RAW vs White balance

Started Nov 20, 2006 | Discussions thread
GordonBGood Veteran Member • Posts: 6,308
Re: RAW vs White balance

As interspersed with images removed:

vortout wrote:

There is very interesting results for RAW files done with different
presets

One fellow on a Russian Pentax forum made a very simple program
reading Pentax RAW file and showing histogram for all 3 channels. (
http://www.penta-club.ru/forum/index.php?showtopic=19120&st=0 )

He used different white balance presets

So enjoy with samples:

AWB:
http://img89.imageshack.us/img89/7518/imgp9705pefsrl2.jpg

Daylight
http://img291.imageshack.us/img291/9208/imgp9706pefszp6.jpg

Tungsten:
http://img149.imageshack.us/img149/3917/imgp9707pefssi3.jpg

Manual WB
http://img148.imageshack.us/img148/3273/imgp9708pefsff4.jpg

As you see files are different not only on the header level but
also it is different physically for red channels.

I don't see that at all, as if the gains for the red and blue were changing as for a WB setting all the way from Daylight to Tungsten, then the Blue channel would be prevalent for one and the red for the other. All I see is a possible reduction of exposure for the Tungsten WB setting to allow for more headroom on the Red channel to avoid clipping if the aperture, shutterspeed, and ISO were exactly the same for these changes in WB. Since we don't have EXIF data, are you sure that these settings didn't change between the shots?

Conclusions from forum:
1. Your WB settings can lead to overexposure for RED channel but it
is not proved yet since may be it just a way to turn down 3rd party
converters.

I don't see that as above.

2. It looks like that 3rd Party converters except SilkyPix do not
know about WB behavior and that’s why there is some strange color
development results.

That's one of the hardest, although most important, parameters to dig out of manufacturers custom raw image files without spending a lot of quality time doing comparisons of the files shot in controlled conditions with controlled changes in WB settings, unless the manufacturer is so kind as to provide details on the file format. So likely SilkyPix and Adobe ACR are the only ones to do so. Dave Coffins dcraw is often wrong on this critical parameter.

Also there are some examples for the histogram for different ISO
settings.

ISO200 1/5
http://img244.imageshack.us/img244/2150/imgp9716pefsev0.jpg

ISO400 1/10
http://img151.imageshack.us/img151/884/imgp9717pefsjp0.jpg

ISO800 1/20
http://img168.imageshack.us/img168/4219/imgp9718pefsii8.jpg

ISO1600 1/40
http://img169.imageshack.us/img169/919/imgp9719pefscm7.jpg

ISO3200 1/80
http://img135.imageshack.us/img135/2221/imgp9720pefswz8.jpg

Conclusions:
1. There is not 1 stop between ISO200 and ISO400

Are you sure that the aperture was controlled between the ISO200 and ISO400 shot, as I would be very surprised that exposure would be wrong by this amount between these settings?

2. ISO 1600 and ISO3200 are rather software made and shall not be
used in RAW mode since you can fix exposure in during RAW
conversion.

Yes, for the D cameras that has been observed several times, and I think I saw some similar results posted for the K100D. However, whether you do the conversion yourself in raw or use the camera settings won't make any difference to the final result. Since the lost bits are pretty much below the noise floor, there won't be anything significant lost in the way of Dynamic Range and as for banding, even if one could notice these gaps in tonality, they will pretty will be filled in by the dithering effect of further processing.

As an aside, the K10D may do all of its ISO sensitivity gain using "software" digital gain, but with a 22 bit ADC there are never any gaps between tonality steps, so it's not a problem exept that readout noise would be directly proportional to ISO sensitivity, if true.

Regards, GordonBGood

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