Translation of printed lettering into braille characters - with standardised contrast of letters against background

摘要

By the use of a photo-optical scanning unit a definite area of the reading copy, book or newspaper, is scanned point-by-point, by lines or by areas and the maximum and minimum signals obtained are assigned by suitable threshold switches to white and black surface elements. The signals corresponding to the black-and-white distribution of the character to be read control a two-dimensional light emitter arrangement. A high-contrast image of the printed characters is obtained. By appropriate adjustment of the threshold switches an image of uniform quality is always obtained, even though the print quality is of varying contrast and the paper has different degrees of reflection.