(March 13, 2013)

For those using Photoshop to produce professional looking images and so on the following should be basic information before you start your project.

Bit:  Binary digit, a digit in the binary coding system that is it is a 0 or 1, smallest or basic unit of information. A pixel on the hand is the basic unit of color on computer display It is defined as a unit of color and its location.  Thus a pixel can contain one only one color and is  square or (rectangular) shaped.
. 1 bit = 2 colors that is n bits = 2^n colors for example 8 bits will contain 2 to power 8 colors which is exactly 256 colors.
Other terms to be familiar with are:
A color as displayed onscreen is combination of RBG (Red Blue and Green). The intensity (percentage or how much ) of  Red , Blue or Green in a color determines what color appears on the screen.

An Image (still image) on the other hand is that that depicts visual perception.  Photoshop is especially used for bit-mapped images over vector graphics .
Image resolution is the number of pixels that make up a printed out inch. The higher the resolution the clearer the printed out version of the image this of course with respect to the capabilities of your printer.
Because image size (  its appearance )onscreen differs according to size of monitor zooming and out  etc  image size on screen is measured in pixels over manual use of your ruler to try and measure the size of the image on screen.

Print resolution: density of pixels on a printed page.

The relationship between an onscreen image and its printed out version is that:

On Screen Size/ Resolution = Printed Width

For example for an image with Screen size 200 pixels and resolution 100 pixels will be with width 2 inches.  If the resolution is higher then the same screen size will be smaller once printed out .

Using the Information In Photoshop

The main purpose of knowing how many colors in a pixel or the resolution  is for print out purposes to prevent the frustration of discovering that your project looks better (bigger) on screen than on your hard-copy.

Note that image resolution should be set before starting because it defines how many pixels per inch an image will have changing the image’s resolution after creating it will distort it on the hand the pixels can be changed. However while working with vector graphics this restriction is void because the image will retain its quality irrespective of the scaling direction.