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Colour is represented as data on your computer and is stored as a varied number of colours per pixel on screen for each graphic image. For example 1-Bit Colour means that each pixel is represented by one bit only(black or white). |
The table below covers common colour formats(pixel depths) and how they are represented in terms of the number of bits versus the number
of colours displayed. It also gives a comparison of the same image and how it looks under the different pixel depths.
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24 Bit Colour (True Colour) 16.7 million colours |
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16 Bit Colour 65.5 thousand colours |
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8 Bit Greyscale 256 shades of grey |
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8 Bit Colour 256 colours |
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4 Bit Colour 16 colours |
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1 Bit Colour 2 colours |
We can tell straight away that there is a direct relationship between data and colours and by rule of thumb, the more colours there are displayed, the
higher the amount of data stored in an image.
When comparing the actual images of actor Jim Cary, it's very hard to determin the difference between the 24 bit and 16 bit colour images, however we
can notice drastic changes once we use pixel depths of 8 bit or less. You can notice that the 8 bit colour image is starting to look a little "grainy" or
pixellated, this is because of the number of colours that are displayed at one time.
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Take a look at these "close ups" to the left. The top image is 24 bit, the middle image is 8 bit and the bottom image is 4 bit.
The original image is in "true colour" and contains over 16 million colours whereas the 8 bit image is trying to display the same
image, but using only 256 colours instead of 16.7 million.
The effect is even more severe for the 4 bit image as you are trying to display the original true colour image with only 16 colours!
4 bit colour is hardly ever used now as entry level computers are now more capable of displaying imagery with higher pixel depths but
4 bit pixel depth is still used to generate smaller icons or images that have less detail. |
ith computerised imagery, colour can be described through the use of Colour Models. The models are used to give colour a tangable numeric value
or format. One such colour model type is the RGB(Red, Green, Blue) format which can represent all of the available 16.7 million colours as a numeric
amount. The RGB model can represent a colour by giving a value ranging between 0 to 255 for the red, green and blue settings, that is a total of 256 different
values for each setting and a total of 16,777,216 different combinations for all 3 settings. So for example the colour black is represented on the RGB model as
Red=0, Green=0, Blue=0 and white is represented as Red=255, Green=255, Blue=255.
Below is another "close up" of Jim Carey but with additional colour samples taken from a pixel on the cheekbone and the front tooth. Included with each pixel sample is its respective RGB model value.
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Red=80, Green=35, Blue=2 |
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images © 1994 New Line Cinema |
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images created by Industrial Light and Magic |