Patent US 4,323,973

In a radiograph enhancement technique, useful in angiography and the like, a digitized subtracted image is obtained from the combination of a first and second radiograph, said second radiograph taken after the introduction of a radiographic contrast medium into preselected portions of a subject anatomical area. The subtracted image may be formed photo-optically, electronically or digitally. The digitized subtracted image is then stored as a matrix of points or pixels. The matrix representation is processed by unique software to enhance contrast by testing each pixel against a variable threshold and altering its value based on the results of that test. Once enhanced, the image is reconverted to analogue form and displayed via standard video analogue modules. The resulting display may then be photographed to preserve the image.