[Courses] [gimp] Exporting and image formats

[Carol Spears]

On Mon, Jan 31, 2005 at 09:22:22AM +1100, Mary wrote:
> 
> The exporter is fairly sensible: it will do things like turn transparent
> areas into your default background colour in formats that can't handle
> transparency; and merge all the layers into one for formats that can't
> handle layers.
> 
<snipped because i am going to talk about pngs>

>  *.png: PNG is a lossless format optimised for storing images with large
>  blocks of a single colour (as an example, imagine a flow chart or
>  diagram with lots of blue boxes or something) in a small amount of
>  space.
> 
<more snippage>
> 
>  *.gif: GIF is an older format which has roughly the same use as PNG. It
>  has better support than PNG in old web browsers, but was patented for a
>  long time and may still be in some countries. Because it was actually
>  illegal for software to produce GIF files without paying royalties,
>  there was a big push a while back for Free Software users to adopt PNG
>  instead. The PNG format is also meant to be technically superior, but I
>  don't know exactly why.
> 
png is a wonderful format because it handles so many different types of
image information presented in many different ways.  png can is a pita 
(especially for beginners) because it handles so many different types of
image information presented in different ways.

Jon's problem earlier with the image that could not be saved as a jpeg
but could be saved as a png is a good example of the png flexibility.
transparency is an images ability to have transparent areas displayed.
and i really meant ability in that last sentence because Jon's problem
with the size of the png is because he also saved the images ability to
display transparent even though there probably were no transparent
areas.

(similar, i am going to use my old armenian friends way of calling
everyone "he" when in need of a pronoun ....)

so png is technically superior.  it allows itself to be saved with this
transparent color ability (probably akkana will be explaining this in
future courses) or without it.  it allows itself to be saved in
different modes (also probably in future courses) like "indexed" or
"RGB" or "grayscale".  the ease of saving these files does nothing to
help users know things to do to make the file smaller.  it also saves
images with actual transparent areas in a simple and often ugly way like
gifs do or beautifully, as gifs cannot do.

the simple fix for Jon's problem was to <Image>->Image->Flatten Image
before saving.  i dont know if this made the png smaller than the jpeg
of the same format, i do know that the flattened png is much smaller
than the unflattened png.

btw, that akkana, he is doing a wonderful job with this course.  i am
anxious to read his next installation.

carol

different types of