A low cost, microcomputer-controlled image analysis system is described which scans electrophoresis gels or photographic negatives with high resolution. Absorbing gels (e.g. with stained proteins) are analyzed using broadband or monochromatic visible light. The gel is scanned by a video camera with a macro objective; the gray level of each pixel is digitized sequentially and the values are stored in the computer memory. Repetitive scanning is used to average the absorption values before plotting on a digital plotter. Photographic negatives of gels and autoradiograms are scanned using the same technique. Fluorescent, non-absorbing gels (e.g. nucleic acids stained with ethidium bromide) are analyzed on a transilluminator with u.v. excitation radiation. The fluorescence intensity of each pixel is digitized and processed as described above.