32 bit colour

[nicko]

Can anyone help me out on the performance/graphics benefits of using 32 bit colour. I have been led to believe that rendering a game in 32 bit colour slows down the game, and i can't see how you could really tell the extra colours?

Also, when reviews quote 100+ frame per second readings, what is the practical point of this? can you really tell the difference if its more than about 50 FPS? Or is it a general benchmark for future reference.. it just sounds silly when people say.. ooo look it dropped below 200 FPS.. :?

[mungo]

32-bit color is important for allowing the computer to do effective transparancies. The framerate issue is more about anything under 30fps will affect your performance.

[nicko]

um, thanks mungo... XD ;D :offchops: :?

[mungo]

sorry had two reply windows open and got them mixed up. And reviews where the framerate is at those levels are mostly hardware reviews, this shows how the hardware performs in a quantative way to allow comparisons.

[nicko]

ok cool thanks :)

[MattD]

32 bit colour is not actually 32 bits of colour

theres a multitude of ways to encode the colour information the most common are RGBA with 8 bits per channel and RGBA with 10 bits for each colour and 2 bits for the alpha channel.

at 8 bits per channel that gives you a total of 255 discrete levels of each colour component, which in turn allows a total maxiumum of ~16 million colours (24bit colour basically). then in turn there are 255 discrete levels of transparency associated with that colour

in 10 bit colour mode, there are a total of 1024 shades of each colour component, allowing for a total of ~1000 million colours
however there is only a total of 4 unique alpha states (including opaque)

in 16 bit colour mode, pixels are packed in (RGBA) 5551, 5650, or 4444 colour modes.

so at a maxiumum you are limited to 65536 different colours (each with max of 32 or 64 (bit) discrete colour component levels)

why am i going through all this.. well 32 bit colour looks a shitload better, because you get 244x more colours, but you also pick up 255 discrete levels of transparency

what the fuck does that mean i hear you ask.

next time you shoot a rocket at something, check the smoke trails. in 32 bit, youll be able to see through the trails in a very smoke like way thanks to all the extra alpha information contained in the smoke texture. In 16 bit, the lack of an alpha channel (or a very small one) mean that the transparency is nowhere near as photorealistic as it is under 32 bit (and the colours arent quite as nice...) for another test, try looking through water in q3, youll see that things are a LOT clearer and sharper under 32 bit than in 16bit.

not a lot of difference hey? well if your in it for the visuals, then 32 bit is great, if you want framerate then 16 bit is for you. remeber 32 bit basically doubles the amount of texture data your video card needs to deal with, and hence the slowdown.

your gfx card can only read/write so much memory in any particular clock tick, and as youve just doubled the amount of work it needs to do, its not going to be anywhere near as fast until memory bandwith increases.

for some more info on alpha go here (http://futuretech.mirror.vuurwerk.net/alpha.html)

Matt D
-= lookout my properller hat is whirring again =-

[MattD]

Originally posted by nicko

Also, when reviews quote 100+ frame per second readings, what is the practical point of this? can you really tell the difference if its more than about 50 FPS? Or is it a general benchmark for future reference.. it just sounds silly when people say.. ooo look it dropped below 200 FPS.. :?

ok, well theres two values, the first one is your monitor refresh rate. the second is your video cards total maximum frame rate.

the 200fps figures are calculated with whats called refresh synchronisation off. this means the video card is free to blurt as many god damn frames as it possibly can at the monitor.

doing this can (and often does) result in tearing or shearing which is the visible artifcats left behind as the graphics card renders more than one frame in a single monitor refresh.

what the fuck am i on about?

ok, well the monitor draws things from top left, to bottom right, moving right to the edge of the screen and dropping down a line. this takes a few milliseconds to do. your refresh rate dictates how often this happens. 85hz = 85 times a second. In quake, if you spin around REALY fast, its possible to see this change in orientation effect whats drawn on the screen mid frame.

so, the 200fps is just an indication of the maxium raw power the card can produce, if your monitor is set to an 85hz refresh rate, then the card should easily produce the required 85fps (in sync with the monitor) and youll still have a lot of frames left over for when things get hairy.

every person is different, i hate 50, 60 is just bearable, 85 is gold, over 85 i cant tell the difference...

Matt D

[nicko]

ok. that makes a lot more sense now, i might turn it back on to see what i have been missing. thanks for the explanations guys

[SpeedFrog]

Don't forget slowdown too - if your PC happens to slow down while rendering a complex scene, a PC running at 200FPS might only slow down to 80, whereas a machine running at 60FPS constantly might drop down to 20. Noticable difference.

[Morphee]

i can tell teh difference when im playing Q3 between 50, 80, 100 and 120 fps.
its got something to do with the refresh rate, blah blah, i cant remember, but you can tell.

ps, last lan i went to, some dude had a beasty Rig and got 745 fps AVRAGE in Q3 timedemo1

[MattD]

Originally posted by Morphee
i can tell teh difference when im playing Q3 between 50, 80, 100 and 120 fps.
its got something to do with the refresh rate, blah blah, i cant remember, but you can tell.

ps, last lan i went to, some dude had a beasty Rig and got 745 fps AVRAGE in Q3 timedemo1

i never thought id see someone in real life type like jeff k

Matt D
-= l33t like teh JeFF K! =-

[Morphee]

notice the posting time
5am, no sleep. My bad for all the typos, in the future, ill try to be much more liek yuo ok maens>???

[First Strike]

i cant tell the difference running 32 bit or 16

on my pc

when i run 16 as apposed to 32 i can notice the speed increase

(frames)

[MattD]

Originally posted by First Strike
i cant tell the difference running 32 bit or 16

on my pc

when i run 16 as apposed to 32 i can notice the speed increase

(frames)

you didnt read the thread did you :)

check out translucency and lighting under 16bpp and 32bpp thats where the bit depth comes into play

hell, 32bpp still isnt enough :)

Matt D