Photoshop Tutorials - Lab Color Model
Lab Color Model
It would be very useful to determine the standard model that the colors would be brought to at every step of the process, from editing the image to printing it. Lab is one of the successful attempts to create a color model that is based on the human color sensing. Any color in Lab color model is determined by three parameters: Lightness and two chromatic parameters A and B. A is a gradient from green to red, while B is a gradient from blue to yellow.
Brightness setting is separated from the color settings in Lab model. This makes it very useful for regulating the image contrast, sharpness and other tone characteristics of the image. Lab model is three-channel color model. Its color range is extremely wide and is equal to the color range of people. The Lab color model includes the color ranges of all color models within its color range.
Every color channel has its own brightness (luminosity). With same color intensiveness, human eye perceives the green color as the brightest, red color as less bright and blue as the darkest. Please note, that luminosity is the characteristic of perception and not actually the color.
In RGB model, the pixel color tone and brightness are related. For example, saturated blue colors will be very dark while saturated yellow colors will be very bright. All three channels are involved in creating the color of the pixel (point). If all three would be bright then each would contribute one third of the brightness (luminosity):
Y = R/3 + G/3+B/3
This is how HSB color model calculates the brightness (luminosity). But we will talk about it later. As we have found out before, visually different basic colors seem to have different brightness (luminosity) , so HSB model is not actually correct. To determine the actual brightness (luminosity) the following snap formula is used:
Y= 0.2125R+0.7154G + 0,0721В
You can directly view the brightness (luminosity) in the Grayscale model The only channel of such document stores the pixel brightness (luminosity) only without taking color into consideration.