Graphic Interchange
Format (GIF)
(.GIF file extensi=
on)
There have been raging debates about the pronunciation. The designers of G=
IF
say it is correctly pronounced to sound like Jiff. But that seems
counter-intuitive, and up in my hills, we say it sounding like Gift (witho=
ut
the t).
GIF was developed =
by
CompuServe to show images online (in 1987 for 8 bit video boards, before J=
PG
and 24 bit color was in use). GIF uses indexed color, which is limited to a
palette of only 256 colors (next page). GIF was a great match for the old 8
bit 256 color video boards, but is inappropriate for today's 24 bit photo
images.
GIF files do NOT s=
tore
the image's scaled resolution ppi number, so scaling is necessary every ti=
me
one is printed. This is of no importance for screen or web images. GIF file
format was designed for CompuServe screens, and screens don't use ppi for =
any purpose.
Our printers didn't print images in 1987, so it was useless information, a=
nd
CompuServe simply didn't bother to store the printing resolution in GIF fi=
les.
GIF is still an
excellent format for graphics, and this is its purpose today, especially on
the web. Graphic images (like logos or dialog boxes) use few colors. Being
limited to 256 colors is not important for a 3 color logo. A 16 color GIF =
is a
very small file, much smaller, and more clear than any JPG, and ideal for
graphics on the web.
Graphics generally=
use
solid colors instead of graduated shades, which limits their color count
drastically, which is ideal for GIF's indexed color. GIF uses lossless LZW
compression for relatively small file size, as compared to uncompressed da=
ta.
GIF files offer optimum compression (smallest files) for solid color graph=
ics,
because objects of one exact color compress very efficiently in LZW. The L=
ZW
compression is lossless, but of course the conversion to only 256 colors m=
ay
be a great loss. JPG is much better for 24 bit photographic images on the =
web.
For those continuous tone images, the JPG file is also very much smaller
(although lossy). But for graphics, GIF files will be smaller, and better
quality, and (assuming no dithering) pure and clear without JPG artifacts.
If GIF is used for
continuous tone photo images, the limited color can be poor, and the 256 c=
olor
file is quite large as compared to JPG compression, even though it is 8 bit
data instead of 24 bits. Photos might typically contain 100,000 different
color values, so the image quality of photos is normally rather poor when
limited to 256 colors. 24 bit JPG is a much better choice today. The GIF
format may not even be offered as a save choice until you have reduced the
image to 256 colors or less.
So for graphic art=
or
screen captures or line art, GIF is the format of choice for graphic image=
s on
the web. Images like a company logo or screen shots of a dialog box should=
be
reduced to 16 colors if possible and saved as a GIF for smallest size on t=
he
web. A complex graphics image that may look bad at 16 colors might look ve=
ry
good at say 48 colors (or it may require 256 colors if photo-like). But of=
ten
16 colors is fine for graphics, with the significance that the fewer numbe=
r of
colors, the smaller the file, which is extremely important for web pages.