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05-05-2009, 05:08 AM   #1
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replicating custom white balance in kelvin + offsets?

I have a K10D. I often take photographs in my girls' room, which has big green fabric leaves from Ikea near the ceiling. Bounce flash works great in there, but everything, not surprisingly, ends up with a green tint. Now, I can -- and do -- set the white balance perfectly with a gray card. But since the lighting there is always the same, what I'd _like_ to do is transfer that setting to one of the three custom white balance settings available.

Unfortunately, there's no way in-camera to read what the snapped white balance is (is there)? There's some possible information in the extended EXIF info, but I'm not sure exactly how to interpret it.

On the other side, the G-M axis and B-A axis settings in-camera are without units -- who knows what 1 step of GM compensation means? I mean, literally, "who knows"? Since the LCD isn't color calibrated (and unlike the K20D isn't even adjustable), it's hard to tell exactly what changes there are going to do. I never seem to be able to really get 'em right dialing them in.

My Olympus P&S camera had a feature where one could store three (or was it four? -- I forget) different shutter-set custom WB settings. That was infinitely more useful to me than the custom K settings -- even if I had expensive lighting with documented output, a gray card reading would probably be more accurate anyway.

(And yeah, I know that shooting in RAW would relocate the problem to my computer where I could address the issue in various ways. But I should be able to do this in camera, shouldn't I? Thanks in advance.)

05-05-2009, 01:20 PM   #2
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Matt, send me one of your images with the corrected white balance. I'll open it in Lightroom and get the colour temp readout for you. Then all you need to do is set that on your camera when shooting in the "green room".
05-05-2009, 05:27 PM   #3
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Thanks for the offer, Albert. I may take you up on it, but primarily this room is just an example of several places where the situation comes up. Because of the green cast it's a very good example, since it's more complex than just the kelvin temp. In fact, since I'm using the flash, I assume that it's basically the normal flash color temp (5000s, daylight-like) but with the green cast from the decorations in the room. I'm not sure how one would get that information

See the two attachments: in one, WB set with a gray card, and in the other, set to the Flash preset.

I notice there's some interesting fields in the EXIF:

Code:
Exif.Pentax.WhiteBalance                    Short       1  Manual
Exif.Pentax.WhiteBalanceMode Short 1 User-Selected
Exif.Pentax.WhitePoint Short 4 13984 8192 8192 10400
Exif.Photo.WhiteBalance Short 1 Manual
Code:
Exif.Pentax.WhiteBalance                    Short       1  Flash
Exif.Pentax.WhiteBalanceMode Short 1 User-Selected
Exif.Pentax.WhitePoint Short 4 8192 8192 8192 8192
Exif.Photo.WhiteBalance Short 1 Manual
So I guess one answer to my question would be: how to translate those values into something to enter back into the Kelvin setting + C-M offset / B-A offset grid. Not as convenient as saving settings in the camera, but it would serve my purpose well enough.
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05-05-2009, 05:49 PM   #4
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Matt, I wonder if those are the figures for the four channels (brightness, red, green, blue) used for the histograms? My personal way is to simply shoot RAW and spend time at the computer fixing things. I've subscribed to this thread, so anything you or anyone else comes up with will catch my attention.

05-05-2009, 05:57 PM   #5
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QuoteOriginally posted by Canada_Rockies Quote
Matt, I wonder if those are the figures for the four channels (brightness, red, green, blue) used for the histograms?
With just two bytes each (short int) it can't be the whole histogram. I suppose I can do a bunch of experimenting to see if I can obtain any sort of useful conversion....


QuoteQuote:
My personal way is to simply shoot RAW and spend time at the computer fixing things. I've subscribed to this thread, so anything you or anyone else comes up with will catch my attention.
Yeah, my theory is that the camera is already a little computer and it should be able to handle these simple things.
07-03-2009, 07:35 PM   #6
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Hah! From the K-7 manual:

"Saving the White Balance Setting of a Captured Image

You can copy the white balance setting of a captured image and save it as Manual White Balance."
07-03-2009, 07:53 PM   #7
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(although of course it'd still be way more useful if this could be stored into one of the 3 kelvin presets rather than the single custom/manual slot)
07-03-2009, 08:17 PM   #8
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QuoteOriginally posted by mattdm Quote
(although of course it'd still be way more useful if this could be stored into one of the 3 kelvin presets rather than the single custom/manual slot)
My K-7 will only arrive next week (hopefully !) but I've been rifling through the user manual.
It seems you can select from any photo stored in your SD card. If you are happy with the White balance setting of that photo, you just select it as your manual WB set.
Not quite the same as 3 memory presets, but I'm sure it can be useful.

In technical terms, the colour temperature kelvin setting is just a rough 1-parameter adjustment to the WB, which is really more complex than that. So while colour temperature setting is quick and easy, but its not going to be able to simulate a 1-1 match to a white card manual WB setting.

Actually, for me, the K-7's improved AWB as well as it greater flexibility with various WB adjustments is a very good reason to upgrade to the K-7


Last edited by kittykat46; 07-03-2009 at 08:26 PM.
07-03-2009, 08:32 PM   #9
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QuoteOriginally posted by kittykat46 Quote
In technical terms, the colour temperature kelvin setting is just a rough 1-parameter adjustment to the WB, which is really more complex than that. So while colour temperature setting is quick and easy, but its not going to be able to simulate a 1-1 match to a white card manual WB setting.
Yes, but you can also set offsets on Blue-Amber and Green-Red scales on top of the Kelvin number. Unfortunately, as per my complaint, the scale for that is unlabled and undefined, so the only approach is to hope it looks good.


QuoteOriginally posted by kittykat46 Quote
Actually, for me, the K-7's improved AWB as well as it greater flexibility with various WB adjustments is a very good reason to upgrade to the K-7
Ditto. Not a reason alone, but something I'm looking forward to.
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