Images that are viewed on a computer monitor will never have the exact same colors as what will come out of your printer (or your neighbor's printer, for that matter). The reason for this is not only that every monitor is different, but color created from light (your monitor) looks different from color created from ink (your printer). On top of that, your camera, scanner, monitor, and printer all talk different color languages and use different ink formulas. None of them map the same actual color to the same values. This is why designers frequently remind clients that color matching of the materials they are viewing may be imprecise.
The two basic categories of color that are most often used in graphic production are:
• RGB: Red, Green, Blue - The colors used on computer
monitors, digital cameras, televisions, and other light-based devices. This
is a color system based on combining light to produce color. The more
light you add, the lighter the image becomes. This is called additive color.
• CMYK: Cyan, Magenta, Yellow, Black - This is the standard color mode for printing projects. This is an process that is based on combining pigments in varying amount to produce color. The more ink (pigment) you add, the darker the image becomes. This is called subtractive color.
One of the most important concepts for understanding color models is the idea of color gamut. The entire range of the color spectrum is extremely broad, extending beyond the range of human visual perception, from infrared to ultraviolet. There are millions of colors that can exist in this range. However, not all of these colors can actually be created or displayed by devices such as computer monitors and printing presses. These devices are only capable of using a limited subset of the full spectrum and each generally uses a different subset. Color gamut is the range of color that can actually exist within any color model, for any particular device. Subsets of the overall color spectrum are also sometimes referred to as a color space.
The problem frequently becomes one of moving an image through a production workflow where every device has a slightly different color gamut. Imagine scanning into one color space, then editing the image on your computer monitor in another color space, sending it to a client who has a different brand of monitor with it's own color space, printing to a desktop color printer with another color space, and then finally outputting to film for offset press in yet another color space.
Although there may be large areas of the gamut that overlap between devices, there are also areas that do not. The classic example of this is the difference between pigment-based colors used in printing and light-based colors used in computer monitors.
These are also called additive and subtractive color.
Monitor colors are additive since, in order to make a color get closer to white, more light has to be added; but, when trying the same effect for printed colors, it is necessary to subtract pigment, then these are called subtractive colors.
Additive colors are produced by light emission (when an eye sees the light
directly generated from a light source) and subtractive colors are produced
by light absorption (the eye sees the light that was not absorbed but reflected
by the colored surface).
Or from another point of view: color absence in a monitor produces black, so light must be added to show color. Color absence on a sheet of paper produces white, then light must be subtracted by pigments to produce color.
Due to radical differences between these color spaces, it is very easy to create colors on your monitor that cannot be reproduced in print. This is one reason why you should never completely trust what you see on screen as a reliable indicator of how it will print.
This is also why designers frequently remind clients that color matching of the materials they are viewing may be imprecise.
RGB (Red-Green-Blue) are colors used on computer monitors, digital cameras, televisions, and other light-based devices. This is a color system based on combining light to produce color. The more light you add, the lighter the image becomes.
RGB has the broadest color gamut. But even within RGB there are variations that each have different color gamut. Image editing applications such as Photoshop allow you to select among these to optimize your results. The main one is Adobe sRGB. It has an extremely broad gamut and can produce millions of colors using various formulas.
For instance, the RGB color formula for United Way Blue is:
R=16%, G=22% and B=127% or 16-22-127
For United Way Red the formula is:
R=254%, G=35% and B=10% or 254-45-10
The formula for white has all three values of 255.
The formula for black has all three values of 0.
One of the common color tables is called the "web-safe" palette. Both PCs and Macs allow 256 colors in their operating system. This is a common display setting for monitors. However, there are only 216 colors that match between the two systems. The web-safe palette indexes images to these common colors so that colors will be more consistent across platforms. These web-safe colors also have reference codes referred to as hexadecimal numbers.
For instance, the Indexed color number for United Way Blue is #0056A7
For United Way Red the formula is # F04E31
The formula for white is #FFFFFF.
The formula for black is #000000.
Since most computer monitors these days are capable of showing millions of colors, the only real call for using "web-safe" colors these days is when you want to further reduce file size. With only 216 colors (or even fewer) embedded into the image file, this is a great way to have images download quickly. This file format is not recommended for photographs.
CMYK: Cyan, Magenta, Yellow, Black - Also known as "process color." This is the standard color mode for printing projects. This is a process that is based on combining ink pigments in varying amount to produce color. The more pigment you add the darker the image becomes.
The four standard colors that every printing press uses are: Cyan (C), Magenta (M), Yellow (Y) and Black (K). The standardization has become known as the process — thus process color. Specific colors in this system are always cited as percentages of the four component parts in the C-M-Y-K order.
For instance, the process color formula for United Way Blue is:
C=100%, M=74%, Y=0% and K=0% or 100-74-0-0
For United Way Red the formula is:
C=10%, M=85%, Y=89% and K=0% or 10-85-89-0
The formula for white has all four values of 0%.
Black has all values of 0% except K, which is 100%.
Process color is the standard color mode for printing production. Everything from low-end desktop ink jet printers to high-end offset presses the size of a Greyhound bus use this system to create full-color reproduction. CMYK is generally always the best color destination space for printed projects.
Because CMYK is so limited in its color range, some presses have the ability to add custom green and orange inks, colors that CMYK does not produce particularly well.
There are numerous ways to configure CMYK files for different printing methods. However, with process color the differences are less about gamut and more about the mechanics of printing. The key to achieving the best reproduction within this space is making sure that the attributes of your file are set up to accommodate these differences. These include technical considerations such as how much ink the paper will soak up. Taking control of, and responsibility for these can be complex.
As noted previously, RGB files will usually print on CMYK color devices (not professional printing presses), but there is always a color conversion performed by the device, and this conversion may not be an accurate one. It is generally better to do your own conversion and take control of the details.
When color is absolutely crucial, there is also a set of pre-blended inks called PANTONE. As you can see from the gamut chart above, the Pantone gamut is larger than the CMYK gamut. The main strength of Pantone’s color profile is for spot colors, such as large areas of solid color and publications which require very few colors. However when it comes to printing more complex images, like photographs, there are limitations in the ability of the profile and the process becomes expensive.
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