Week 3 (Part 6: Understanding Color)
The basics of colour
How we see color
How do we see colors? Well, let's visit my color site and find out. Click this link to learn more.
Additive vs. Subtractive color
Find explanations of both here:
Additive Color
Subtractive Color
Color reproduction in print/film
Lets visit this site one more time.
Color reproduction in print
RGB
The RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue.
The main purpose of the RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography. Before the electronic age, the RGB color model already had a solid theory behind it, based in human perception of colors.
RGB is a device-dependent color space: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same color across devices without some kind of color management.
Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras. Typical RGB output devices are TV sets of various technologies (CRT, LCD, plasma, etc.), computer and mobile phone displays, video projectors, multicolor LED displays, and large screens as JumboTron, etc. Color printers, on the other hand, are not RGB devices, but subtractive color devices (typically CMYK color model) which we will cover next.
CMYK
The CMYK color model, often referred to as process color or four color, is a subtractive color model, used in color printing, also used to describe the printing process itself. CMYK refers to the four inks used in most color printing: cyan, magenta, yellow, and key (black). Though it varies by print house, press operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.
The “K” in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Some sources suggest that the “K” in CMYK comes from the last letter in "black" and was chosen because B already means blue. However, such explanations are likely inaccurate, plausible inventions of authors unfamiliar with traditional printing technology.
The CMYK model works by partially or entirely masking certain colors on the typically white background (that is, absorbing particular wavelengths of light). Such a model is called subtractive because inks “subtract” brightness from white.
In additive color models such as RGB, white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is just the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by substituting black ink for the combination of cyan, magenta and yellow.
Out of Gamut
Because the two color spaces (eg. RGB and CMYK) are capable of encompassing a slightly different range of colors, What happens to these colors if your image contains some of these colors and you convert from one space to another? Basically, these colors become altered to the closest facsimile in most cases. There are variations on how these colors are handled, but for the scope of this course, let's just be aware that these are known as "Out of Gamut Colors" and need to be "re-mapped" going from one space to another.