Gamma correction slider - CodeProject®

Sample Image - Gamma_Manager.gif

Introduction

Gamma Manager is based on Gamma Slider control. This control allows to change gamma monitor on most graphic cards. The goal for this project is very simple and control is for VC6 & VC7.

The other day I downloaded a N64 emulator but the screen was so black that I did not see anything. I had thus to find this solution to lighten my screen. I know that the tools of my video chart make it possible to change gamma of my screen, but it is faster with this tool.

Implementation

The implementation of this slider control is very easy.

Import GammaSlider.h and GammaSlider.cpp into your project.
Include reference to the class control.
Add slider control on a form.
Use ClassWizard to declare variable name derived from CGammaSlider control.
That's it, enjoy!

Under the hood

Windows provides two APIs GetDeviceGammaRamp/ SetDeviceGammaRamp to perform gamma correction. In fact we need to have a 3 dimensional buffer of 256 WORD to manipulate gamma correction. To change gamma, it is necessary to change the RGB value of each color contained in the buffer by a float factor between 0.0 and 2.0.

Example

We need to save current gamma for future restore.

WORD m_RampSaved[256*3]; 
if (!GetDeviceGammaRamp(::GetDC(NULL), m_RampSaved))
{
    TRACE("WARNING: Cannot initialize DeviceGammaRamp.\n");
}

To change gamma, cycle into ramp buffer and change RGB color where Gamma is the float factor.

WORD ramp[256*3];
for( int i=0; i<256; i++ ) {
    ramp[i+0] = ramp[i+256] = ramp[i+512] = 
    (WORD)min(65535, max(0, pow((i+1) / 256.0, Gamma) * 65535 + 0.5));
}
SetDeviceGammaRamp(::GetDC(NULL), ramp);

Now to trap slider control message, we need to use a special message ON_WM_HSCROLL_REFLECT() that can provide message to be dispatched into control class itself.