Why does GetDeviceGammaRamp always return false

Question

I want to get the gamma value of the monitor, my code is below, but bget keeps FALSE, how can I tell where the problem is?

WORD gArray[3][256]; 	HDC hdc = GetDC(NULL); // 得到屏幕DC   	
int client_width = GetDeviceCaps(hdc, HORZRES); // 宽   	
BOOL bget = GetDeviceGammaRamp(hdc, gArray);   // 得到当前Gamma  	
ReleaseDC(NULL, hdc); // 释放DC

Answer 1

I want to get the gamma value of the monitor

You can use GetVCPFeatureAndVCPFeatureReply with VCP code = 0x72 for Gamma (details : https://milek7.pl/ddcbacklight/mccs.pdf)

(works on my monitor, Philips 247ELH)