image analysis coding help

I have images like the one attached (sans the drawings which is evident when comparing right to left).
I am looking to quantify the gray scale pixel intensity(in this case represented in green) as defined by the red(arc) and yellow(line segment) boundaries.
So basically I would like to be able to define two line segments(Top1,Bottom1) (Top 2,Bottom2) and measure the intensity going down from a set pixel distance of 0 defined by the top arc between points Top1 and Top2 to a pixel distance defined between the corresponding point on the arc defined by bottom 1 and bottom 2(vertical line scan adjusted for angle). The idea is that I draw the arcs on the image and this will set the top and bottom and get line profiles of intensity across this area going from top to bottom( as shown in the example white lines). The end result is a graph with pixel distance on one axis and pixel intensity on the other.

Your help is appreciated.