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View Full Version : Weird thing with WinXP



yaro_dup1
07-12-2003, 12:39 PM
Hi,

I've changed my OS to WinXP and I saw that OpenGL (or Direct3D) programs are "darker" - scenes are very dark.
For example Quake 3 Arena with the same parameters looks much more lighter on Win98 then on WinXP. What's going on? I wrote a program without light sources and it's OK, but every game which using lights looks really dark, too dark in my opinion.

Thanks for help

dorbie
07-12-2003, 03:31 PM
Difficult to say.

It may be that the general specification of an sRGB display response happens to be darker than what you're used to on Windows 98 (I'm really not sure). The other thing that may be going on is you or someone else adjusted gamma on Win98 years ago and you just weren't aware of the implications.

Try going to Display->Settings->Advanced->Color Correction, and increasing the gamma factor there a bit.

Things should have an sRGB response 'officially' to display content correctly on a PC, so a little utility to help you adjust this (such as the one that ships with Photoshop) is useful to have.

There's a double interraction going on here to adjust this correctly, let me explain; When you display a linear scale of brightness on an 'average' monitor it appears non linear in brightness. The response is approximately a power function of 2.5 but it varies hugely. Now, this gamma response is exploited by content because your eye has a non linear contrast sensitivity it's a happy coincidence and content (from digital cameras, scanners etc.) can spend more bits at the dark end of the scale in the shadows to reduce visible banding and just assume it will look OK on most monitors. There was typically no intervention after creation, just an assumption of some display response unless you were using a professional package.

This has been going on for years, but it was never really formal, until a specification for a standard response on computer displays & formats called sRGB was agreed, with a power function of 2.2 (don't ask why not 2.5, it's complex and I don't fully understand why).

Anyway, the result is that with graphics cards supporting gamma correction, you should adjust your display card gamma correction so that the combined gamma response of the card and your unique monitor is around 2.2 to match the sRGB spec and everything will look as the content creators intended.

This is somewhat naive since there's more to this than simply gamma (there are phosphor colors, color temperature and other strange stuff we don't need to worry about too much unless we're pros), but if you get your black level correct and gamma response set at 2.2 you'll be in good shape for viewing most stuff intended for PC viewing.

Complicating things Apple computers have a gamma response of 1.8 not 2.2. In addition some content stores the built in gamma correction so it can be retargeted at any display instead of assuming the viewer has the same response display as the creator (PNG files support this number for example). If something doesn't have this gamma field then you may have to know it's source to view it as intended, for example if it was created on an SGI then you'd handle gamma differently from a Mac and from a PC :-). Generally a good asumption is that it was created on a PC, and some smart web authors tend to split the diffreence between Mac and PC w.r.t. the built in gamma response of their images (bit distribution on a non linear scale).

All that is really just background though, it sounds compex but the basics are very simple when you get your head around them. If you adjust your monitor so that black is black and really dark gray is barely but still discernably different from black and then you adjust your graphics card's gamma correction so your card + monitor combination has a gamma response of 2.2 you'll be 95% towards having a fairly decent display seup for viewing stuff on a PC.

[This message has been edited by dorbie (edited 07-12-2003).]