Does (:,:,1) code work to calculate Y component in YcbCr color model?

i am currently studying color models in matlab specially YCbCr color model. I had an RGB image. First i converted image into YCbCr by using code rgb2ycbcr. then i used (:,:,1) to see the luma component of the image. is the value i am seeing the actual value of image luma? Anyone out there to comment on it?

Thanks

Answer 1

[Image Analyst]

Almost. Y is the luminance. Y' is the luma. See wikipedia: http://en.wikipedia.org/wiki/Ycbcr

Actually for an RGB or gray level image, the light collected actually has units of lumen*seconds. But that's only if you're interested in what the physical units would actually have. I can explain it further (like I've done here before) if you're interested. It often doesn't matter when doing image analysis and you can often find stuff just fine without knowing the actual real world units.

[Youssef Khmou]

Image Analyst, Suppose we are studying the Red-shift of the light based on RGB samples ("photometry") can we only focus on the R block? eventually Y' in ycbcr space?