236 colors on the screen

Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

However, I never see this mentioned in all the discussions of color in
this NG. Surely it affects how images look on the screen. For example,
if this is true, you can never display a grayscale with more than 236
different levels of intensity.

While this might be more than enough for a gray scale, when you put
all the colors in a photo on the screen, I would think the 236 color
limit would be important.

What am I missing?

TIA
Duncan

BioColor wrote:
Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

Today's video cards don't use palettes - they typically have 8 bits of
red, 8 of green, and 8 of blue. How long ago was your graphics
programming?

David

On Thu, 24 Feb 2005 16:28:49 GMT, BioColor wrote:

Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

However, I never see this mentioned in all the discussions of color in
this NG. Surely it affects how images look on the screen. For example,
if this is true, you can never display a grayscale with more than 236
different levels of intensity.

While this might be more than enough for a gray scale, when you put
all the colors in a photo on the screen, I would think the 236 color
limit would be important.

What am I missing?

What you are missing is a video card that was made in the last 10
years.

Where the hell are you? Elbonia?

Today's (and even those of 5 years ago) video cards are not limited by
this palette method any more, although they can still use it if you
wish, most people run their video cards in high-color (16 bit) or
true-color modes (24 bit) paletteless colors.

--
Owamanga!

In article ,
BioColor wrote:
Hi,

While this might be more than enough for a gray scale, when you put
all the colors in a photo on the screen, I would think the 236 color
limit would be important.

What am I missing?

Possibly the fact that for the last decade, consumer video cards have
allowed high resolution "true-colour" displays which don't indirect via a
256 entry LUT, but just allocate a 32 bit word for each pixel and store a
full RGB triplet in each one, allowing each pixel on the screen to take any
one of the 16,777,216 colours that exist in a 24 bit colour range?

256 color palletted color ?

As all of the other posters have mentioned, this hasn't been in use for
something like at least a decade. In fact, I have an old computer across
the room set up for Windows 95. It was upgraded from Windows for
Workgroups, version 3.11. It is at least ten years old. It has **always**
been set up for the so called "high-color" (16 bit) video mode.

What you are missing ... is about the last ten to fifteen years.





"BioColor" wrote in message
...
Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

However, I never see this mentioned in all the discussions of color in
this NG. Surely it affects how images look on the screen. For example,
if this is true, you can never display a grayscale with more than 236
different levels of intensity.

While this might be more than enough for a gray scale, when you put
all the colors in a photo on the screen, I would think the 236 color
limit would be important.

What am I missing?

TIA
Duncan

Kibo informs me that BioColor stated that:

Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

I don't think I've seen a PC with palette-based video in ten years or
more. Modern machines are usually 24 bit colour, & often 32 bit colour.

However, I never see this mentioned in all the discussions of color in
this NG. Surely it affects how images look on the screen. For example,
if this is true, you can never display a grayscale with more than 236
different levels of intensity.

While this might be more than enough for a gray scale, when you put
all the colors in a photo on the screen, I would think the 236 color
limit would be important.

The traditional method was to grab most of the palette, assign a very
carefully selected set of colours to it, & use error-diffusion dithering
to simulate 24 bit colour. (It worked surprisingly well if you were a
yard or more away from the screen.) Fortunately, we don't have to jump
through those sorts of hoops any more.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

I don't think I've seen a PC with palette-based video in ten years
or more. Modern machines are usually 24 bit colour, & often 32 bit
colour.

32-bit colour? Not heard that one before, how many bits are for RBG,
something like 10,12,10 ???

On Thu, 24 Feb 2005 16:55:40 GMT, Owamanga wrote:

Where the hell are you? Elbonia?

ROTFL


Today's (and even those of 5 years ago) video cards are not limited by
this palette method any more, although they can still use it if you
wish, most people run their video cards in high-color (16 bit) or
true-color modes (24 bit) paletteless colors.

Ah. Silly me. It's very cold here in Elbonia, and my brain must have
been frozen.

I take files of floating point numbers and, for display, I convert
them to those RGB intensities using a palette. With the image on the
screen, I interactively modify the colors by modifying the palette (in
my brand new Radeon card), instead of destructively modifying the rgb
intensities of each dot on the screen in a non-palettized mode.

Fortunately, all the new cards still support palettes.

The original code and concept are from 1975. After a bunch of ports
and rewrites, it finally ended up on a PC when you needed $8,000 worth
of extra hardware to show anything beyond monochrome. A few years ago
the 8-bit color other posters have recalled began to misbehave on the
newer cards, and I rewrote it to work in truecolor. I still use the
palettes, though, and they are still limited to 236 colors in VB.

Duncan

BioColor wrote:
Hi,

From my work with graphics programming, AFAIK a video card only has
256 entries in its active palette. 20 of these are reserved by
Windows. This leaves only 236 simultaneous colors for dots on the
screen at one time. Each of these colors has it's own r, g, and b
values. With 8 bits of intensity for each of those you get a
theoretical palette of 16 million colors from which you can select any
236 at a time.

This is actually correct (ish) for about, er, 1991, when my 1-megabyte
Trident 8900 video card could do 1024x768x8-bits and you paid zillions
of dollars for 24-bit graphics on an SGI.

What am I missing?


About 15 years.

pete
--
"Send lawyers, guns and money...."

scott wrote:

32-bit colour? Not heard that one before, how many bits are for RBG,
something like 10,12,10 ???

IIRC you use less bits for blue if you're doing 8-bit non-palette
graphics; I used to use the Research Machines colour graphics card in
the early 80s and that had 3 bits of red, 3 bits of green and 2 bits of
blue in its palette.

pete
--
"Send lawyers, guns and money...."