RAW vs White balance

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

Hello vortout,

Since you don't list your e-mail in your profile, I'll try to get in touch with you this way through the original post that interested me.

I think we now understand that Pentax DSLR's prior to the K10D modified their relative channel gains for different WB presets, including custom WB, in order to help avoid channel clipping.

However, the second part of your post has become interesting to me as I look into writing a general PEF codec for Vista. Again, it has become pretty well established that for ISO's higher than 400, the Pentax DSLR's prior to the K10D did their ISO sensitivity gain by bit shifts. What interests me is the difference between ISO 200 and 400 where the raw histogram for equivalent exposure appears to be half the width for ISO 400 and up as for ISO 200. This indicates that these cameras do nothing when switching between ISO 200 and 400 and that all ISO sensitivites above 200 only effectively use half of the 12 bit ADC reading range.

This should be compensated for when doing a raw conversion, but common applications such as ACR do not appear to do this. I can likely obtain sample raw files from forum members such as Jonas B to help confirm this, but I would like to be in communication with Anton Malykh to see what he has discovered and to thank him for writting the little Java application that started all this. Also, we seem to share some common interests in digital photography and programming. I see that you contribute to the same Pentax Club forum in Russia that he does and have visited that site, but I can't seem to obtain his e-mail address. Could you help arrange this, and perhaps send him my e-mail address from my profile?

Regards, GordonBGood

vortout wrote:

Hi Everybody

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 )

X – axis has maximum 4095 and Y one shows number of pixels
accordingly.

Test shots was done on a tripod with using of incandescent lamp

He used different white balance presets

So enjoy with samples:

AWB:

Daylight

Tungsten:

Manual WB

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

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.
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.

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

ISO200 1/5

ISO400 1/10

ISO800 1/20

ISO1600 1/40

ISO3200 1/80

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

So folk think about it. Any suggestions?

Post (hide subjects) Posted by
w
w
w
ddd
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow