How can I find a good CMYK approximation of a colour in the real world (e.g. on a wall)?

Question

Let's say I have a wall of some colour, but I have no way to determine the actual paint that was used. All I have is the eyeball impression in front of me.

How can I now work out a good CMYK colour that, when digitally printed (a) coated or (b) uncoated, will be as close as possible?

I know one approach is to buy a book of Pantone swatches but realistically this is expensive and overkill. I am not actually interested in Pantones and spot colours. I am printing in CMYK process. Do any similar kinds of swatch books exist just with process-printed swatches?

Or is there a better way altogether?

To be clear I'm not after extremely accurate matching. I'm just after a close approximation.

Answer 1

If you can't afford a new Pantone CMYK guide swatch book, have a look on ebay/amazon for a used one that's still in good condition. It should still be good enough for your purposes. Printers usually update their books often because the colours tend to fade over time, so perhaps even check with your local print shops. They might have an older one you could buy.

There are also guides which are not published by Pantone and which are a fraction of the cost. I found this one here: https://www.hellocolour.co.uk/#ultimate-colour-bible

Note: I have no links or affiliation with the linked website. I can't vouch for the quality of such guides, and can make no personal recommendation since I've never tried one.

Answer 2

There are several issues here.

when digitally printed (a) coated or (b) uncoated, will be as close as possible?

1. For a digital print, it is better to use an RGB file.

2. The result on coated and uncoated can be potentially extremely different, depending on if it is tonner based or inkjet-based.

I would not use a photo as a reference unless you have calibrated your scene+light+camera+lens with a Macbeth chart, which can be as expensive as a Pantone color chart, so let's go to the practical way and specific for your case.

Print your own reference car on the actual paper you need to use, both coated and uncoated.

Here is a color chart that you can use: https://otake.com.mx/Color/RGB-01-Letter-LowRes.png

Go back to the wall and compare the values. The values can be different on both prints, the uncoated will probably need to use lighter values because the print is most likely to be darker.

Now you have the exact value you need to use on your digital file on that specific printer with that specific combination of papers.

If you still need a CMYK value, you can convert the RGB file to CMYK. (Let me see if I can find my chart)

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If you need a real absolute value, you could need a Spectro-colorimeter.

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There are some other types of color charts cheaper than a Pantone one, called "Color atlas". This will be a good option if you need a CMYK value to be used on a comercial print, like offset. But you need to see what color profiles and specifications they used.

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If you still want to go with a photo as a reference, you need to take into account several things.

That different cameras have different flavors, for example, some can make your colors "pop" by saturating them, some will make the skin tones more neutral and the greens greener and blues bluer.

So you need to use a target, normally a Macbeth which is used to calibrate the camera+lens+light+scenario.

But you can do a basic calibration of the scene measuring the white balance of the light.

Here is an explanation of how to do that. https://photo.stackexchange.com/questions/61493/color-issue-studio-images-have-a-pink-hue/61497#61497

You also need to adjust the exposition using either a gray card or an incident light exposimeter.

Answer 3

In order to get a true color value from a photo, you have to be able to eliminate the effects of environmental color contaminants, like lighting and reflections. You can often eliminate reflections by adjusting the angle of the photo. For color contaminants, you need a known reference in the photo that you can use to recolor the image in Photoshop. Lots of photographers use a gray card. (https://en.wikipedia.org/wiki/Gray_card)

Take one photo with the card and one without it. Then, in Photoshop, adjust the colors of the image so that the gray card is "true." One good way to achieve this is to create a swatch in Photoshop that you know matches the output color of your gray card. This will require some testing, but once you have it, you should be able to use it indefinitely.* Once the gray card in the photo matches your swatch, your exposure and color balance should provide a print that represents the actual color very well. Apply those same color changes to the photo without the gray card for the final.

*One huge caveat for printing: Output devices vary greatly in their color temperature and even brightness. Be sure to create an accurate gray swatch for the intended printer if you don't have strong color control, like G7 or something.