RGB
In Photoshop we use the RGB color group which is made up of Red, Green and Blue. These colors make up the three color channels in RGB and are known as the additive primaries. When all three emitted colors are added together, they create white light. When the traditional primary colors, red, yellow and blue are added together they create black (although it’s more of an unappealing brown). The difference is because additive primaries ARE light – they emit light. Instead of emitting light, the traditional primaries reflect and absorb light. Since computer screens emit light, RGB should always be used for viewing work on screens.
The RGB colors get broken down into numbers in order to be interpreted and then subsequently displayed correctly by browsers. The scale that the numbers can range from goes from 0-255, with 0 being the absence of that color and 255 being 100% of that color. The numbers are then further translated into six digit hexidecimal numbers (triplets). Different browsers interpret information differently however and this problem also extends to the interpretation of colors, so one must be careful to ensure that their colors are browser safe.
CMYK
For images that will be printed the CMYK color group is used. C=cyan, M=magenta, Y=yellow. Black (K) is also used. These colors make up the four color channels of CMYK. They are called the subtractive primaries because when one subtracts a color out of the additive primaries, one of those colors is left. Subtract red from the group and one is left with cyan, subtract blue and one is left with yellow and subtract green to end up with magenta. These colors are not blended together when something is printed. Instead, millions of tiny dots of these colors are grouped next to each other, in order to achieve the desired color. A group of cyan and black dots would mix and appear as a dark blue color to our eye.
GRAYSCALE
The grayscale option in photoshop uses up to 256 shades of grey, so unlike RGB and CMYK, it only contains one channel. If one wants to create a black and white image, you can just convert it to grayscale. Grayscale destroys all the color information though, so you should always make a copy in order to retain all the original information.
LAB COLOR
The lab color mode contains all the colors that are used in RGB and in CMYK. It contains three channels: the lightness channel (L), channel a and channel b. The L channel controls how dark or light an image is. A lightness value of 100 would make the image white, whereas one of 0 would make the image black. The other two channels, a and b, control colors. The a channel controls the color ranges from green to red. The b channel controls the color ranges from blue to yellow. Unlike RGB or CYMK, the lab color mode is device independent, so the color will always remain consistent.
HUES, TINTS AND SHADES
A color, like red, is called a hue. When the hue is pure it is fully saturated. To change the saturation of a hue, one can add a tint or shade to it. The addition of white to a color would make it a lighter tint, whereas the addition of black would make it a darker shade. Tints and shades come in handy when one wants to play around with contrast. Black and white is the most extreme contrast, so if one wanted to experiment with this, they could create contrast by adding white to a hue and placing this hue next to one that has had black added to it.
Of course, using complimentary colors, like green next to red, blue next to orange etc will also create contrast. However, when these colors are placed next to each other they start to vibrate, which can be very tiring on the eyes. It really just depends what you want to accomplish and what effect you want to have on the viewer.
