In addition to reliable text recognition, page segmenting is an essential performance feature of text recognition systems that is, the interpretation of contextual information such as columns, blocks of text, and graphics. Further features are deskew, segmenting of individual units, and recognition of types of handwriting and signatures or of more than one language in the same document. In other words, if there are more than 4 or 5 mistakes per 1,000 units, processing by hand is more economical. Reliability of text recognition depends essentially on the background, the kind and size of the writing, and the contrast between text and background. Disruption of text recognition occurs when there is dirt on the material and omissions from the image information caused by incomplete or irregularly printed letters.
Reliability also depends on the density of the image information.
The greater the amount of image information being processed, the higher the recognition rate. Higher resolution in digitizing can therefore improve the recognition rate, as with digitizing in gray scale. In principle, the quality criteria we have mentioned also apply to microfilm. The correct standard background density and minimal ground shade are important to achieve high resolution and adequate contrast. Digitizing negative film avoids the disruption caused by dirt and scratches.