How to change gamma and brightness values for multi monitor setups

Question

How to change gamma and brightness values for multi monitor setups

sValentin 81

I'm trying to add a functionality to my app with which you can change gamma and brightness of any monitor connected.

For gamma I was looking at GetDeviceGammaRamp / SetDeviceGammaRamp, but on that page it says: "We strongly recommend that you don't use this API.". So, in this case, what else should I use to be able to change gamma for multi monitor setups?

As for brightness I was looking at GetMonitorBrightness / SetMonitorBrightness, but these also have a warning. Is there something else to use for this? Like with gamma I need something that supports multi monitor setups, and not changing the values for all monitors the same.

I'm only interested in Windows support, and no other OS.

Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2023-10-17T07:11:20.23+00:00

We strongly recommend that you don't use this API (GetDeviceGammaRamp / SetDeviceGammaRamp). Use of this API is subject to major limitations. For more information, you could refer to the Doc: https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-setdevicegammaramp

3 answers

Your answer

Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2023-10-17T07:11:20.23+00:00

We strongly recommend that you don't use this API (GetDeviceGammaRamp / SetDeviceGammaRamp). Use of this API is subject to major limitations. For more information, you could refer to the Doc: https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-setdevicegammaramp

Answer 1

Castorix31 90,686

With SetVCPFeature

(for example, Gamma : VCP code = 0x72)

sValentin 81 Reputation points

2023-10-10T10:03:11.1466667+00:00

I see that it has the same warning as with Get/SetBrightness. Is there a way to test if it supports it via software? Will GetVCPFeatureAndVCPFeatureReply fail and that means the function won't work correctly?

Also, for brightness should I use GetMonitorBrightness / SetMonitorBrightness, or SetVCPFeature with code 0x10? (at least that is the code I found in this image)
Castorix31 90,686 Reputation points

2023-10-10T10:31:03.39+00:00

You can test with CapabilitiesRequestAndCapabilitiesReply

or with a tool like ClickMonitorDDC (download on Google) which uses VCP codes
Castorix31 90,686 Reputation points

2023-10-10T11:10:30.8933333+00:00

BTW, MS doesn't recommend SetDeviceGammaRamp but DCCW.exe calls it...
sValentin 81 Reputation points

2023-10-10T12:04:58.6833333+00:00

I was wondering if that was Microsoft way of saying, "Just use our tools that are now available in Windows".
Thanks for your help.
sValentin 81 Reputation points

2023-10-10T16:41:32.47+00:00

It seems that SetVCPFeature actually has a lot of limitations when it comes to hardware, and that warning is right to be there. I tried it on an old monitor (where in the past I used SetDeviceGammaRamp and it worked) and the function doesn't work at all, and on a different one, IPS around $150, so not a high end one, but a price most people would look for, it says that the display doesn't accept that VCP Code.

So I would like a different way to change the Gamma and Brightness, as SetMonitorBrightness also uses the same principle as SetVCPFeature.
Castorix31 90,686 Reputation points

2023-10-10T17:43:49.8333333+00:00

VCP code for Gamma is not supported either on my PC, but the one for Brightness (0x10) is valid

You can do like DCCW seems to do : if a VCP code is not supported, it calls not recommended APIs like SetDeviceGammaRamp, ...
sValentin 81 Reputation points

2023-10-11T07:19:13.4166667+00:00

The thing with either SetVCPFeature or SetMonitorBrightness (which in the background I think they do the same thing for brightness), they are getting and setting the brightness straight on monitor settings, and not as a software change (hence the warning about VESA). That is why gamma was failing because in monitor settings, there isn't gamma for my model as value, only as profiles.

I have an MSI motherboard and for it's utilities they have "True Color", which allows you to change gamma and brightness, but they are both software changes, which means in order for them to be set, the program has to run at least once when Windows starts. And this is what I'm looking for, to remove the monitor from calculation entirely. And it isn't hard to make a program start with Windows, set the change and then it can close.

I tried to use GetDeviceGammaRamp but I'm getting the following error, I tried with #include <Windows.h>, #include <wingdi.h>, #pragma comment(lib, "gdi32"), but still the same error.

