在計(jì)算機(jī)圖形學(xué)領(lǐng)域時(shí)常聽(tīng)到gamma correction ，gamma correction 控制了圖像整體的亮度，reproduce colors也需要gamma correction的一些理論知識(shí)，gamma correction不僅僅是控制了圖像的亮度，而且還控制了RGB各個(gè)分量的比例，我們知道渲染器是線(xiàn)性的，而顯示器并非線(xiàn)性，其實(shí)電子打在屏幕上從而產(chǎn)生亮點(diǎn)，電子的運(yùn)動(dòng)受電壓控制，這兩者是指數(shù)關(guān)系的，所以產(chǎn)生的亮度也跟電壓成指數(shù)關(guān)系，而發(fā)送給顯示器的voltages范圍是0~1：
對(duì)于我們輸入的圖像，如果直接顯示，那么就會(huì)篇暗，根據(jù)已知電壓與顯示亮度的關(guān)系，進(jìn)行g(shù)amma correction ，其實(shí)就是對(duì)gamma曲線(xiàn)的修正。一般生產(chǎn)廠(chǎng)家不加說(shuō)明，他們的伽碼值大約等于2.5.
代碼：
gammaCorrection = 1 / gamma
colour = GetPixelColour(x, y)
newRed = 255 * (Red(colour) / 255) ^ gammaCorrection
newGreen = 255 * (Green(colour) / 255) ^ gammaCorrection
newBlue = 255 * (Blue(colour) / 255) ^ gammaCorrection
PutPixelColour(x, y) = RGB(newRed, newGreen, newBlue)
知道m(xù)onitor不是一個(gè)線(xiàn)性的，那么我們?cè)谶M(jìn)行顏色加法時(shí)，我們得到的顏色并不是真正的顏色值的相加，比如gamma factor是2.2
red = add (r1, r2);
red= add (0.235,0.156);
對(duì)于一個(gè)線(xiàn)性設(shè)備，red = 0.391,對(duì)于未經(jīng)修正的montior red=0.126;
因?yàn)橛幸粋€(gè)冪函數(shù)的運(yùn)算：C_out = C_in2.2
現(xiàn)在使用gamma correction :C_corrected= C_out1.0/2.2
0.3912.2 = 0.126
0.1261.0/2.2 = 0.39
我們看到使用伽碼校正以后我們能得到我們預(yù)想的顏色值0.39.
There are two ways to do gamma correction:
- Using the renderer. The renderer (the graphics card or GPU) is a linear device. Modern renderers have the support of gamma correction via sRGB textures and framebuffer formats. See the following OpenGL extensions for more details: GL_ARB_framebuffer_sRGB and GL_EXT_texture_sRGB. With these extensions you can get gamma corrected values for free but gamma correction factor is set to 2.2. You can’t change it.
- Using a software gamma correction. The gamma correction is applied to the final scene buffer thanks to apixel shader and you can set the gamma correction you want.
In OpenGL, using GL_ARB_framebuffer_sRGB is really simple: once your FBO is bound, just enable the sRGB space with
glEnable(GL_FRAMEBUFFER_SRGB);
gamma-correction