Lab color space

Compared with RGB color space, Lab is an uncommon color space. It is a device-independent color system and a color system based on physiological characteristics. This means that it describes visual perception in a digital way. The L component in the Lab color space is used to represent the Brightness of the pixel, and its value range is [0,100], representing from pure black to pure white. A represents the range from red to green, and the value range is [127,-128]; B represents the range from yellow to blue, and the value range is [127,-128].

Differences between the two:

RGB is composed of red channel (R), green channel (G) and blue channel (B). The brightest red + the brightest green + the brightest blue = white. The darkest red + the darkest green + the darkest blue = black; And between the lightest and the darkest, red with the same shade + green with the same shade + blue with the same shade = gray. In any RGB channel, white and black represent the intensity of the color. Therefore, where there is white or grey, the R, G and B channels cannot be black, because there must be R, G and B channels to make up these colors.

LAB is not the same, LAB brightness channel (L) is specifically responsible for the brightness of the entire picture, simply said is the black and white version of the entire picture. Channel A and Channel B are only responsible for the number of colors. Channel A represents the range from magenta (white in the channel) to dark green (black in the channel); B is the range from charred yellow (white in the channel) to blue (black in the channel); 50% neutral gray in channels A and B means no color, so the closer the gray is, the less color it is. Moreover, the colors of channels A and B have no brightness. This explains why the outline of the red T-shirt is so clear in channel A and B! Because red is magenta plus caramel yellow.

In summary:

1. Most LAB patterns suitable for RGB channel cut-out can be completed, otherwise, they are not valid.

2. In any single tone background, the part with obvious color difference can be cut out with the channel, and the LAB mode can be quickly completed

3. Any operation (such as sharpening, blurring, etc.) on the brightness (L) channel in LAB mode will not affect the hue.