The invention relates generally to a method and apparatus for electronic contrast valuation of two-dimensional transparent original images, in which the original images are electro-optically scanned by rows and columns, and, more particularly, to a method and apparatus in which the image signals, corresponding to the image elements or pixels, and possibly needing correction, are subjected to frequency filtering in a low-pass filter. The resulting low-pass signals are summed with corresponding high-pass signals obtained by subtraction of low-pass signals from the original image signals.
A method of this kind is known in principle in the video art. It is known generally that one can use electronic means to achieve an enhanced or improved image. In particular, methods have been described for eliminating high-frequency noise signals, while high-frequency image signals corresponding to high local frequencies are accentuated by amplification. One can thereby achieve, on the hand, a picture smoothing, and, on the other hand, a sharpening of the image.
The fundamentals of these methods are described in detail in the books Digital Bildverarbeitung, by F.M. Wahl, Springer-Verlag publishing house, Berlin/Heidelberg/New York, Tokyo, 1984, and Digital Image Processing, by W. K. Pratt, John Wiley & Sons, New York/Chicester/Brisbane/Toronto, 1978.