Fri Aug 10 14:25:30 EDT 2007 Godfrey DiGiorgi wrote: > 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. >
This makes good sense to me. If it is correct, it brings up an idea (here goes a patent, but oh, well..): camera shooting modes or options (e.g. one of the "green" modes, or via a separate wheel/switch) such as "tungsten", "low light", etc. - which in addition to changing the WB also enable a different metering calibration. Igor -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
