TechWhirl (TECHWR-L) is a resource for technical writing and technical communications professionals of all experience levels and in all industries to share their experiences and acquire information.
For two decades, technical communicators have turned to TechWhirl to ask and answer questions about the always-changing world of technical communications, such as tools, skills, career paths, methodologies, and emerging industries. The TechWhirl Archives and magazine, created for, by and about technical writers, offer a wealth of knowledge to everyone with an interest in any aspect of technical communications.
You read through the other responses, but because I posted a recipe
rather than an explanation, you failed to see that I already offered
this solution when I said to first convert the image color mode to RGB
and then to Save As GIF.
Here's the explanation: GIFs are run-length encoded using indexed color.
Indexed color means that each pixel can only be one of 256 color and
thus each pixel can only require an 8-bit byte to encode it. Pixel 1 is
color 17, for example. The colors are stored in a table of up to 256
24-bit words, each of which encodes RGB values between 0 and 255 (one
byte for the R value, one byte for the G value, one byte for the B value).
Run-length encoded that means is that instead of using one byte per
pixel, it specifies a color from the table (number 17, say) and then
says how many pixels are that color before changing to another color. So
if you have a horizontal stripe of a constant color, the GIF only has to
specify the color once and then just add another byte to say that the
color applies to the next 39 pixels, for example, yielding further
compression. (This works only in horizontal solids. Vertical stripes
don't afford much in the way of compression.)
When an RGB image is converted to GIF, all those subtle shades have to
be reduced to the most prominent 256 colors. The process is called
dithering and the result is a dithered imaged. Think about what it means
to dither. Do I want the apple pie or the chocolate cake? Pie or cake,
pie or cake, pie or cake. Gee, I can't make up my mind. Picture my head
swinging side to side while I choose. That's dithering (the original
meaning). Well, it's the same thing here. I'm really chartreuse. Should
I be yellow or should I be green? I can't decide, so I'll be half yellow
and half green (by coloring adjacent pixels different colors to average
the target color).
Dick
c -dot- sharp -at- meridio -dot- com wrote:
I've read through the other answers to this, and there's something
no-one's mentioned, but I've found beneficial when resizing.
GIFS are 256-colour (8 bit images). If, in whatever application you're
using (I'm a PaintShop user), boost this up to 16 million colours (16 bit)
before resizing, you'll get a better quality image, even though it's
reduced back down to 256 colours when you save it as a GIF.
I can't think how to technically explain why this works (fine tech writer
/I/ am!) but it's basically due to the way any blurred parts of the image
change in colour when they're resized. Using 16 million colours allows for
smaller differences in colour between area.
---
[This E-mail scanned for viruses at mail.fiam.net]
