Document Scanning

Image Types

1. Monochrome

For a simple monochrome scan, a pixel is simply black or white. This will give it a computer value of 0 or 1. Monochrome files are best for the vast majority of black and white line and text documents and for items that contain colour or tonal variation that is not important, such as in a printed letterhead. The files
are relatively small and the most easily handled by imaging application software.

2. Greyscale

This provides an image capture that is similar in effect to a black and white photograph. Each pixel is recorded as a shade of grey, with most scanners giving a range of 256 (or more) grey levels, or shades, from black at the dark end to white at the light end. Greyscale files retain the tonal detail of the original image. For documents where there is very low contrast between the line and the background, or where there is an illustration with tonal variation that is to be preserved, this file type is to be recommended. Greyscale files are much larger than monochrome files, and there are some limitations in their application.

3. Colour

The colour of each pixel is sensed as the red, green and blue components that go to make up that colour. This is similar to the way a colour is made up on a television or computer monitor screen. Whilst the sensing of colour is normally done in a full colour mode, scanners and associated image capture software can reduce the number of colours and thus the file size of the image.

Colour files retain the colour and tonal variation of the original and represent, effectively, an electronic copy of the master document.