Selecting an appropriate scale factor is useful for both speed
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.