🚀 go-pugleaf

Florian Gutzwiller writes
> If I compare the color brillance of GIF prictures on a NeXT 16bit system 
> and a Sun 8 bit display the Sun is much more brillant. This is not a 
> monitor problem for sure. I'm using ImageViewer. 

Assuming that the Sun has 8-bit graphics that use a Color Look-Up Table (CLUT)  
to map to 24-bit color values, it's no surprise that GIF images look better on  
the Sun.

Basically, the NeXTstation color has 12-bit color, where these twelve bits  
actually represent the Red, Green, and Blue components at each pixel (4 bits  
apiece).  This is called true color.  This gives your NSC the ability to  
simultaneously display 4096 different colors from a palette of 4096 possible  
colors.

The Sun has 8-bit color, but those 8 bits are just used as an offset into a  
table of 256 colors, where each color in the table has 24 bits.  This is called  
indexed color.  Thus on the Sun you have the ability to simultaneously display  
256 different colors from a palette of 16,777,216 possible.

GIF files, as it happens, are stored the way the Sun displays images; ie each  
pixel is just an 8-bit index into a table of 256 24-bit colors.

When you display a GIF on an NSC, the 24-bit colors in the file must be  
approximated with 4096 colors the NSC has available.  So, obviously, when you  
have an image that can have a subset of 16 million distinct colors, and you try  
to display it on a monitor that can only show a subset of 4096 distinct colors,  
the image is going to look a little washed out.

When you display the GIF on the Sun, the Sun just sets its Color Look-Up Table  
to be the 256 colors in the GIF file, and VOILA you're displaying the original  
24-bit color values that are actually in the file.

Well, great, you say, why does anyone bother with this true color junk when  
indexed color gives you so many more colors?  Well, it doesn't, really.   
Indexed color gives you a nice large palette of colors, but you have to pick  
your 256 favorite of them.

Thus, images without a lot of different colors in them look great in indexed  
formats (like GIF), since you can have a lot more shades of the same color.   
Images with a lot of different colors will probably look better in true color,  
since you have the ability to display more different colors, even if the  
palette you are choosing from is smaller.

-William Shipley
The Omni Group
DBKit consulting, and now 3.0 image filtering

PS: PostScript also gives you dithering, which allows you to simulate having  
more colors by drawing two (or more) colors right beside each other and  
trusting your eye to blur them together as if they were one pixel.  Thus, if  
your GIFs look washed out, one solution is to magnify them and back away from  
your monitor.  (Another would be to buy a 24-bit true color board, like the  
NeXTdimension, but the former seems cheaper.)