Converting an image from RGB to CMYKA tutorial by Natalie Latouf

RGB vs. CMYK

RGB• Red, Green, Blue• Additive Colors• Based on the emission of light• Their combination yeilds white• Their absense yields black• Use: Web (i.e. monitors)

CMYK• Cyan, Magenta, Yellow, Black• Subtractive Colors• Based on the absorbtion of color • Their combination yeilds black• Their absense yields white• Use: Print (i.e. paper)

What’s the difference?

Purpose of this tutorial

Let’s say you’ve got a fabulous image you’ve been using on your website.

You’ve decided that you want this image to be a key image in your new brochure.

If you were to simply print this image as is, it wouldn’t look quite the same.

Why? Because the printer uses CMYK (ink) to print,

unlike your monitor, which works in RGB.

This means that some colors that appear on your screen are simply impossible to be

replicated in print, so your picture would look different.

To control this difference, we must manually convert your image from RGB to CMYK in

Photoshop.

So we want to get to a point where you’ll be able to get exactly what you see on screen at

the time of printing.

Step 1Open the image that you want to convert in Photoshop. Notice at the top of your file window, the color mode will appear as RGB.

Step 2The next thing we want to do is find out which colors are out

of the CMYK Gamut - in other words, which colors can not be replicated in print. To do this go to View > Gamut Warning.

Once you click Gamut Warning - you will find that certain parts of your image will appear in grey (see above).

This grey area covers all the colors that are out of the Gamut. Our goal then is to remove all this grey area.

Step 3Let’s select this grey area (the colors that are out of the CMYK gamut). Click Select > Color Range and choose “Out of Gamut” in the first option in the window, and click OK.

Step 4With the grey area selected, we now want to create an

adjustment mask and desaturate the colors until we reduce the grey area and thus find colors within the CMYK gamut.

To do this, in your layers pane, select ‘New Fill or Adjustment Layer” (button located at the bottom of the pane), and select

‘Hue/Saturation’.

Step 5Reduce the saturation using the slider and you will find that the grey area in your image begins to shrink.

Don’t reduce it all the way, as the area will be completely desaturated. Simply adjust the slider until a large portion of the grey area disappears, while maintaining the integrity of your original image.

Less grey area, still vibrant. This is what we’re looking for.

Step 6Let’s get rid of the rest of the grey area.

Create another Hue/Adjustment layer exactly as you did in Step 4. Now reduce the Saturation until all (or most) of the grey

area disappears.

Now that’s too desaturated. So with this new adjustment layer selected, hold down Alt + D to create a Layer Mask. The grey

re-appears.

When you click Alt + D, your adjustment layer will change from white to black, and your grey

area re-appears.

Step 7Use a brush (with white as your color) to brush over the grey area, and you’ll find again, your grey shrinks.

Repeat this step until your grey area is no more.

You can even try adjusting the vibrance slider to see if that will help replace your RGB colors with CMYK colors appropriately.

Step 8When your grey area has disappeared,

go to Image > Mode > CMYK Color.

Your image will then be converted from RGB to CMYK without the software making any color adjustments (as you’ve manually

made them yourself).

And now, you’re ready to print.

End of tutorial.