8 or 16 bit for retouching

An 8 bit pixel has greater pixel depth or bit depth and can contain and display much more colour information. As each bit has two choices, 8 bits have 2x2x2x2x2x2x2x2 or 256 choices, which means 2 to the power of 8 or 256 colours. A complete image which is only 8 bit is likely to be a greyscale or an indexed colour image.

A colour image in this category will have 8 bits on each of the red, green and blue channels.
The total pixel content of the image combine to make the file size. An 8 bit pixel uses one 'byte' of computer memory and a thousand bytes amount to one 'megabyte' of memory.

The greater the bit depth or pixel depth in this 'rod' of digital information, the greater will be the number of colours and information stored. Therefore, the digital image will give a more accurate representation of the original.

Photoshop CS can handle most functions in 16 bits per channel, or a 48 bit image. Earlier versions of Photoshop can handle only a limited range of tasks in 16 bit, while Elements will work in an 8 bit per channel image.

Many scanners can scan film in 16 bit per channel mode and this will capture considerably more information and hence more colours, tones and details. In actual fact, Photoshop works in 15 bit + 1 unit, which amounts to 215. This produces 32,769 values, which is still considerably more than in standard 8 bit mode.

Lesson by:
Phillip McCordall