   Accessing pixel data and change the RGB values
  I am trying to access pixel data from the frame buffer object and then change the pixels' red components' value (ex. set 0.th byte to 0 or 1). How can I do this faster??Thanks   
  As you use a framebuffer object, I guess you'll have no problem using the data as a texture. Then take this texture (A) and one (B) which contains the data that you want to insert into the red channel. Write a pixelshader that takes red from texture B and the rest from texture A. Set up a framebuffer object to write to a new texture C.Now paint a quad that covers the screen and have your result in texture C.That way you don't have to mess around with the pixel data on the CPU and as a result, this should be quite fast.   