Re: QUESTION: converting to GIFs

[Emru Townsend <emru -at- CORECO -dot- COM>]

Jacqueline Fry <jfry -at- ARRAY -dot- CA> asked:



>Can anyone suggest an application that will convert JPEGs and TIFs to
GIFs?
>I used Microsofts Image Composer (beta) to save a JPEG file as a GIF so I
>could use it with Microsoft GIF Animator (beta), but the resulting GIF
image
>was less than perfect. Some of picture looked like it'd been
'highlighted',
>and some colours had been replaced with others. Very bizarre. Also, the
only
>other app I have that *could* do the job, Corel PhotoPaint, can open
>existing GIFs, but other image formats cannot be re-saved as GIFs (as far
as
>I can tell).



To paraphrase Richard Armour, brevity is the soul of wit, but what follows
is neither short nor funny.



Most graphics programs allow you to convert from one format to the other by
loading and re-saving.  However, what many of them don't do is warn you of
some of the issues involved.  Your resulting GIF probably looked "less than
perfect" because of the means used to convert from a 24-bit TIFF or JPEG to
an 8-bit GIF.  Simply put, JPEGs and TIFFs have a wider range of colors
available to them (24^2, or roughly 16.7 million) compared to GIF (2^8, or
256).  When you convert from JPEG or TIFF to GIF, the colors have to be
shoehorned from a 24-bit color space to an 8-bit color space; in short,
you're losing some color definition.



There are two ways that this is done.  One, which sounds like the one you
describe, is to replace any colors with their 8-bit equivalents.  If a
pixel is defined as a color which isn't an acceptable 8-bit color, it is
replaced with the closest one possible.  The net effect is that the
subtleties of tone usually end up being lost.  The second technique
involves dithering (some programs call it diffusion), where areas of colors
that don't map to the 8-bit color space are simulated by creating a pattern
of differently-colored dots.  For instance, if a particular shade of purple
isn't available, it would be approximated by creating a pattern of a purple
and a blue which are acceptable, which would (hopefully) fool the eye into
seeing something close to the original color.  The down side is that this
sometimes causes the picture to look grainy.



So here's where your problem lies: by saving a JPEG file as a GIF, you're
relying on the software to automatically convert from 24-bit to 8-bit,
rather than doing it yourself and having some control over the process.  I
haven't used Image Composer for more than a few minutes, so I don't know
about its specific features, but most graphics programs will let you
convert a 24-bit image to an 8-bit image before saving it, using a variety
of settings.  Some programs even give you control over the type and
intensity of the dithering, if you choose to use it.  Different images will
require different methods, so you'll need to play around with the different
methods before you get that instinctive feel as to which will be best.



Oh, and your second problem -- not being able to re-save the image as a GIF
-- is probably because Corel PhotoPaint might not allow you to save a
24-bit image in an 8-bit format, as with some other software.  In that
case, you'll have to change the format manually, and then save it as a GIF.



>Alternately, are there any GIF animation programs that will allow me to
>import a picture with a different file extension, and *then* save it as a
>GIF? It'd be nice if any of the programs mentioned could be downloaded
from
>the Internet, or are available as beta programs.



Um, I *think* Microsoft's GIF Animator (which should have been included
with your beta of Image Composer) and Ulead's GIF Composer (or whatever
it's called) do, but don't quote me on that.



Emru Townsend

emru -at- coreco -dot- com

Montreal, Quebec

	http://www.documentation.com/, or http://www.dejanews.com/