Interesting Raw-format findings

Perhaps I should start setting the white balance properly on my Pentax *ist DS — it would appear that the camera actually pre-processes the raw data coming off the sensor based on what you’ve chosen as the white balance setting. This sort of goes against what I’ve been taught about raw files before — that the white balance setting (and indeed most of the picture processing settings) doesn’t matter. It would appear it does — the camera apparently does per-channel gain control, and then the processing software scales the channels appropriately afterwards. Sort of handy, but it would have been nice to know earlier: I always leave mine on “Daylight” white balance, and just fix stuff up afterwards — perhaps I’ll have to change this behaviour.

Also it would appear that ISO 1600 and 3200 are just software multipliers. If you look at the raw file data, there are holes in the graphs — indicating the use of a software multiplier. Which means that you’re better off using ISO 800 and underexposing by 1 or 2 stops (for ISO 1600 and 3200 respectively). It also seems that ISO 200 may be a bit weird, and that the sensor is actually best at 400.

(Note that all this only really applies to the Pentax *ist DS — it would appear that Canon cameras don’t do the same thing, although the Nikon D200 does: it’s an advertised feature.)

RAW vs White balance on the DPReview Pentax SLR Forum — you need to read all the posts, people were initially skeptical but seemed to be convinced in the end.

Needless to say, at some point I’ll have to test this for myself. Fetch me a grey card!