On Aug 10, 2007, at 10:41 AM, William Robb wrote: >> White balance should be of no consequence, although it's possible >> that changing the white balance somehow affects the metering >> calibration ... dunno. Although it is true that imaging and metering >> sensors are more sensitive to light in the red/IR range than in the >> green/blue range, and incandescent light is shifted way into the red >> range, so maybe the adjustment to WB could affect it in that way >> somehow... > > I've always been a little vague about precisely what white balance > is doing, > I've alway presumed that it is adjusting the gain of the colour > receptors. > If so, is it possible that the exposure variance could be generated > by the > voltage multiplier, not the exposure system itself?
The white balance setting isn't necessarily touching the hardware at all. In most cameras, it is an adjustment to the image processing parameters used to convert the linear gamma, bayer-matrix RAW sensor data to an RGB channeled, gamma corrected representation. In some cameras, it *might* touch the data in the pre-RAW processing that happens between the sensor and the A-D converter, but I have seen no evidence that this is the case in the *ist DS body, and little to indicate that it in the K10D body either. The main linkage between white balance and exposure is likely in a connection between the camera's exposure control software and those image processing software parameters. The DS body's metering calibration was definitely tuned to produce good results for the standard default settings on the Auto Picture mode ... bright color setting, JPEG capture, etc. Changing to RAW capture, the metering calibration does not change even though the exposure requirements of a RAW capture are quite different due to the wider dynamic range and gamut possible. Setting the White Balance in RAW capture mode affects the JPEG preview and thumbnail, the histogram and saturation blinkies ... it might also affect the metering calibration. By Igor's experience, I'd say this last is possibly true, but I'd have to do some testing to say for sure. Godfrey -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
