First let me state quite clearly that the Pentax K-x AWB (Auto White Balance) works really well for me for most of my shooting - it is definitely and noticeably better than my K100D - (in fact I would almost go as far to say "miraculously" better).
However once in a while I have found some difficulties under what can only be described as more extreme conditions where even manual white balance probably would not help.
At first I thought it may be attributable to modern LED stage lighting where the LEDs used to make up any color are just Red, Green and Blue LEDs - which have very narrow wavebands - thus giving very peaky spectrum without any real in between color content see my Post #
44 (link) above - and the whole thread -
Modern LED Stage Lighting & photography problems)
However with more usage I realized it's not just narrow band LEDs - although they do very much aggravate the situation further and they are becoming more and more prevalent - so one just can no longer avoid them - but it appears to be any strongly mono-colored lighting - eg: red gel filtered tungsten light, or worse magenta gel filtered tungsten light.
I think this may also be an intrinsic difficulty with any digital camera using the Bayer matrix sensor - which is just about all the commonly commercially available cameras..... for a really good explanation please see post #
341 by Canuke over at 4Sevens' CPF MarketPlace.
It appears that our dSLRs (and almost any digicam) cannot capture all that we can see - no matter how well the color accuracy is rated - as that is analyzed by computer from digital images of a Macbeth chart - and reference itself is a capture digital image from guess what? a digicam so that's almost a self-fulfilling benchmark?
Anyway deep reds are not captured by Bayer matrix digicams and rendered somewhat orange and processing can help "fake" it sometimes by balancing out (ie: having less of) the opposite/complementary color.
I have found that the K-x does have difficulties with more extreme colored lighting -
here are some examples and compared directly with my Canon G10 compact which seems to cope somewhat better with the extreme lighting
(all photos no PP other than resize and level 1 sharpening -
all should have EXIF data attached -
caveat: PhotoBucket can sometimes mysteriously drop metadata)
First mainly red gel tungsten lighting to show the problem is not isolated to LEDs -
K-x No Flash
Canon G10 No Flash
similar rendition eg: the three people at the front in more normal "white" lighting -
but notice how the G10 image seems to have more separation in the red area - thus showing more detail - eg: look at the bassist's face - it's not just exposure - but the difference in the way the two cameras do their respective white balance.
I have found sometimes using weak flash can throw some "white" light onto the scene which helps mitigate some of the problems with strong mono-color lighting - same scene with weak flash -
K-x with slow-sync flash (-1 stop flash compensation)
notice that the flash does help to improve the balance and lack of separation...
Canon G10 with slow-sync flash (-1 2/3 stop flash compensation) -
the G10 is just "better" in rendition - but at least it's not that dramatic a difference - although the K-x image still has mushy details in the vocalist's and bassist's faces - this is definitely due to JPG compression - but the Canon G10 images do not have this problem and they are smaller files and have had exactly the same degree of JPG compression.
OK now for some more radical LED stage lighting -
K-x No flash -
Canon G10 No flash
WoW1 what a difference in rendition - the G10 image full-sized is pretty noisy as it is at ISO800 for a tiny sensor - K-x has no such problems - but the color rendition problems are ginormous compared to the G10, notice the over-saturation of the bass and part of the shirt to glaring white (rightmost person) this is not just overexposure - but the K-x not coping with the extreme magenta lighting so it's clipping the either the red or blue channels or both.....
Look also at the bass drum how ell the G10 image shows compared to the K-x image where the colors seem to be melting into each other.
How about mitigation using flash?
K-x slow-sync flash (-1 stop flash compensation)
Canon G10 slow-sync flash (-1 2/3 stop flash compensation)
the G10 flash shot looks worse than the G10 no flash -
the K-x seems better than its no flash - but look at the bassist.....
Does post processing improve things - of course it does (no EXIF) -
K-x No flash shot
just adjusted brightness/contrast - not that much better
selected white point on guitar's white pick guard - does make the nearer two people look better.
How about the worse looking G10 flash shot?
now this looks almost as good as the G10 no flash shot - so it was just exposure - probably the flash's reflection from the silver keyboard front had fooled the flash metering of the G10.......