Seeing all the shades of black

Working towards lifelike photos of dark paintings

The camera doesn’t always get it right. No matter how great your equipment and set up are, making a truly accurate photograph can be a challenge – perhaps one reason for the popularity of Instagram filters.

Museum photographers have to work at the edge of what’s technically possible when they photograph the world’s most precious artworks. As part of Operation Night Watch, we’re working with the Rijksmuseum to push those boundaries when it comes to color calibration.

On November 18, 2020, we had a chance to share our progress with the world’s most advanced museum photographers as part of a virtual conference hosted by the Association for Historical and Fine Art Photography. Presenting together with two technical photographers from the Rijksmuseum, AkzoNobel’s Senior Color Scientist Eric Kirchner was on hand to present what we’ve already discovered – and now he helps break it down for the rest of us.

What do museum photographers need to take a great photograph?

It’s actually very complex to take a photograph of a painting that reproduces the colors accurately. It requires expensive cameras and lenses, sophisticated lighting, expert software and a color-checker chart (a card with 140 standardized colors) to use as a test object.

Is the color-checker chart what you’re talking about when you talk about “color calibration”?

Yes, color calibration in photography is the process of fine-tuning everything until all 140 colors on the test object are photographed correctly, as compared to color measurement data for those 140 colors. If that process is successful, you can be confident that any color on the actual painting will be photographed correctly as well.

At AkzoNobel, we use color calibration for making sure color measurement instruments are correctly working. That way do-it-yourself shops can deliver the right color paints to their customers and car repair shops can make color-matched repairs, for example.

Sounds like you’ll be able to draw on what you’ve learned in other areas, not just the field of photography.

Precisely. The collaboration with the Rijksmuseum pairs our own color expertise with the Rijksmuseum’s expertise in technical photography. We each have a lot of knowledge to bring to this project, but we also stand to learn a lot from it.

For AkzoNobel, what we learn more about accurate color measurement can have business applications from how to best measure the color of a dark car in a matt finish or knowing what we should take into consideration when we develop consumer tools.

So how will better color calibration help to improve museum photography?

Museum photographers have noticed that the darkest areas in paintings are often less accurately represented in photographs than other colors. These color deviations are so subtle most people wouldn’t notice. But for scientific investigations of art works, especially very dark 17th century Dutch paintings, it’s an important discrepancy to solve.

The Rijksmuseum uses advanced high-resolution photography, where you can zoom right into separate pigment particles. This is possible by combining thousands of partial photos together – but of course to do this, you need all photos to be extremely consistent in color reproduction.

Why are the darkest colors the hardest to calibrate?

We had to do some real detective work with the experts from the Rijksmuseum to figure this out. We first thought that the problem may be caused by their color instruments. To begin our investigation, we designed a set of very dark paint samples in our labs.

In our car repair formula development laboratory in Bangalore, we designed a series of repair paints with neutral colors, varying from almost black to the blackest black you’ve ever seen. We also prepared a range of matt to high gloss samples using our Mix & Matte vehicle refinishes clearcoat. Finally, at our site in Sassenheim, the Netherlands, we prepared paint samples with very dark subdued colors – using flat matt wall paints from Dulux Valentine and high-quality trim paints with a satin gloss (Rubbol BL satin).

Then we used the samples to test the performance of the Rijksmuseum’s color instrument. Comparing its data with measurement data from one of our state-of-the-art, very expensive spectrophotometers, we could clearly see the color instrument wasn’t the problem.

Well, at least you knew the instruments were working. What turned out to be the real problem?

We then considered the way photographers typically use the 140-color test chart – does it result in large color deviations for the darkest colors?

We showed that the test chart itself is good, but the way camera data is often processed can be improved – especially for the dark colors. The good news is that the color instrument used by the Rijksmuseum, and by many other museums, is very capable of performing the required measurements. Our solution shows how the measurement data should be interpreted and how it should be used in the color calibration process.

That’s exciting! Is your investigation complete now?

No, we’re not done learning yet! There are many more aspects in technical photography that we need to address in order to make a next step in color accuracy. We still plan to investigate the impact of filters and fluorescence, for example. Our work with the Rijksmuseum continues…