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10-23-2007, 08:54 AM   #1
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Custom WB in Infrared on K100D?

I've read some threads on Infrared photography in the forum about setting a custom white balance for infrared photos. I know how to do custom WB on my camera, but can't get it to work with an infrared filter (Hoya RM72) on my lens. I keep getting the "NG", try again message.
I'm shooting infrared in RAW, so can do WB manipulation later, but I'd like to get it right in the camera if possible to reduce post-processing. AND I'd like to know if there's a trick I don't know. As I said, custom WB works fine without filter on, but not with it.
I tried setting it by pointing at grass, a gray card, and a white card. Nothing worked. Any suggestions?
Thanks,
Steve

10-23-2007, 09:49 AM   #2
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You should be able to point it at some well-illuminated grass. I have had times where it didn't work the first time, ir it did pick a temperature but it was way off. But the majority of the time, it works well. The only thing I can think of that might be keeping you from getting a reading might be not enough light on the grass. Infrared light doesn't bounce and scatter as well as visible, so anything in shadow will be far darker than in light. So if the sun isn't shining on the patch of grass you're using for WB, there's a good chance it's too dark to for your camera to lock on to a WB.
10-23-2007, 12:37 PM   #3
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Custom WB in Infrared on K100D?

Aerodave,
Thanks. Insufficient light may be the problem. It was somewhat overcast when I did the test. I've done WB in such light without an IR filter, but hadn't considered that it might not be enough with such a filter. It's much cloudier today, so I'll have to delay a re-test
By the way, do you recall what the approximate color temperature is of your custom WB'd infrared shots? I played around with some RAW IR shots I took this weekend in which I had used a daylight white balance and it seemed I had to take them down to the end of the scale (ca. 2000K) to get them looking like other IR shots I've seen that were taken with a custom WB.
Steve
10-23-2007, 02:12 PM   #4
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Generally, when I set a custom WB in infrared, it ends up in the 2500-3200 range. That results in grass that is most neutral in color. But this is complicated by the Tint adjustment that the camera seems to apply.

When I import into Adobe Camera RAW, and select "As Shot" WB settings, the program indicates that the tint setting is not 0. In the case of one RAW I just pulled up, it was -37. Setting this to zero makes it so no WB setting makes the grass neutral gray. So the tint is important, and there are really two variables to worry about.

10-23-2007, 06:37 PM   #5
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Custom WB in Infrared - K100D

As you suggested my failure to get a custom WB was due to poor lighting. We got a brief peak of the sun amidst the clouds this afternoon so I scurried out and managed to get a successful custom WB off the grass. Made a huge difference.
FYI, I opened with Adobe Camera Raw in Photoshop Elements 5.0 and ended up with a color temp of 3450 and tint of -30. I applied white point dropper tool to a patch of grass and that made the picture look really pretty good with Color temp of 2100 and tint -57. The vegetation was pretty white, blacks looked dark and sky had a faint sepia-like tint to it. Now, the sun that did peak out was late afternoon sun, so I do have to repeat this on a truly sunny day to get a feel for the range of color temp and tint values I get coming out of the camera.
I also am curious to compare results of setting custom WB on vegetation vs white and/or gray card. Will do that when a sunny day returns and post the results.
Thanks for the help.
Steve
10-23-2007, 09:01 PM   #6
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I've never been confident in the idea of using a white or gray card for checking color in IR. Then again, I've never tried it. My reasoning goes like this: Those cards are made (calibrated) to be neutral in visible light. The inks and materials used may not be neutral in IR...they weren't made with that in mind. Much like a visible green card is unlikely to look white in IR, because it's not the same material as living plants.

Of course, complicating the matter is that fact that color has little meaning in that spectrum...so who's to say what's neutral? It's accepted, however, that vegetation reflects IR light so strongly that it can be our definition of white in infrared. So I find that custom WB set to grass is a nearly fool-proof way of getting a pleasing balance of tones pre-processing. This is important because, as has been discussed on this forum before--setting it before isn't the same as setting it later, even with RAW.

As you are, I'm interested to see what kinds of results you might get using a neutral card. But I wouldn't be surprised to find that they're not quite the same as using plants.
10-24-2007, 05:57 AM   #7
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What would happen to ir wb if you just pointed the camera at the sunny blue sky and did custom wb? That is where the ir is originating from. Wouldn't it be like an incident meter? Would try it but no sun for two days straight here. Has rained the whole time.
thanks
barondla
10-24-2007, 08:42 AM   #8
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The blue sky would probably be a bad spot to use. That's because the IR light in the environment isn't really coming from most of they sky, but just from the sun. The sky is blue because it effectively scatters high-frequency blue light. Low-frequency IR light isn't scattered at well, and that's why the sky looks very dark in IR photos (and why shadows in IR are especially dark). The only good source of light for a white balance adjustment is something directly illuminated by the sun. A big white cloud might work well, but the clear part of the sky would probably not work well at all.

