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**D0ug** · 27 September 2002, 21:32

I guess noone knows about 15bit color? =(

**Kruzin** · 27 September 2002, 21:45

I guess not.
I know I've never used it myself.
Your best bet is to ask at the Matrox tech support forums when they open again on Monday...

**MarkV** · 29 September 2002, 13:20

D0ug,

Here's how to enable 15-bit color. It involves a bit of registry hacking.

First you need to find where the Matrox PoweDesk registry key is. It used to be as described in the PD readme excerpt that you posted, but I've found that it jumped around on WinXP, and maybe has on Win2k as well. Either way, there's an easy way to find it.

Go to HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\VIDEO. Under this key you will see one or more strings with the name \Device\VideoX, where X is a number that Windows has assigned to the particular video device. The string values for each of these devices tell you where in the registry to find the settings for that device. For example, my G400 under WinXP is at \Device\Video0, which has value \Registry\Machine\System\CurrentControlSet\Control \Video\{4EEE12F5-5F9C-4E59-94F9-A437DA8A4A14}\0000. Replace \Registry\Machine with HKEY_LOCAL_MACHINE and you will be able to navigate to each of the video device keys. When you find the key that has the value "Mga.SingleResolutions" you know you've found the correct key.

Ok, now that you're at the correct key, you need to do two things. The first is to add the registry value that the PowerDesk readme file says, which is a REG_DWORD "User.Enable15Bpp", and should be set equal to 1.

The second thing you must change is the REG_BINARY value called "Mga.PixelWidths". Your system probably has the hex values 08 10 18 20, which translates into 8, 16, 24, and 32 decimal. You need to edit this value and add 0F between the 08 and the 10 (0F hex = 15 decimal).

Incidentally, you can control the accessibility of the other color depths by creating REG_DWORDs of "User.EnableXXBpp" where XX = 8, 16, 24, or 32. These default to 1, so the only reason to add the keys would be to set them to 0 to disable a particular color depth. You would also need to remove the corresponding hex value from "Mga.PixelWidths" if you truly wanted to disable a particular color depth.

Good luck!

**MarkV** · 29 September 2002, 13:23

Whoops, forgot to add that after you make these changes, you need to reboot for them to take effect!

**D0ug** · 30 September 2002, 12:49

Thanks, it worked. on windows 2000 the key for the primary head is located HKLM\SYSTEM\CurrentContolSet\Services\G400DH\Devic e0 The secondary head is located at HKLM\SYSTEM\CurrentContolSet\Services\G400DH\Devic e1

**D0ug** · 30 September 2002, 13:25

BTW, the User.Enable15Bpp is not required. all you need to do is add 0F to Mga.PixelWidths.

I got curious and tried removing the User.Enable15Bpp, and 15bit still works, so all of them must default to 1, like you said for 8,16, 24, and 32bit color. I guess the only use for the key would be if you wanted to set it to 0 to disable that depth.

I also noticed that adding 0F to the Mga.PixelWidths under Device0 which is the primary head, also enables 15 bit color on the secondary head which is Device1. There is no Mga.PixelWidths under Device1. So now i have 8, 15, 16, 24 & 32 on the primary, and i have 15, 16, and 32 on the secondary. I know the reason there is no 24bit color on the secondary, is because the MAVEN chip dosnt support that. dunno about 8bit though, guess its probably the same reason.

Another experiment i tried was adding 00-20 to Mga.PixelWidths to enable every possible color depth. No luck though. On the next reboot windows defaulted to the safemode vga drivers, and poped up a dialog box saying the current drivers were written for a previous version of windows.

**Greebe** · 30 September 2002, 15:13

Several of us are curious as to why 15Bpp is neccessary? Would this be job related (what for?) or just for educational purposes?

**MarkV** · 2 October 2002, 16:58

D0ug--

Glad to see you played with some of the settings. I wanted to try that myself, but my system has a pretty long bootup time and I just didn't want to deal with all the reboots that are required to experiment. It's too bad Matrox didn't update the readme to reflect the change in the registry keys for these newer versions of PowerDesk. I guess not too many people play with 15-bit color.

Greebe-

For me it's just educational/experimentational. "Because it was there" kinda thing.

**D0ug** · 3 October 2002, 23:42

Originally posted by Greebe
Several of us are curious as to why 15Bpp is neccessary? Would this be job related (what for?) or just for educational purposes?

It was just something that i was curious about, after reading about the mention of enabling support in the readme. It is also buggy. If any of you have enabled 15bit, then this bug is what causes the horrable colors. Take a look at this post i have made in the matrox tech support forums http://forum.matrox.com/mgaforum/For...ML/001130.html

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G400 and 15bit color

G400 and 15bit color

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