Selecting an appropriate scale factor is useful for both speed and accuracy.

If images are very large they may take a long time to process. Reducing the size of an image can result in dramatic speed improvements without any loss in accuracy. In general you should be aiming at text with a height of about twenty pixels. So if your test is scanned at a resolution which results in a character height of forty pixels, a scale factor of 0.5 might be appropriate.

If text is very small, increasing the size of the image can result in dramatic improvements in accuracy of recognition. A scale factor of two results in major improvements. A scale factor of four results in further small improvements. Factors greater than this are not effective. Note that this type of upscaling is only appropriate in cases where the original image is available in grayscale or color - not in black and white.

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