Library for basic image manipulation in C++

Question

I am looking for a great C++ library for doing basic image manipulation. What I need done is to be able to convert an image to grayscale and have access to read the pixels of the image.

I have looked at OpenCV, GIL, CImg and Magick++, but either they were not too great, or I couldn't figure out how to convert an image to grayscale with the library.