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I have a physical color chart of paint that I wanted to digitize and I wanted to archive the visual perceived color of the paint. The paint were painted on transparent plastic sheets. I have been doing it using a calibrated flatbed scanner, but recently I found out that the paint chips reflects very strongly to close light source, making them super saturated than what they normally look. So I'm now looking for other ways to accurately archive them.

One setup I can think of is to use a product shooting setup, with a lightbox and the light source positioned a foot above the paint chip, and then shoot it with a digital camera. But I am completely new to this. I need advice for better setup, camera choice and method of calibration. In scanner, I can calibrate the scanner with an IT8 target. Can I use that to calibrate the camera?

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2 Answers 2

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You cannot calibrate a digital camera. You can, to a lesser degree, adjust how the camera sensor's output is converted into a color image; but I think "calibrate" might be too generous of a term for that.

What can, and should, be done to ensure accurate colors is to make sure you use a full spectrum light source to illuminate the paint chips... e.g. flash and not LED. And that the white balance of the image is adjusted for any color bias of the light source used (e.g. if halogen bulb was used instead of xenon flash).

Using a full spectrum light source ensures that the paint chips can reflect/absorb all wavelengths as they naturally would (i.e. in sunlight). The white balance adjustment can be done using a color checker target like the IT8; or using any known greyscale target (kodak grey card). Take a picture of the test target, and use the white balance adjustment/settings for all other images.

Calibration of digital images is mostly achieved by calibrating the output device; i.e. the monitor or printer that will create the viewable image. But since the image files are for archive purposes, you really will not have any control over that in the end; so that calibration step can be left for whoever is wanting to view the images in the future.

Also, get the exposure as accurate as possible at the time of recording because exposure shifts in post will also affect/change the color accuracy of raw files (because it changes the RGB luminance values that are demosaiced into the displayed colors).

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  • \$\begingroup\$ What is this flash that I need? Like the flash from the camera? What is the shooting setup? I have a x-rite colorchecker passport for the gray card. \$\endgroup\$
    – reddy
    Commented Mar 2 at 15:54
  • \$\begingroup\$ No specific flash, only that it is full spectrum. Almost any would do, but on-camera is probably not ideal as it is likely to be too direct/hard. The shooting setup isn't anything specific, just ensure that the lighting isn't contaminated, and that it is even... bouncing the light off of the ceiling/walls (i.e. lighting the room) is one option, a large softbox is another, or outdoors out of direct sun/lightly overcast skies. But the more controlled/consistent the light/setup is, the better the results will be. \$\endgroup\$
    – Steven Kersting
    Commented Mar 2 at 17:20
  • \$\begingroup\$ I'm still confused, is the full spectrum flash some kind of light bulb, like what is the name? The setup I get from your response is something like a dark room, a white backdrop to place the paint chip on, and then a softbox with the full spectrum light to light up the paint chip? Is that correct? And what kind of camera do I need? \$\endgroup\$
    – reddy
    Commented Mar 2 at 19:05
  • \$\begingroup\$ Any flash... i.e. a speedlight, studio flash, etc. Or any other black body emitter type of light (creates light by burning) e.g. halogen, xenon, incandescent, etc. You could even go with an LED or a fluorescent IF it has a very high CRI rating (98) AND that rating was accurate (it often isn't). But the basic setup you described would work. The camera is also not specific; they will all have their own/different spectral response curves, and there's nothing you can really do about it. Setting the WB with a known reference is about the best you can do. \$\endgroup\$
    – Steven Kersting
    Commented Mar 2 at 22:08
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    \$\begingroup\$ Update, after a few days of researching, I think I have found the solution in this Calibrite Grafilite lamp, the light is soft, it is CRI 95+ by a reputable brand and it is simple to use. I don't have to deal with all the camera settings with using a speed light and I don't have to worry about the all those light box brands lying about their CRI, I have read review that complain about the light in those light boxes are actually CRI 80 instead of the claimed CRI 95. And it costs about the same or even less than the other solutions. \$\endgroup\$
    – reddy
    Commented Mar 9 at 6:56
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Yes, with the right software.

I know Vuescan for example lets you use IT8's for image correction as well as device correction.

Gretag Macbeth had a specific many-patch portable target meant just for camera color correction called the 'ColorChecker SG Digital' that's now sold by Calibrite.

Picture Window Pro has/had a 'match reference' dialog which would let you select whether your image was something like a Color Checker and then line up the sampling areas. I'm sure there are similar systems for Photoshop even if you have to add them as a plugin. For the modern ColorChecker derivatives the vendor supplies the software.

One caveat I've noticed is that this tends to limit the dynamic range to that of the medium of the target. So often this can result in clipping of highlights or shadows. This is a good reason to use something better than just a plain matte classic ColorChecker.

To use a target just shoot the target with the same settings and light as the picture you want to correct. That way the correction for the target matches the correction for your image.

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    \$\begingroup\$ I have realized that my IT8 target was too small for shooting so I have to go for bigger chart. I did checked out the Calibrite ColorChecker SG, but it is a ridiculous $370 for 140 patches. Silverfast also has a good chart but they discontinued it years ago. So I ended up going with the French CMP Digital Target Studio Edition, big chart with 988 patches. One question I have with the shooting is that since all the targets were measured in D50 illuminant, do I also have to shoot in 5000K lighting? \$\endgroup\$
    – reddy
    Commented Mar 6 at 0:44
  • \$\begingroup\$ @reddy I guess you'll find out. I'm assuming no if they were measured relative to D50. IF they were some sort of absolute measurement? Maybe? It should work for anything shot with the sun. \$\endgroup\$
    – davolfman
    Commented Mar 6 at 1:22
  • \$\begingroup\$ I think I may still have an A4 IT8 target glued to matteboard I bought years ago years ago from Wolf Faust, I think? My worry with more patches is alignment. \$\endgroup\$
    – davolfman
    Commented Mar 6 at 1:26
  • \$\begingroup\$ You do not have to shoot in 5000k lighting. The color corrections will adjust the lighting in the images to the 5000k reference. Any resulting prints would need to be viewed in 5000k lighting in order to be 100% correct. And any digital display would need to be calibrated to output the colors correctly. But those last two variables are outside of your control. \$\endgroup\$
    – Steven Kersting
    Commented Mar 9 at 13:35

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