What kind of function allow me to find out the colour RGB components of any given pixel?

What kind of function allow me to find out the colour RGB components of
any given pixel?

References

Reference NO 1

http://stackoverflow.com/questions/13646911/what-kind-of-function-allow-me-to-find-out-the-colour-rgb-components-of-any-give

Reference NO 2

http://php.net/manual/en/function.imagecolorat.php

Reference NO 3

http://en.wikipedia.org/wiki/RGB_color_model

Reference NO 4

http://lodev.org/cgtutor/color.html

Reference NO 5

http://www.pygame.org/docs/ref/surface.html

Reference NO 6

http://docs.gimp.org/en/glossary.html

Reference NO 7

http://rsbweb.nih.gov/ij/docs/menus/image.html

Reference NO 8

http://99designs.com/designer-blog/2012/02/21/correct-file-formats-rgb-and-cmyk/