The Difference between CMYK and RGB Color Models

estimated reading time: 7 minutes

First of all, what is a Color Model?

A Color Model refers to a system for creating a range of colors from a small set of base colors. Your first introduction to this concept was probably in kindergarten when you learned about the RBY color model, which is based on the primary colors of Red, Blue, and Yellow.

Even at 5 years old, it was easy to understand that mixing Red and Blue created purple, mixing Red and Yellow created Orange, and mixing Blue and Yellow created Green. Viola! You now had the traditional range of colors from which to create fingerpaint masterpieces.

Though we might not have realized it, by the time many of us learned about RBY in kindergarten we had already been regularly engaging with media created by two other important color models - RGB and CMYK.

What is the RGB color model?

The primary colors of the RGB color model are Red, Green, and Blue. These are the colors that correspond to the three types of cone cells in our retinas that detect different wavelengths of light.

Long wavelengths of light are interpreted by our brains as being the color red, medium wavelengths of light are interpreted as the color green, and short wavelengths of light are interpreted as the color blue.

A huge gamut of colors can be created by combining red, green, and blue light in various combinations of intensity. In turn, these different colors of the spectrum are perceived by the brain based on the mix of long (red), medium (green), and short (blue) wavelengths they contain.

Because the RGB color model is used in light-based systems, it is the reason we are able to view colorful images and videos on the screens of electronic devices, such as computers, tablets, and cell phones. Anything intended to be viewed online, such as graphics for digital marketing, web pages, or social media profiles, must use the RGB color model.

RGB: Pixels and Sub-Pixels

When computers and cell phones are off, their screens are dark. When these devices are powered on, the screen becomes illuminated with thousands of tiny boxes of light called pixels.

A "pixel" (short for picture element) is the smallest component of any digitally-displayed content. Arranged in a grid formation, pixels are the fundamental building blocks of digital images.

Within each pixel are three different types of sub-pixels. Each sub-pixel is able to emit a wavelength of light. One kind of sub-pixel emits a long wavelength of light (red), another sub-pixel emits a medium wavelength of light (green), and the third emits a short wavelength of light (blue).

If you refer to the magnified photo of the blue eye, you will see an extreme close-up of the sub-pixels on a computer screen showing as red, green, and blue.

On an electronic device, the three colors of RGB can be displayed in intensities from 0 to 255. For example, if the red sub-pixel is set to its maximum value of 255 and the green and blue sub-pixels are both turned off (255, 0, 0) the entire pixel will show as pure red. Likewise, a setting of 0, 255, 0 will produce a pure Green pixel and a setting of 0, 0, 255 will produce a pure Blue pixel.

Of course, changing the intensity of the three light colors to any value within the range of 0 and 255 will produce thousands upon thousands of other pixel colors. For example, Cyan can be created by setting Blue and Green to full value and turning off Red (0, 255, 255).

Likewise, Magenta can be created by setting Red and Blue to full value and turning off Green (255, 0, 255) and Yellow can be created by setting Red and Green to full value and turning off Blue (255, 255, 0).

When Red, Green, and Blue are all set to their maximum value (255, 255, 255), this yields the color white.

Having different colored pixels, all bumped up against each other, is what forms the vibrantly colored images we see on our computer monitors, cell phone screens, and other digital displays.

Also, by increasing the intensity of the light we add to the pixels, the brighter and richer images will become. This is why RGB is known as an "additive color model", because we are adding different light from the spectrum together to attain other visible colors.

What is the CMYK color model?

Unlike a computer monitor or cell phone screen, a piece of paper cannot generate its own light source. Instead, paper must rely on reflected light.

Hence, the pigments and inks used to create printed materials such as books, brochures, magazines, postcards, and posters do not use the RGB color model.

Instead, the printing industry uses the CMYK color model. The primary colors of the CMYK color model are Cyan, Magenta, and Yellow. Black (K) is also included in this color model to provide depth and contrast.

The printing process starts off with sheets of blank paper. Prior to receiving any ink or toner pigments, the blank paper reflects all wavelengths of light equally. Since white is the sum of all visible colors of light, our brain perceives the paper to be white.

Though electronic devices can add different wavelengths of light to create colors, a sheet of paper has no light source of its own. As such, the toner or ink used in the CMYK color model is applied to the paper sheet to absorb various wavelengths of light reflecting off of it.

This subtracts out certain colors of the spectrum so that only the desired colors reflect off the sheet into our eyes. As such, CMYK is known as a "subtractive color model" because it starts with white light and then subtracts out portions of it to achieve various other colors.

CMYK: Dots instead of Pixels

As the paper, cardstock, or other substrate moves through a printing press, the four CMYK colors - Cyan, Magenta, Yellow, and Black - are applied one after the other. The order of when black is applied can sometimes change but the CMY colors are almost always applied in the same order.

Each of the four CMYK colors can have an intensity value of 0% to 100%. These percentages are used to indicate the amount of each ink color is needed to build a particular color when printing. A value of 0% for all four CMYK colors represents white (the underlying sheet) while a value of 100% for all components creates the deepest black.

The printing press applies each layer of color as tiny dots of ink (or toner). See magnified photo of brown eye. These dots are applied in successive layers, overlapping portions of the white paper but also overlapping some of the other ink dots that have been applied.

Just as the RGB color model merges various intensities of Red, Green, or Blue light to induce the brain to perceive thousands of other colors, the size, intensity, and relative placement of the Cyan, Magenta, Yellow and Black dots on the printed sheet also tricks the brain into perceiving thousands of different colors.

Whereas RGB colors will get brighter as more light is added, CMYK colors will get darker as more ink or toner is applied. Also, when we look at something that has been printed with the CMYK process, we see colors that are solid and continuous. We can only see the individual dots if we view the printing under heavy magnification.

The subtractive color model of CMYK cannot produce as many colors as the additive color model of RGB, nor can it achieve as many bright colors. However, CMYK results in very eye-pleasing color for print materials. As such, CMYK is the printing industry standard for creating full-color printing.

RGB for Digital Content, CMYK for Printed Content

The main takeaway from this article is that the RGB and CMYK color models operate on different principles. These two systems are not interchangeable.

The RGB color model is used when creating media that will be presented in digital form - such as websites, banner ads, and other digital communications that will display on a computer, cell phone, or other electronic devices. The CMYK color model is used when creating materials that will be printed - such as books, brochures, flyers, magazines, posters, and postcards.

Hence, any image files being created for display on an electronic device must use RGB colors and any image files created for printed output must be set up in CMYK.

It is important to note that any images submitted for printing in RGB mode will be converted to CMYK prior to printing, which may yield a result you weren't expecting. If in doubt, check with your printer beforehand about their preferred file settings and/or consider getting a hard copy proof for any color sensitive projects.

Color Vision is always ready to help!

If you have any questions about CMYK vs RGB or any other print-related topics, get in touch with Color Vision Printing.

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