16 bit vs 32 bit color question

[!Allen Lasting]

I have the option of 256, 16 million, or 32 million colors on this P166, 64
meg ram, 2 meg video card, system.

I assume each one uses more processing power than the previous one. Is that
true?

If so, how much computing power to you save if you use 16 vs 32?

256 vs 16?

Or doesn't it really matter.

TIA

A

[Ingeborg]

"!Allen Lasting" > wrote in
:

> I have the option of 256, 16 million, or 32 million colors on this
> P166, 64 meg ram, 2 meg video card, system.
>
> I assume each one uses more processing power than the previous one.
> Is that true?
>
> If so, how much computing power to you save if you use 16 vs 32?
>
> 256 vs 16?
>
> Or doesn't it really matter.
>
> TIA
>
> A
>
>
>

Windows internally uses 16 million colors, for each base color (Red,green
and blue) 256 levels, which makes the total number of colors 256*256*256=
16M.

This is 3 bytes per pixel (24 bits), but for addressing reasons it's
easier (=faster) to use 4 bytes per pixel. This is the 32 bits modus.
This is _not_ 32 million colors. In this modus the 4th byte is not used.

Since your card doesn't have much memory, I suppose that your '16
million' in fact is a 16 bits mode. In this mode 5 bits are used for each
base color), which makes 15 bits + 1 dummybit = 2 bytes. The total number
of colors is 32*32*32=32k. (Maybe 64k if the dummy bit is used to give
green (which you see the best) extra depth.

When using 256 colors windows uses a look up table called palette to map
256 out of the 16M, so can adress them with a value between 0 and 255,
which is only 1 byte. This modus costs less memory (on the videocard, and
in the windows buffers) but windows each time must reacon the most
optimal palette, and map colors which doesn't fit to the best neighbour.

So what is the fastest? Theoretically the 32 bits modus is the fastest.
The system doesn't have to reacon anything, just copy the color to the
video memory. 24 bits is a good second. The system still just have to
copy, but the memory manager is not pleased with the 3 bytes addressing.
The 16 bits mode costs some more reaconing, but it's only some shift
actions (which goes very fast).
The 256 color mode (8 bits) uses the most computing power.

But in memory usage it's reversed. So if your computer is low on memory
(much swapping) the 256 color mode can turn out to be the fastest. But
most likely the 32 bits modus is the fastest. And it gives the best
results too.