How to use Photoshop's Gamut warning

Gamut = Colours that are within the colour space you are using
Out of Gamut = Colours that fall outside the colour space you are using

Have you ever created a design in Photoshop and had it printed only to be left wondering where your colours went? Did the printer guy put a can of vaseline over your artwork, did they forget to add ink, what on earth happened...? Often the answer is that the missing or dulled colours in the printed version were out of Gamut.

Colour Profiles

RGB = Red Green Blue (additive colour mixing)

Varying intensity of 3 components (beams of red green and blue light) are used to create the colours within the RGB colour profile. To illustrate this simply: Zero intensity from each of the 3 colour components will produce black (which has the RGB value of: (R) 0, (G) 0, (B), 0) whereas maximum intensity from each of the 3 colour components will produce white (which has the RGB value of: (R) 255, (G) 255, (B), 255). RGB is the colour profile used on computer screens and televisions. If you mainly design for on screen applications, you may never come across the out of gamut issue, but if you want to print your artwork it helps to know a little more about how colour profiles work.


CMYK = Cyan Magenta Yellow Key (Black) (subtractive colour mixing)

CMYK is the colour profile used in colour printing. The CMYK colour profile is made up by partially or entirely masking colours on a lighter background (white paper or canvas). The ink reduces the light that would otherwise be reflected - subtracting brightness from white; hence it is referred to as a subtractive colour mixing model.

Comparing Visible (to the eye), RGB and CMYK colour spectrum 

(image source: mosaic design service) 

Comparing RGB colour profile to CMYK

(image source: Wikipedia)

As you can see in the images above, the RGB spectrum is both larger and brighter compared to the CMYK colour profile. You can also see that some colours are affected more than others when converting from RGB to CMYK.

Before converting your RGB design to a print ready CMYK file, the steps below may help print-proof your design and avoid unpleasant printing surprises.

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Using Photoshop's Gamut warning

Step 1 - With your design still in RGB mode (check this by clicking on Image in the top menu  > Mode), Save your design with a new name (File > Save as) as this will ensure that you still have your original and the changes you make when preparing the file for print will be done on a copy.

Step 2 - Go to the top menu and click on View and select Gamut warning:

In this example  I have deliberately used colours outside the CMYK colour space

When I select View > Gamut warning - this is what it looks like:

Everything that is grey is outside the CMYK colour space (there's not much inside!).

With Gamut warning turned on, you can add adjustment layers to carefully bring the colours back in gamut. Make sure you have Layers switched on (Window > Layers), and then click on the adjustment layer icon at the bottom of the layers window and select Hue/Saturation:

Create a Hue/Saturation adjustment layer

In the Hue/Saturation adjustment window you can tweak Hue, Saturation & Lightness by dragging the sliders left or right of zero (middle). 

Instead of altering all colours at once (Master), it is better to modify one colour at a time by creating multiple adjustment layers and correcting Reds, Yellows, Greens, Cyan, Blue & Magenta individually. To do this, start with the colour you want to bring back into gamut first: click the dropdown menu and select the colour closest to the one you are going to bring into gamut:

1. Do not edit the Master, because that will affect the whole image (not just the problem colours)
2. Select the colour you will be changing first (Yellow, Green, Blue etc)
3. Use the eyedropper and click on the area you are going to change.
4. If you find it hard to see exactly where the colour is you can turn off gamut warning for a quick peek.
5. Drag the saturation slider slightly to the left (to de-saturate the colour) until you see the colour come back into gamut (the grey will disappear).
6. Adjust the lightness slider (left or right) to further adjust the colour. 
7. Be careful to not drag the sliders too far: The aim is to fix the problem areas by adjusting the colours as little as possible.
8. Create a selection area for each new adjustment layer (see below) - this will help preserve the non-problem colours and allow you to adjust only what needs fixing.

TIP: Before you start it is a good idea (especially when you have a lot of out of gamut to deal with) to create a selection area of the out of gamut colours. Go to Select (in the top menu) > Colour Range - and select Out of Gamut. This will create a selection area. If you have a large selection area it is also worth to Feather the selection to create a softer blend between the selected and non selected area. Right-click and select Feather. Adjust the feather radius depending on the size of your image (I used 15 pixels on this image which was 800 pixels wide):

Step by Step Gamut correction
Top left: Yellow brought back into gamut |  Top right: Greens and some Cyan almost back in gamut
Bottom left: Cyan and Magenta coming back in gamut | Bottom right: The adjusted image.

If you want to make any final adjustments (Colour, Brightness etc), do this before converting to CMYK. Leave gamut warning on so you can see if an adjustment goes too far.

Converting to CMYK - and saving your file for print

When you have no grey left - all your colours are in gamut and you are safe to convert your image to CMYK for printing.

• Flatten the image (if you want to save the file with layers, make sure that you save it as a psd before you flatten it).
• Check that you are converting to the intended CMYK profile: View > Proof Setup
• Convert to CMYK by going to Image > Mode and select CMYK. 
• Save the image

The image on the left shows the adjusted, print ready version where I used Photoshop's gamut warning to correct colours. 

The image on the right is a straight conversion from RGB to CMYK (no adjustments). While the difference may not be huge, the adjusted version has more vibrancy in the blues and greens (which tend to be 2 of the main problem 'colours' when converting to CMYK).