Computerized comparison of two autoradiographs.

Our laboratory previously reported (Anal Chem 55: 2345-2348, 1983) the development of a digitizer and FORTRAN program for display and quantification of digitized autoradiographic images. We have since added several capabilities to the program. Coarse "rubber sheeting" (i.e., transforming coordinates to superimpose images) of the image by a quadratic transformation of pixel coordinates is developed from interactive identification of a few matching spots. The program determines thresholds to display a given proportion of the total protein in the image, or a given number of proteins, and it creates a protein list containing the spatial coordinates of each protein with a peak value above this threshold, together with the amount of the protein as measured by the ratio of its integrated intensity above its half-maximum to the total integrated intensity of the image. The lists can be stored on a disk and are used as the primary data for fine adjustments to superimpose images, quantitative comparison of images, and abstract display of proteins. Methods are discussed for presenting comparisons between gels in cases where spots for many proteins change in intensity.