A tale of scanners, pictures and software (oh my!), Part 3: Calibration

Part 3. To calibrate or not to calibrate, aye, that is a question!

While doing the research on scanners I found a number of mentions of doing a calibration test on a scanner to judge its out-of-the box-color accuracy. Actually, what’s tested is mainly the accuracy of whatever color calibration information sets (color profiles) were provided in the driver for the scanner. Doing my research, I learned enough about all this to be ‘dangerous.’  I’m certainly no expert on this, but here goes with what I think might help you.

What’s the deal with calibration?

It seems obvious in retrospect, but a scanner really has no idea what the colors should be for your photograph. When doing a scan it gets a lot of numbers that are the color information for each scanner-created pixel, but there’s no way for it to know if the CCD sensor is right, biasing the information in some direction, or reporting completely bogus values. The exception is a scan of a calibration target (google “IT8 calibration target”) where it, in fact, does know what the colors should be.

Kodak Kodachrome IT8 Target

The target is a special photo, slide or piece of film that has a standardized array of consistently defined colors on it and a data file with the numeric values the scanner should get for each color patch. Combine that with software that knows how to use it and what comes out of a calibration run is a color profile for the scanner, a set of adjustment values that can be embedded into the driver software. The profile is used to correct any biases the scanner has so you get back a scan with the best color accuracy the scanner is capable of. To be precise, however, that profile is only accurate for the media scanned to create it, so for really exacting work, the scanner must be calibrated for each type of media to be scanned. With film (negatives), for instance, that means a different profile for every combination of {film manufacturer+emulsion type+year group}, e.g., Kodak, Kodacolor 100, 1965-1972.

When shipped from the factory, the scanner software has a set of profiles which may be that specific or entirely generic and the software may, or may not, let you choose between profiles. Even if it shows them to you, those profiles might excellent or they might be off for the specific hardware (serial number) you pulled out of the box. (Got a headache yet? I did!).

What I got out of all that was that having the option to do a calibration was important and that was a big reason I got the Vuescan software. Neither the Canon or the Epson software will create new color profiles, so to have that option, we need other software. The rub is that not only do we have to buy other software, but we also have the buy the targets, and they’re not cheap. Low-end targets run $35-$50 each and high-end, individually-checked targets for film can run hundreds, each. Ouch!

So, do we really care?  The answer it seems to me, with a couple caveats, is ‘no.’  The condition where I think the “don’t care” answer holds true is where we’re:

  • using a good, relatively new scanner that’s clean
  • scanning prints that are family snapshots or scanning black and white negatives from Kodak film
  • viewing them on a monitor with less than 4 or 5 digits in the price tag.

If any of those are false, then you might want to calibrate. To get color-accurate scans, my old scanner badly needed calibration, probably because of the fluorescent tube. With age, its brightness and color will change. The changes are slow, but significant over the 9-year time span I was dealing with. I could, and did, correct for it, but it was complicating an already painful process.  However, the quality of the material being scanned is more important. Even under good conditions, color prints will fade and color shift with age and the amount of fading and shifting is highly variable. So, if I calibrated my old scanner, I might get excellent color accuracy–but for these old prints, I’d have color-accurate but ugly results that I would still have to adjust by-eye on my monitor. Calibration of the scanner just lost its importance (and appeal) in this case.

Weakest link in the chain–your monitor!
picture of an LCD monitor. However, the real killer here is the fact that I’m making these color judgments based on what I see on my monitor. Even with a perfect print and a 100% accurate scan, what we see on the screen may not be right (match the print), unless you’ve also got a color- accurate monitor and it won’t be unless you calibrated it recently. I’ve got a good, but not top-of-the-line, monitor and it’s periodically calibrated. I can tell you from personal experience that monitor calibration is crucial. Mine seemed fine out of the box, but after calibration the difference was startling and so much better. If you do any photo (or video) work, you really owe it to yourself (and your images) to calibrate your monitor-it’s easy and the software/hardware package isn’t terribly expensive. The likelihood that your monitor was accurate out-of-the-box is close to zero and it also changes slowly over time (recalibration at least annually is recommended).

Conclusions

So, after all the research, what did I do? I recalibrated my monitor and bought Vuescan.

Picture of a Kodachrome film box.So far, that’s it. I decided that scanner calibration for prints is unnecessary right now. That’s based both on the review of the scanner hardware and the huge variability in the prints I’m scanning. For black and white negatives, the Vuescan profile set has given excellent results so far, so I’ll defer that calibration, too. Color negatives are a “maybe.”  So far I’ve not done any, but I’m betting I’ll be okay with the Vuescan set of profiles. For me, the one place where calibration is probably needed is Kodachrome slides. Everything I’ve read (and personal experience) says that these are exceptionally difficult to get good, color-accurate scans of and I have a lot of slides. My research indicated that Kodachrome is finicky enough to benefit from a hardware-specific and emulsion-specific profile if you want the best the scanner can do. So, investing in a Kodachrome IT8 target (~$50), and running a calibration seems like a good idea before I (someday) launch into that part of the project.

UPDATE (Sep 2011)
I did get the slide film calibration target and did the calibration process in VueScan for both of my scanners. The result did change the color profile for both of them but the difference was surprisingly small and subtle. At least for these scanners, I’d say calibration is nice, but not essential unless you’re doing work that is color critical.

“Take away” points on calibration

  • Calibrating your monitor is needed for any photo work and a ‘must do’ prerequisite for good scans.
  • Knowing that your scanner can be calibrated is important.

Calibrating a scanner is a good thing, but for most of us the cost-benefit ratio isn’t there, at least not for most kinds of scans. However, your needs might be different now or at some point in the future, so knowing the option is there seems important.

Next: Some ‘lessons learned’ you may find useful.

————————-
For more information on this topic I recommend starting here:

The VueScan Solution, by MIKE PASINI
Color Calibration Wikipedia
Monitor Calibration: Who needs it? (You, if you care about your photos)

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About Dick Knisely

Science-guy, engineer, father, grandfather, husband -- yeah, I'm all of those things. I author this blog to share things I care about and you might care about, too. I hope you do and that you'll join in to share things you care about.
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2 Responses to A tale of scanners, pictures and software (oh my!), Part 3: Calibration

  1. Pingback: A tale of scanners, pictures and software (oh my!) part 2: software. « Presentation Impact

  2. Pingback: A tale of scanners, pictures and software (oh my!) part 2: software. | What I think about that

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