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Doug Kerr
Guest
Hi, Michael,
It is great to see a forum area devoted to this topic.
You have often emphasized the desirability of utilizing, as a target for white balance "calibration", a test target that was not only reflective-chromaticity neutral but which had a reflectance in an appropriate range. (Read, "well higher than 18%".)
I wonder if you could expound a little on the optimum reflectance issue. As I understand it, the premise is that an exposure result for the target that lies in some upper region of the camera's response will best allow the camera (or WB analysis capabilities in a raw converter) to most accurately determine the chromaticity of the reflected light from the target (and thus the chromaticity of the illumination, which is what we really seek to detemine in this exercise).
If the image of the target does not fill the entirel frame (or at least the area of metering sensitivity), then in a metered test shot, this "fairly high" exposure result for the target of course would come from a target of relatively high reflectance (essentially, a reflectance that is high compared to the actual average reflectance of the whole scene).
Of course, if one has taken a metered "frame-filling" shot of the target for WB calibration, it would not seem that the reflectance of the target would matter - the exposure result will be whatever the camera's metering calibration produces for a uniform-luminance scene. But perhaps that is not the practice of most interest.
Am I at all on the right track here?
Thanks.
Best regards,
Doug
It is great to see a forum area devoted to this topic.
You have often emphasized the desirability of utilizing, as a target for white balance "calibration", a test target that was not only reflective-chromaticity neutral but which had a reflectance in an appropriate range. (Read, "well higher than 18%".)
I wonder if you could expound a little on the optimum reflectance issue. As I understand it, the premise is that an exposure result for the target that lies in some upper region of the camera's response will best allow the camera (or WB analysis capabilities in a raw converter) to most accurately determine the chromaticity of the reflected light from the target (and thus the chromaticity of the illumination, which is what we really seek to detemine in this exercise).
If the image of the target does not fill the entirel frame (or at least the area of metering sensitivity), then in a metered test shot, this "fairly high" exposure result for the target of course would come from a target of relatively high reflectance (essentially, a reflectance that is high compared to the actual average reflectance of the whole scene).
Of course, if one has taken a metered "frame-filling" shot of the target for WB calibration, it would not seem that the reflectance of the target would matter - the exposure result will be whatever the camera's metering calibration produces for a uniform-luminance scene. But perhaps that is not the practice of most interest.
Am I at all on the right track here?
Thanks.
Best regards,
Doug