The question and comments are vague, but this is my answer to one interpretation -- i.e. to use a graph to illustrate the transformation made to the image data. Consider a simple gamma adjustment. We should see a simple power function.
inpict = imread('tire.tif');
outpict = imadjust(inpict,[0 1],[0 1],0.5);
[xx idx] = sort(im2double(inpict(:)));
yy = im2double(outpict(idx));
plot([0 1],[0 1],':','color',[1 1 1]*0.5); hold on
Note that you'll only be able to draw the curve over the range represented by the images. Consider an image with a much lower dynamic range.
inpict = imread('pout.tif');
outpict = imadjust(inpict,[0 1],[0 1],0.5);
[xx idx] = sort(im2double(inpict(:)));
yy = im2double(outpict(idx));
plot([0 1],[0 1],':','color',[1 1 1]*0.5); hold on
