Ask a Smartpress.com Expert: Converting RGB to CMYK

by Jill Alfano | July 1, 2013

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I didn’t realize I made my design file in RGB, I think my digital printing results will be better with the CMYK color model. When I converted it, the colors didn’t look right. How can I fix the colors in my graphic design file when converting it from RGB to CMYK?

– Enraged by RGB

Smartpress tutorial - RGB image

RGB Original File

I feel for you. Anyone who has ever converted an RGB image to CMYK knows how frustrating results can be. The beautiful image you worked so hard on is a shadow of what it used to be – literally, because the most notable difference is going to be reduced color saturation.

Smartpress tutorial - RGB to CMKY

CMYK Converted File

To optimize most files for our printing process the SmartPress proofing process will automatically convert your files to GRACoL 2006 CMYK (Our press color space), via a combination of perceptual and colormetric rendering intents. Now, although we try to provide the best conversion possible with no sacrifice of color accuracy and detail, there is no such thing as a one size fits all conversion. If you like the way your proof looks, please accept it and continue on with your order knowing that it will print out reasonably close to what you have seen on screen.

If it doesn’t look quite right, you can convert the file to CMYK, but you may lose some of the detail and the contrast in your image. The problem with such a conversion is that the range of colors – referred to as gamut – produced using CMYK color inks on paper is different than what can be represented using RGB. This where the changed color hues and a dull appearance originate. Thankfully, there are ways to restore the colors that are lost in your RGB to CMYK conversion.

First, some instructions on converting your images from RGB to CMYK in Photoshop.

  1. Make any adjustments or edits to your image, including applying filters, while the image is still in the RGB color space. Save and close the file.
  2. Select “Edit” then “Color Setting.”
  3. At the dropdown list under “Settings” you will see presets for Europe, North America and Japan. Select the appropriate location.
  4. Next, select a CMYK profile that best suits the final printing conditions. For example, “GRACoL 2006” is our default color management profile at Smartpress.com.
  5. Click on the “More Options” button. This will let you select the rendering intent, Color Engine and black point compensation. Here is where you are going to get the most variation and control of your conversion.
    Perceptual rendering intent will preserve smooth transitions and gradients, this is great for people with lots of shadows, or sunsets or skies.
    Relative Colormetric provides the greatest color accuracy but can do so at the expense of shadow detail or smooth gradients and transitions. Selecting Black Point compensation can give some shadow detail back at the expense of saturation.
    Saturation rendering intent will provide the most vivid colors but often does so at the cost of a natural realistic look.
  6. Once you have the best color settings, you can open the RGB image you want to convert.
  7. A photograph from a digital camera will probably have an embedded RGB color profile. If Photoshop presents a window with “Embedded Profile Mismatch” then select “Use the embedded profile.” If Photoshop presents a message that says the image does not have an embedded RGB profile, choosing to “Assign profile” to sRGB is a good option.
    RGM CMYK Gamut Warning

    The Gamut Warning will show in gray which colors won’t convert cleanly.

  8. To see which areas of the image that are “Out of gamut”, select “View” and then “Gamut Warning.” Any colors that turn grey are colors that can not be produced in the CMYK color space and Photoshop will have to select the nearest color to it, depending on the rendering intent you selected earlier.
  9. To covert from RGB to CMYK, select “Image,” then “Mode,” then “CMYK Color.”

Once you’ve made the conversion, you will probably notice that some of the colors changed and have almost a faded look. Here is one way to try to restore the color, though there may be other methods that might work better with your particular image:

  1. Add a new layer in Photoshop.
  2. Fill it with black.
  3. Set the color mode of the layer to Color Burn.
  4. Adjust the layer opacity until you’re happy, usually in the 15-35% range.
  5. You can also add a Hue/Saturation adjustment layer. Find a balance between the saturation adjustment layer and the color burn layer to get your CMYK conversion as close to the RGB original as possible.

Ideally, your best bet is to create the images for your digital printing project in the CMYK space in the first place because RGB suffers a loss of color when it is converted. You can use the above to get as close as possible to appearance you’d like your image to have.

Have a question about online printing that you would like to have answered? Leave your question in the comments below or email us at customerservice@smartpress.com and we will do our best to answer your questions.

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