10-25-2007, 10:09 AM   #9
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QuoteOriginally posted by atnbirdie Quote
As you suggested my failure to get a custom WB was due to poor lighting. We got a brief peak of the sun amidst the clouds this afternoon so I scurried out and managed to get a successful custom WB off the grass. Made a huge difference.

Steve
Curious, did you have the filter on or off. It can make a bit of difference.

I use the CWB with filter on, less red tint to the original photo.

Dave
10-26-2007, 07:42 AM   #10
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I have never had a problem setting custom WB with an infrared filter. The thing to note is that the IR filter cuts out almost all of the visible spectrum and the sensor is in effect reading mostly from one channel, namely the red channel.

Method:
1) Pick bright green foliage/grass under a bright sun as the target to do the custom WB. This is because it reflects plenty of IR.
2) Go to manual mode and set an exposure setting that overexposes about 2.5 to 3 stops over what the camera meter recommends. Attach the IR filter on the lens.
3) If you're aiming at say green grass, make sure it fills the frame. Then do the custom WB.

You may need to do it a couple of times until the camera can do a reading.

With the K100D, with the filter on the lens, shoot in manual mode. To gauge exposure, I find that I need to set the exposure to be +2.5 over what the camera's meter reading. This amount can vary slightly as I have made comparisons with another K100D user. On his camera, he had to set at +3.0. Once you get a nicely exposed shot, the image should appear as a sepia coloured image on the LCD. Use the histogram to determine whether the shot is over or under exposed.

From then onwards, you can use Photoshop or whatever program to tweak the IR image. Even Pentax's Photo Laboratory is quite good here. Just set the white point at some area of green foliage and you'll get a pretty neat IR image (using a RAW file).

Last edited by creampuff; 10-26-2007 at 07:54 AM.
10-26-2007, 12:49 PM   #11
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Yes, with filter. That was what I was after, an IR CWB.
S
10-27-2007, 03:54 AM   #12
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Creampuff,
Yes, as I mentioned, I figured my problem was tryiing custom white balance under overcast conditions.
On my K100D, I find that an Ev of about +2 works fine. That puts the red curve all the way to the right of the histogram. I even, on occasion, get a little red clipping, so I think I'll be using about Ev+1.7 and doing a final levels tweak in Photoshop Elements.
With respect to setting white balance, I've set my custom white balance system to work by referencing only the center focusing point. In essence, when I do a CWB, it is spot metering. That reduces chance of including non-white areas in the WB sample.
Steve
10-27-2007, 07:07 AM   #13
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QuoteOriginally posted by creampuff Quote
2) Go to manual mode and set an exposure setting that overexposes about 2.5 to 3 stops over what the camera meter recommends. Attach the IR filter on the lens.
I was going to say something close to this -
attach the filter to the lens, then meter manually and change your settings until you get +2.5-3 stops overexposure according to the meter.

Then do your custom WB with that setting.
10-27-2007, 02:23 PM   #14
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Infrared Custom WB Test

All,
Just finished my test. Have a sunny cloudless day at last. Did Color Wh Bal (CWB) using grass, white card, gray card. Couldn't get CWB to register using gray card. Difference between results using Wh Card and Grass was negligible (Wh Crd gives about 100 deg cooler temp and a little bluer tint).
I too found that between using the on-camera EV of +2 (I was shooting in Av mode) and adjusting in Adobe RAW Converter, I ended up with a total Ev of about 2.7-3. In future, I will just shoot in manual to get it right in the camera. I'll err to under exposing using Ev 2.7 as a couple of +3s ended up with some clipping.
Using wh Bal tool in the RAW converter brought final results to look black and white with brownish sky (Temp 2050; Tint -58 to -60)
Interesting note is that when I shot one using AWB, it was of course very pink at first. Even after I adjusted its color temp to 2050 and tint to -58 to -60, it still looked decidedly pinkish compared to the cleaner B&W of the CWB shots. So even though I shot all in RAW, getting White Bal right in camera using CWB is very important.
Steve
10-27-2007, 04:15 PM   #15
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Your results mirror mine very well, especially the fact that getting WB right in camera is important, because it might not be recoverable later.

However, unlike almost everyone else here, I find that I only need to bump up the exposure about +1 to +1.7 EV, and usually more like +1. I don't know why my K100D would have better agreement betweenthe light meter and the sensor, but that's how it works. I usually shoot IR in manual mode and change Tv and Av while watching the exposure meter.
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