Castorix31 90,686

It returns TRUE on my old monitor (Philips 247ELH PHLC085) :

HDC hDC = GetDC(NULL);
WORD nGammaRampOld[3][256];
BOOL bRet = GetDeviceGammaRamp(hDC, static_cast<LPVOID>(nGammaRampOld));
if (bRet)
{
	// Code...
}
ReleaseDC(NULL, hDC);

sValentin 81 Reputation points

2023-10-11T08:11:19.8066667+00:00

I have an app made in 2018 and back then it was working, but now I tried it as I still have it, and it doesn't work anymore. It is using GetDeviceGammaRamp / SetDeviceGammaRamp. At that time I think I was using Windows 10, and now I have Windows 11. I didn't add any error print to it as I made it for personal use, so it might have the same problem with the module or not, I can't say. I don't have the code for it anymore.
sValentin 81 Reputation points

2023-10-17T15:22:23.7566667+00:00

It turns out that the problem has to do with having more then one monitor. Back then I had only one, and didn't had problems with it, but now I have two monitors and GetDC() can fail. I found something about using CreateDC(), but I have to do some more research on that first.
sValentin 81 Reputation points

2023-10-17T15:42:12.4533333+00:00

//Edit: Copy of last message, wasn't posted until I did it again... And now they both appeared.

Castorix31 90,686

I have only 1 monitor, but maybe you could do something like :

					DISPLAY_DEVICE dd;
					ZeroMemory(&dd, sizeof(DISPLAY_DEVICE));
					dd.cb = sizeof dd;					
					for (int nDevice = 0; EnumDisplayDevices(NULL, nDevice, &dd, 0); nDevice++)
					{
						if (dd.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP)
						{
							HDC hDC = CreateDC(NULL, dd.DeviceName, NULL, NULL);
							if (hDC)
							{
								// Code...
								DeleteDC(hDC);
							}
						}
					}

sValentin 81 Reputation points

2023-10-20T19:26:21.1066667+00:00

Thanks for your help, see my answer, it has solution for multiple monitors as well.

Answer 2

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Answer 3

I already posted an answer, but again it seems that it didn't got actually posted here, just like the comments. It says it is posted, but it doesn't appear. I already found a solution for when you have multiple monitors. I'll post parts of the code again as I don't have the full code I posted before with all the explanations:

General function:

static int hasAttachedScreen(int monitorIndex) {
	DISPLAY_DEVICE display{};
	display.cb = sizeof(DISPLAY_DEVICE);
	int ok = EnumDisplayDevicesW(NULL, monitorIndex, &display, 0);
	return ok != 0 && display.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP;
}

To set gamma:

BOOL setGamma(int monitorIndex, double gamma[]) {
	HDC hdc = GetDC(0);
	if (hasAttachedScreen(monitorIndex)) {
		DISPLAY_DEVICE display{};
		display.cb = sizeof(DISPLAY_DEVICE);
		EnumDisplayDevicesW(NULL, monitorIndex, &display, 0);
		hdc = CreateDC(NULL, display.DeviceName, NULL, 0);
	}
	else {
		hdc = NULL;
	}

	if (hdc != NULL) {
		WORD ramp[256 * 3]{};
		for (int i = 0; i < 256; i++) {
			ramp[i] = (WORD)gamma[i];
			ramp[i + 256] = (WORD)gamma[i];
			ramp[i + 512] = (WORD)gamma[i];
		}
		BOOL result = SetDeviceGammaRamp(hdc, ramp);
		ReleaseDC(0, hdc);
		return result;
	}
	else {
		return false;
	}
}

To get gamma:

void getGamma(int monitorIndex) {
	HDC hdc = GetDC(0);
	if (hasAttachedScreen(monitorIndex)) {
		DISPLAY_DEVICE display{};
		display.cb = sizeof(DISPLAY_DEVICE);
		EnumDisplayDevicesW(NULL, monitorIndex, &display, 0);
		hdc = CreateDC(NULL, display.DeviceName, NULL, 0);
	}
	else {
		hdc = NULL;
	}

	if (hdc != NULL) {
		WORD ramp[256 * 3]{};
		BOOL result = GetDeviceGammaRamp(hdc, ramp);
		ReleaseDC(0, hdc);
		if (result) {
			// Code...
		}
		else {
			// Code...
		}
	}
	else {
		// Code...
	}
}

//Edit: I don't know why but my messages aren't getting posted right. Maybe it is the website, or a problem with my account, I don't know. When I posted this answer the code I added for set gamma only contained function header...

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How to change gamma and brightness values for multi monitor setups

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