (gimp's native format) for images to which I've
added extra information, like layers or text.

> What is the purpose of resizing or are you going to cover that later?

It becomes a lot more useful when you use layers, which I'll talk
about soon.  I actually don't personally use the crop tool to resize
even with layers; I use Image->Canvas Size.  But I'll describe that
in a later lesson.

	...Akkana