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mburns's Journal: Calbrating digital cameras 3

Journal by mburns

My Samsung ST65 camera actually has a contrast control, and I have now realized that the proper setting for it is not zero. The default setting enhances contrast in the shadows and compresses the highlights. A -2 setting for contrast balanced by a +2 setting for saturation improves the appearance of the gray scale on a picture of the Color Checker 24 card. This might not be the final word - I will look at -1, +1 as well; but I have no desire to do post processing on photographs from this camera.

I have been trying to calibrate a Wolverine Data F2D14 film to digital converter. I now find that the color curves for this product are customized in a woefully unfaithful style. There is a big deficit of green in the lower midtones, and a huge deficit of red there. And there is a general surplus of blue from near black to near white. It is barely within the capabilities of the RawTherapee software to compensate for this using custom color curves.

My Canon EOS Digital Rebel, the 2004 model, works very well with the UFRaw software for post processing. The free software color matrix borrowed from the work of David Coffin makes pleasing color even compared to the ICC calibrations from Canon. But there is no natural calibration for the exposure setting and white balance. For a Color Checker 24 photographed against a dark background, the exposure setting in UFRaw should be -1.36, the temperature setting should be 5660, and the green balance .98. The exposure setting needs to be higher for most photographs. I use the "absolute colorimetric" setting for color intensity.

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Michael J. Burns

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Calbrating digital cameras

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  • I see that the ST65 overexposes in order to suppress noise. ISO 200 is actually ISO 80. This causes the high contrast naturally. I wonder if custom color curves in RawTherapee together with the low contrast setting on the ST65 can result in highlight recovery, while still taking advantage of the noise reduction from overexposure.

    • by mburns (246458)

      So now I will probably use the ST65 at ISO 200, -1 contrast and +1 saturation. The pixel noise might be tolerable for down mixing to 2 million pixels and posting at Google+.

  • UFRaw does use a white level and balance that are set from the camera and the color matrix. In fact the photographic levels are truncated to the white level as given. So my expectation of being able to recover the highlights from an overexposed subject is frustrated. But just click the button to get the white balance from the camera. And set the camera's notion of the exposure by putting the flat truncation to the top of the graph using the exposure slider.

Yes, we will be going to OSI, Mars, and Pluto, but not necessarily in that order. -- Jeffrey Honig

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