how will be mean brightness of color image will be formulated in matlab

color image is of three channels, so how to calculate mean brightness of the image Do i need to separate each channel of color image and then calculate mean of the brightness say in LAB space i need to calculate mean of only L which represent luminance or brightness of image

Answer 1

[Thorsten]

If you have an Lab image as a 3D matrix with planes L, a, b, just use

meanbrightness = mean2(Lab(:,:,1))

If you have an RGB image, you can convert it to Lab using

RGB = imread('peppers.png'); 
cform = makecform('srgb2lab'); 
Lab = applycform(RGB, cform);