Matlab - extract pixel RGB value from multiple images at once

I have about 2300 images that I'd like to extract the pixel value of each for at the 0,0 location. I would then like to take those pixel values and create a colour spectrum with them in order from lightest to darkest (or vice versa). Where there are multiple pixels of the same RGB value, the band should be thicker (I want them each counted individually to show its prevalence). Each image is the same size.

I'm very new to Matlab, if you could provide step by step instructions that would be great!