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RGB vs. CMYK

Every industry has its own special jargon – acronyms and specialized words to describe common functions, items and procedures. It can be daunting to understand the conversation of people as they use work-speak, especially if you haven’t had time to master the “language”. The visual and digital communications industry has its own special language as well.

When speaking about color printing and display you may hear several acronyms that could be confusing. We wish to address a few of these terms to help reduce the confusion.

 

THE STRATEGY

The reason for this discussion is to review a commonly confused design function that can result in additional costs being added to your bill for correcting artwork. It is important that your images and other color items be in the proper mode for the output you desire (print/digital use). By understanding the following descriptions and correctly applying the knowledge presented, you can better prepare your files for output and achieve your expected results from your print provider without needing additional attention to your file or experiencing a delay in production.

 

THE DETAILS

RGB vs. CMYK-1

RGB – The Digital Color Model

Colors are rendered in many ways. On a monitor, projector, or any other digital format such as the Web, we refer to the RGB (Red, Green, and Blue) mechanism for rendering color. “RGB” refers to the three colors of pixels used on screens. Colors are created on the display when a Red, Green or Blue element is stimulated with an electrical charge. The varying amounts of charge to these screen elements cause them to glow. By combining these three colors, the desired hue is created to in order to form a picture.

White is a combination of all the colors, while black is the lack of color/light. Grab a magnifying glass and check this out on your television or computer screen. If you get up close to a jumbotron, the whole concept becomes obvious.

 

RGB vs. CMYK-2

CMYK – The Print Color Model

The CMYK color model (also known as the “Process” color model) uses inks or toners in the digital color press to print on white paper. The colors used in the CMYK/Process model for printing are Cyan (light blue), Magenta (a pinkish red), Yellow, and Black (K), referred to as “CMYK”. With various combinations of different amounts of the four ink or toner colors, a large range of color hues can result.

 

Working Between RGB and CMYK

It is necessary to understand that some color ranges in CMYK will appear significantly different than what you see on the monitor. The reason is that RGB colors on the monitor do not always translate equally into the CMYK mode. Thus it is not always possible to exactly match colors seen on the screen to colors you want to print on paper.

If you send a printer RGB images they must be converted to CMYK mode in order to print them with a CMYK set of inks or toners. There are no printing devices that print in RGB colors. Ironically, if you wish to view a CMYK image on a monitor, it has to be converted to RGB color space to be properly viewed.

When a printing device converts RGB to CMYK, colors change and generally do not represent the original file colors. Therefore, in order to get an acceptable printing result, any RGB-mode images or colors must be converted using a color management software such as Adobe Photoshop. If you don’t do that before sending your files to your printer, the printer must make the change, which sometimes results in an unintended color shift.

 

RGB vs. CMYK-3

Pantone/Spot Colors

Pantone (or “spot”) colors are based on ink colors for offset printing and don’t closely relate to either the RGB or CMYK color spaces. It is a convenient color gauge, as many people in the graphic industry have access to a Pantone swatch book. However, one must remember that in order to produce the colors in this system, the chosen ink color has to be printed on a printing press. Although you can find charts on the internet for converting Pantone to RGB and CMYK color spaces, many Pantone colors can not be matched at all in the CMYK or RGB spaces and others, where conversion numbers are available, look very different when compared to the Pantone color. Pantone color swatches, though convenient, do not relate to digital color spaces and shouldn’t be relied on as such.

In today’s digital world, when creating logos and company brand guides, it would be wise to base specifications on both offset printing (Pantone and CMYK) criteria and digital printing/internet usage criteria, since virtually all small run printing or communications will be digital.

 

THE TAKE-AWAY

Before beginning your layout and design efforts, be certain that all your images and colors are in the color mode necessary for the type of project you have. If the job is being prepared for print, change everything to CMYK. If the final product will only be viewed on a monitor, ensure that your design is in RGB. Don’t assume the mode is correct unless it comes from a previously categorized folder of known files. Also, don’t assume that color images will translate well into a grayscale image for printing. In a grayscale conversion, it will be necessary to introduce more contrast and perhaps more brightness to achieve an appropriate black and white image with proper contrast.

There may be other color adjustments necessary to correct images taken indoors with fluorescent or incandescent lighting. Fluorescent lights may give off a greenish cast to your image and incandescent lights can make everything look orange. Simple color adjustments in Adobe Photoshop or other color management software will add a professional look to uncorrected images. Photo correction will be a future topic for the blog.

The bottom line with color is that everything in your print file has to be in the same color mode, whether it be used in the printing or viewing process. If any one element is different from the rest, it may disappear in the rendering process or potentially change colors when converted.

Other info and References
Additive/Subtractive Color Spaces
The total number of discreet colors, by combining shades of RGB, that can be displayed on a monitor is very large – 16,777,216 colors to be exact. This color model is said to be an “additive” process because by starting with black (no light) you gradually add various intensities of each of the three colors (RGB) to render the various hues. When you get to white, you have added 100% of each color.

The CMYK color model is classified as a “subtractive” model because when moving from Black (which one may assume is 100% of all the colors) to white, ink colors have to be reduced or subtracted to 0% to get to white, which is the underlying color of the paper.

Regarding Digital Devices (Cameras, Scanners, and Phones)
All standard cameras and scanners create their images using an RGB color space. The chip behind the lens that captures the picture, called a CCD (Charge-coupled device), actually has three layers of sensing screens – one for each of the three colors in the RGB color space. Phones, cameras, scanners, etc., have various sizes and qualities of CCD’s containing different numbers of pixels. A 10 MegaPixel camera uses a CCD with 10 million light-sensing cells. The more cells on a CCD, the finer the resolution of the images being produced by the device.

Additional Color Modes
To complicate things even further, other color models or modes that you may run across, in addition to CMYK, RGB and Pantone include Greyscale, Duotone, Hex (Hexadecimal), Lab, Bitmap, Index and Multichannel.

Multichannel systems are used in various digital printers to expand the capability of the printer’s gamut (or range of possible colors). Because digital printers have difficulty rendering lighter shades of color, many inkjet printers commonly use CMYK and lightC and lightM to improve printing of the lighter colors rather than trying to reduce the C and M to very low levels. Another interesting Multichannel system is CMYK plus Green, Orange, Purple, or Red. This combination of CMYK and spot colors improves the printer’s ability to render colors that are difficult for the CMYK system to produce or that lie outside the normal CMYK gamut.

 

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