Photoshop
Digital Graphics
Colour Space
A colour space is a model for representing intensity values in colour. In other words, a colour space defines a colour model with a specific range of colour (also known as gamut *) that can be expressed in different ways, depending on how the colour is to be used. For example, the RGB * colour space is used for monitors, while the CMYK * colour space is used for printing. You can have the exact same colour of green for a monitor and for a printing press, but they will be described in different ways.
Within a colour model, there can be differently defined colour spaces. The RGB colour model, for example, can have several different colour spaces within it: Apple RGB, Adobe RGB, or sRGB. They all describe colour by the same method (Red, Green, and Blue axis), but they each have a different range (gamut) of colour that they can describe, depending on what they are being used with or for.
Distinctive colour spaces will have different methods of representing the same colour, providing inconsistent visual results. That is why it is very important to identify and distinguish the colour space that applies to digital graphics on the Web. For the purposes of digital graphics for the Web, we will concentrate on how Photoshop uses the RGB colour space.
The RGB Colour Space
The RGB (Red, Green, Blue) space is a three-dimensional colour space whose components are the red, green and blue intensities that make up a given colour. RGB-based colour spaces are the most commonly used colour spaces in digital graphics, because the majority of colour displays directly support them. The colours produced by an RGB colour space vary from device to device. They are referred to as device-dependent colour spaces.
Device-Dependent Colour Spaces
Device-dependent colour spaces enable the specification of colour values that are directly related to their representation on a particular device. In other words, a monitor can understand a certain gamut of colours, while a different device, say a scanner, can understand a different range of colours. Each has a colour space that it can work with, and that specific colour space is dependent on that specific device. This image shows Photoshop's RGB Colour panel.
Device-Independent Colour Spaces
A device-independent colour space is a colour model that does not depend on any specific device, but rather what the human eye (on average) can see.
How Colours are Displayed
We work in the RGB colour space daily when using computer displays, scanners and some printers. Here again we show a close-up of a monitor's phosphors. A pixel consists of a red, green and blue phosphor. The computer varies the intensity of light striking each of the three phosphors to produce different colours.
Each phosphor can emit 256 individual values or shades (measured from 0-255). For example, a red phosphor emitting no light (0) will be black, at full intensity (255) it will be white, and all the shades in between (1-254) will be various shades of red. The phosphors are so small that the human eye perceives a phosphor triad (pixel) as a single colour. The number of possible colours that can be generated by the three phosphors in combination can be calculated as follows: 256 x 256 x 256 = 16, 777,216.
For example, by mixing the brightness (or intensity) of the colours like this: 204 Red, 153 Green, and 102 Blue, we produce a tangerine colour (shown). If we were to mix the three colours together at a value of 255 each, it would produce white (all colours on). Red, Green and Blue all set to a value of 0 produce black (all colours off).
Examples of RGB Colours
Here are a few common colour combinations you will see over and over again.
| 0 red |
+ | 0 green |
+ | 0 blue |
= | black | If there is no red, no green, and no blue, that gives us black. |
| 255 red |
+ | 255 green |
+ | 255 blue |
= | white | If there is all red, all green, and all blue, that gives us white. |
| 255 red |
+ | 0 green |
+ | 0 blue |
= | red | If there is all red, no green, and no blue, that gives us red. |
| 0 red |
+ | 255 green |
+ | 0 blue |
= | green | If there is no red, all green, and no blue, that gives us green. |
| 0 red |
+ | 0 green |
+ | 255 blue |
= | blue | If there is no red, no green, and all blue, that gives us blue. |
| 255 red |
+ | 0 green |
+ | 255 blue |
= | magenta | If there is all red, no green, and all blue, that gives us magenta. |
| 255 red |
+ | 255 green |
+ | 0 blue |
= | yellow | If there is all red, all green, and no blue, that gives us yellow. |
| 0 red |
+ | 255 green |
+ | 255 blue |
= | cyan | If there is no red, all green, and all blue, that gives us cyan. |
Colour Space Summary
- A colour model is a way of describing how to define colour. Examples of colour models are RGB and CMYK.
- A colour space defines how a range of colours are defined for a specific device within a colour model.
- Within the RGB colour model, there can exist many different colour spaces; each of which describes colour in the same fashion, but is limited in gamut (range) to a specific device.
- The RGB colour space defines the amount of red, green, and blue that will be used to create a colour. The RGB colour space is used for describing colour for monitors. This is what you will be working with in Photoshop.
- The range of colours that can be reproduced in a specific RGB colour space depends on what device it will be displayed on. This means that the colour space is device-dependent.
- A computer monitor is a grid of tiny points of light called phosphors. Each triad of a red, green and blue phosphor makes up a pixel. By varying the intensity of light emitted by the red, green and blue phosphors, millions of colours can be produced.
Coming Soon:
- Feb 13
- ISSD 24 - XML
- Feb 21
- ISSD 23 - Web 2.0 Technology
- Feb 23
-
Facebook for Business
Hours: 2
Cost: Free!
- Feb 25
-
Search Engine Optimization (SEO)
Hours: 2
Cost: Free!
- Feb 25
-
Search Engine Marketing (SEM)
Hours: 2
Cost: Free!
- Mar 05
- ISSD 23 - Ajax
Photoshop - TOC - Introduction - Books -
Digital Graphics - Links - Questions -
1 - 2 - 3 - 4 - [ 5 ] - 6 - 7 - 8 - 9 - A -
