<Li> Normalise aspect ratio and scale </Li> <P> Segmentation of fixed - pitch fonts is accomplished relatively simply by aligning the image to a uniform grid based on where vertical grid lines will least often intersect black areas . For proportional fonts, more sophisticated techniques are needed because whitespace between letters can sometimes be greater than that between words, and vertical lines can intersect more than one character . </P> <P> There are two basic types of core OCR algorithm, which may produce a ranked list of candidate characters . </P> <P> Matrix matching involves comparing an image to a stored glyph on a pixel - by - pixel basis; it is also known as "pattern matching", "pattern recognition", or "image correlation". This relies on the input glyph being correctly isolated from the rest of the image, and on the stored glyph being in a similar font and at the same scale . This technique works best with typewritten text and does not work well when new fonts are encountered . This is the technique the early physical photocell - based OCR implemented, rather directly . </P>

Ocr devices read printed characters in an ocr font