How Converting Images from RGB to CMYK Affects Color

It goes without saying that achieving an accurate color representation of original artwork is the desire of most artists. Artists are inherently DIYers, and their efforts at color correction can lead to hours spent tweaking images, often resulting in frustration and disappointment in the printed results.

If only it were as simple as selecting the option “convert to CMYK” in a photo editing program such as Photoshop. Unfortunately, there is more to it than a mouse click. RGB images tend to darken and dull when converted to CMYK, and some colors are more affected by the conversion than others.

Understanding the Lingo

Before we can understand the challenges of color-matching artwork, we first need to be sure we’re speaking the same language.

DPI or PPI — dots per inch or pixels per inch

These terms are most often used when speaking about the resolution of an image. Most pictures on the internet are displayed at 72 DPI, while images used for color printing need to be at least 300 DPI.

RGB — the colors of light

RGB refers to the three primary colors (red, green, and blue) of light used to create color in TVs, screens, monitors, digital displays, and so on. See how the combination of all three primaries of light results in white, opposite of what we are familiar with. This is why many find it difficult trying to adjust the colors of an RGB image.

Note the mixed hues cyan, magenta, and yellow are lighter in value than the CMYK example below.

CMYK — the colors of print

CMYK is an abbreviation for the four primary colors (cyan, magenta, yellow, and black) of ink used in combination to create a hue in standard printing. Notice how mixing cyan, magenta, and yellow together generates black. As artists, this is the color model most familiar to us.

See how the mixed blue, red, and green hues are darker in value and in the RGB example above.

Below you can see how printed dots of the CMKY inks visually merge creating a color image.

A trick of the trade – magenta or a combination of cyan and magenta dots are often printed along with dots of black (k) ink for a deep, rich-looking color. Look again at the image above, specifically the upper left corner of each color plate. Dots of cyan, magenta, and black inks are included, resulting in a more dynamic black in the full-color composite image on the far right.

6 Steps Toward Better Color

1. RGB is not CMYK

For most artists, adjusting an image on the computer monitor (RGB) until the color looks perfect does not usually result in an accurate color print (CMYK) because the sources of the color primaries are different. The image is displayed in RGB and printed in CMYK.

Glance back at the RGB and CMYK graphics above. Note how the mixed hues in each differ in value from their source/primary colors’ value; these are examples of additive and subtractive color properties. This is one of many contributing factors that add to the difficulty of a straight conversion from RGB to CMYK or vice-versa.

A few other examples of variables to consider while trying to color match original artwork are; having a working knowledge of the equipment, understanding the differences between screen displays and printed results, and the fact that some colors are harder to match in CMYK print, purples for instance.

Did you know that giclée fine art prints are actually printed on a high-end inkjet printer that contains 8–12 different archival inks? Photo Black, Cyan, Vivid Magenta, Yellow, Light Cyan, Vivid Light Magenta, Light Black, Matte Black, Light Light Black, Orange, Green, Violet. This helps explain why giclées are more accurate in color and also why they are more expensive.

2. Apples and Oranges

Screens (monitors) are not created equal, and not all viewing platforms are equivalent. The same image will appear to have subtle color differences when viewed on various screens. In addition, even the same screen will change the way it displays color over time and depending on the amount of use.

You may not be aware that professionals in the field use specialized equipment to calibrate their screen displays and output devices for accurate color every week.

3. Give Yourself a Hand — a color hand

If you really want to get serious about color accuracy – pick up a Color Calibration Chart and include it with all high-resolution photographs and scans of your art. The squares of color on the chart give something for a printer to reference in adjusting an image for accuracy before printing.

In addition to including squares printed with 100% C, M, and Y ink, the chart also includes a value range from white to 100% black. In today’s digital photography age, this value range can help with corrections for white balance. You can read more about the Color Calibration Chart and how it’s used in the article, Meet Your New Friend — the Color Calibration Chart.

Color calibration charts vary widely in price, here is a link to an affordable option available on Amazon.

4. Pixels Matter

Start with the best, highest resolution photo or scan you can get. The resolution or DPI/PPI can always be reduced for various needs, such as a website, but can NEVER be increased.

Think of each pixel as a square of color, with the color squares combining to create a reproduction of your art. When you increase the numeric DPI/PPI of an image in Photoshop, you are basically increasing the number of times that 1 square of color is sliced up into smaller squares. However, the newly created slices will still look like the original square. This is because you are not increasing the detail of an image by increasing the resolution. This will only result in a printed image that looks pixelated.

DO NOT CONVERT A 72 DPI IMAGE TO 300 DPI FOR PRINT!

As a general rule, images for the internet are 72 DPI, and images used for print should be at least 300 DPI. That being said, I always provide the highest resolution file to a printer I can and let them change the resolution to meet their best output.

5. Don’t Scale

I mentioned the importance of DPI or PPI in image resolution; scaling or enlarging an image also reduces the quality of the printed picture. Think about it for a minute. If you enlarge or scale up an image for print, you only make the pixels or squares of color print larger. 

DO NOT ENLARGE AN IMAGE FOR PRINT!

The only time enlarging an image will work — if you start with a much higher resolution, 1600 dpi, for example. This is one reason to always have the photos of your artwork taken at the highest resolution possible. 

6. Make a Sacrifice

Quality, Time, or Cost, which one will you sacrifice? Well, not really sacrifice, but you will need to decide which two of the three are most important to you.

The priorities will change depending on the needs of each printing situation. For instance, if you are printing 200 postcards, time and cost may be the priority. But, if it’s 50 giclée prints, quality will be the most crucial.

Going Forward

Now that you know some of the factors involved in getting a good color representation of your artwork in print, let’s put the knowledge to use.

Quick and Inexpensive

• Online printers such as Vista Print or Overnight Prints are great for quick, low-cost printing. Just keep in mind, the color may not be perfect in the final printed materials. However, there’s nothing wrong with using these printers. I’ve worked with them myself for printing business cards, postcards, and such – but I know that I am giving up a little bit of the color accuracy in trade for a low cost and quick turnaround.
• Looking at a digital proof online will not accurately represent the color in the final printing. You should be checking for placement, spelling, and all the information is included correctly in the layout.

High Quality

• To get the best quality, work with a professional printer. They are worth their expertise and experience.
• Professional printers have color experts on staff who know their systems and adjust an image to get the best color match in printing. Color professionals also work in a specialized environment with color balanced lighting.
• In addition to the high-resolution photography or scan, also include the RAW digital photo file. A RAW digital photo file has minimally processed data from the camera or other sources.
  This may sound really strange, but several years ago, I had trouble with professionally printed images consistently looking too warm. The TIFF photos from my DSLR camera were causing the magenta dot to print a hair larger. The printer was able to correct the issue with the RAW file I provided.   
• Provide the original artwork for the printer to color match. I realize that this may not always be an option. Including the color calibration chart with your art in the original high res photograph or scan will also help printers do their best color matching.

Whew! Who knew there were so many factors to consider.

Honestly, though, this barely scratches the surface of what’s involved in getting the best color reproduction of your original artwork; there is dot gain, file types, image compression, paper surfaces, and so on. 

No wonder you’ve ended up frustrated after spending all that time at the computer adjusting colors, and why it’s not as easy as selecting “convert to CMYK” in Photoshop.

Other Helpful Resources:

– Get the Best High-Res Images of Your Artwork
– Quick Steps to Photograph your Art with a Cellphone — if it’s your only option!
– Meet Your New Friend — the Color Calibration Chart
– Color Calibration Chart on Amazon

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