Reality Check: a Head-to-Head Comparison
So what is the point to all this zone system calibration business? Take a look at these photos, taken with three cameras which have three different sensor types, exposed identically and processed using two RAW converters. This is what makes people say things like, “so-and-so RAW converter has a certain look to it.” Every converter, by necessity, has its own “look,” depending on how it translates the raw data from a particular camera into color values, and its default adjustment settings. The result is RAW conversion anarchy as you can see below. For these images, the background of the Cal-Vet sticker was placed on zone VII. Exposure was 1/60 at f/5.0, ISO 100. Each was processed with a medium contrast curve, zeroed adjustment controls, and either a generic or no camera profile. It may not look like it, but they were all spot white balanced, under the middle of the word “California.”
| Adobe Camera Raw | RawTherapee | |
| Sigma SD15 | |
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| Fujifilm FinePix HS30EXR | |
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| Nikon D800E | |
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It doesn’t have to be this way. With a color-managed and calibrated system, we can expect consistent results. First, we make a color profile for each camera to standardize its response. Here are the ColorChecker Passport images for the sensors above, each corrected with its own profile. (Tip: place the light gray patch, at the bottom left, on zone VII.)
This is a definite improvement; the images are now properly color balanced, but they still have quite a way to go.
| Adobe Camera Raw | RawTherapee | |
| Sigma SD15 |  |
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| Fujifilm FinePix HS30EXR |  |
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| Nikon D800E |  |
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So now we make an exposure series for each camera and process it in each RAW converter. Here they are, uncalibrated:
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| O | I | II | III | IV | V | VI | VII | VIII | IX |
Each series was calibrated to place zones I and VIII on the shadow and highlight threshold values, and zone V on middle gray, as described on the calibration and RawTherapee pages. The six calibration curves:
The six calibrated zone rulers:
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| O | I | II | III | IV | V | VI | VII | VIII | IX |
The final result. This time, each image was processed using the camera’s color profile, and the adjustment settings determined by the calibration above. They were spot white balanced as before. No further adjustment was made.
| Adobe Camera Raw | RawTherapee | |
| Sigma SD15 |  |
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| Fujifilm FinePix HS30EXR |  |
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| Nikon D800E |  |
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That’s all it takes! See also the summary page.
Next: “Let’s see you do that in Linux.”
