From varying combinations of Red Green and Blue (RGB) we can make any color from the visible light spectrum. In the same way, the range of colors we find in an image are made up of varying amounts of R G and B. Digital camera’s sensor’s employ a grid of light buckets that collect light, measure amounts of light and translate these into a series of numbers that define tones from black to white and color amounts of RGB. In a typical digital color image there are 3 color channels-R G and B. The colors and tones you find in an image are calculated by the numbers generated from the light captured by the camera’s sensor.
In a color picture, any point in an image has a brightness value somewhere between 0 – 255 for each of the colors Red, Blue and Green. A color is defined, described and identified by these numbers. In Photoshop this information is stored in channels, one each for R G and B. You can see a histogram for each of these channels by opening an image and then opening up the histogram display by going to menu-window/histogram. You will see a graphical display of the tones of the image, same as when you open the levels adjustment tool. To see a histogram for each color, click on the pull down menu in the upper right corner of the histogram window. Select all channels view and show channels in color.
If we view an image through Photoshop, we can read the varying amounts of RGB at any point on an image with the eye dropper and the info pallet. Open an image and bring up the info pallet: menu bar–> window/info . By moving the curser over any part of the image you’ll get a reading of how much red blue or green is at any given point. If RG and B, all 3, read 0, then you have a point that is pure black, no other colors, no detail. If you put your curser over a point in an image and you get 255 for each of RGB then you have a point of pure white, no other color and no detail. Normally a point will be some varying combination of numbers for RG and B. If you have the curser over a green area, you will see the green numbers higher than red and blue, etc. If you have a very saturated blue, the number for blue will be vary high and the others low.
Color has 3 variables: hue, saturation and value (Value is also called lightness, luminance and brightness). Hue is the dominant wave length of reflected light, RG and B are 3 different hues. Saturation (aka chroma) is a measure of a color’s, intensity,strength and purity. For example a more saturated red will be very Red, and will appear more pronounced with more pop than a less saturated red. Value is also known as brightness, lightness, and luminence. Value is how light or dark a given color is. Painters control value by adding white or black paint to a color to make it lighter or darker.
Photoshop gives us tools to control colors through manipulating hue, saturation and value. My favorite tool is the Hue Saturation Value ( PS calls value Lightness) which gives us enormous control of color. This tool can be found on the bottom of the layers pallet in the layer adjustment button or on the menu bar under image/adjustments/hue saturation…. You’ll notice when you open it, the opening window gives us global adjustments for each of H S L, if you click on the pull down menu you’ll get the same options for each individual color.
Primary colors combine to produce all the colors we perceive. there are 2 groups:
1-additive colors are Red Blue and Green = RGB
2-subtractive colors are Cyan Magenta Yellow = CMY
Computer Screens emit light and work with RGB colors. When we work in Photoshop we are working in RGB color. Digital files are RGB and files sent to an inkjet printer need to be in RGB.
CMY is used for all printed images, postcard, poster, prints, books. Inkjet printers are set up to receive RGB files and then translates those files to CMY (aka cmyk, the K is for black).