Images are known as “True Color” images when each pixel is defined in terms of its actual RGB (Red ,Green, Blue) or CMYK(Cyan,Magenta,Yellow,blacK) values. Every pixel in a true color image has 256 possible values for each of it’s red, green or blue components (in the RGB model) or cyan, magenta, yellow and black (in the CMYK model).Because there are 256 possible values for each RGB or CMYK component, then RGB true color would have a 24-bit color depth each colour being 8 bit long and accordingly CMYK true color would have a 32-bit color depth. There are millions of possible colors for each pixel in a true color image. That’s why it is called “True Color”.
RGB images are derived from the three primary colors of red, green and blue. In 24-bit RGB color, each red, green and blue component is 8 bits long and has 256 variations in intensity. These variations are represented in a scale of values ranging from 0 to 255 with 0 having the least intensity and 255 having the greatest. When the 3 components are combined there are 256 x 256 x 256 possible combinations or 16,777,216 possible colors.
For example, white would be composed of maximum intensity of red, green and blue light (R=255 G=255 B=255) and black would be composed of zero intensity of red, green and blue light (R=0 G=0 B=0). Cyan would be composed of maximum intensity of blue and green light and zero intensity of red light (R=0 B=255 G=255). Magenta would be composed of maximum intensity of red and blue light and zero intensity of green light (R=255 G=0 B=255).
Human eye perceives the true colours in the following way –
The eye contains two kinds of receptors through which an individual is able to see different colours are namely rods and cones. While the rods convey shades of gray, the cones allow the brain to perceive color hues. There are three types of cones. Of the three types of cones, the first is sensitive to red-orange light, the second to green light and the third to blue-violet light. When a single cone is stimulated, the brain perceives the corresponding color.
That is, if our green cones are stimulated, we see “green”. Or if our red-orange cones are stimulated, we see “red”. If both our green and red-orange cones are simultaneously stimulated, our perception is yellow. Thus in this manner human eye sees all colour with the simulation of different cones which forms the required colours.
The advantage of true colour over a conventional palette based colours is that it does not restrict the range of colours which can be displayed on screen simultaneously. For example, if eight bits are used to store each component of each pixel then a total of 2 raise to 24 (about 16 million) different colours can be displayed at once which would require a very expensive palette with 3 * 2 raise to 24 which would take more amountof memory then true colour will take.
Images using the CMYK color model are also true color. CMYK images are derived from the primary colors like cyan, magenta and yellow and black. In 32-bit CMYK color, each cyan, magenta, yellow and black component is also 8 bits long and has 256 variations in intensity. Each pixel in a 32-bit CMYK image is one of 256 x 256 x 256 x 256 variations possible colors.
A mix of 100% each of cyan, magenta and yellow produces black. Many graphics programs support both color models meaning RGB and CMYK. When one comes across true colour,Colour Depth is also a terminology which needs to be known.
Colour Depth – Each pixel of a screen image is displayed using a combination of three different colour signals namely red, green and blue. The precise appearance of each pixel is controlled by the intensity of these three beams of light and the amount of information that is stored in a pixel determines its colour depth. The more bits that are used per pixel (“bit depth”), the finer the colour detail of the image.
Color depth is a computer graphics term describing the number of bits used to represent the color of a single pixel in an image. This concept is also known as bits per pixel (bpp). Higher color depth gives a broader range of distinct colors.
Graphics with lower color depths do not require as much frame buffer memory or display bandwidth, allowing them to be generated and displayed more quickly. Increasing color depth results in higher color quality at the expense of display speed and responsiveness.