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02-09-2009, 07:28 PM   #1
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Color temperature with gray card

I have a quick question about using the gray card and color temperature.

I was at Zion national park this weekend and I was shooting some pics I placed my gray card on the ground to use it as a in Lightroom for post processing.

In Lightroom, using the white balance tool shows the gray card at 50000k, with +2 tint. Does this temperature sound reasonable? The pictures look OK with this reading, I just wanted to make sure this wasn't a issue with the way I was using the gray card. From what I've read normal WB ranges are in the 3000-10000 range.

The day was overcast, and it was near sunset. Below is a sample picture.

http://www.flickr.com/photos/senojobmij/3268434062/sizes/m/

On another note, I didn't notice the K10D took this at 1/20 sec handheld until just
now. Go SR I suppose.

Let me know what you think, thanks.

02-09-2009, 07:33 PM   #2
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I don't check white balance with a gray card; I use a bright white cloth. Here is a link that describes it better than I could.

Photography Rulez: K10D Manual White Balance
02-09-2009, 07:51 PM   #3
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If the gray is neutral, it will work fine. I assume you meant 5,000 and not 50,000K?.
02-09-2009, 10:38 PM   #4
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QuoteOriginally posted by SpecialK Quote
If the gray is neutral, it will work fine. I assume you meant 5,000 and not 50,000K?.
No, I meant 50,000k.

I think it might just be some wierd Lightroom thing, but even just clicking around the pictures with the whitebalance tool and the majority of the color temperatures it's indicating are in the 20,000k+ range... I was just confused since this seems high, even though the pictures, to my eyes, look normal.

Playing with Lightroom, I can't really tell the difference between 20,000k and 50,000k, so maybe its something buggy with Windows 7 and Lightroom 64bit.

02-10-2009, 05:59 AM   #5
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Thanks for the link


cheers
02-10-2009, 06:25 AM   #6
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I personally wouldn`t use anything but a grey card at this point (possibly a Whibal). I usually set the white balance before taking shots so that I can guage colours real time during the shoot.

An 18% grey card is supposed to be neutral and are probably a lot closer than some hunk of old sock you find in a drawer But as they say, close enough for rock and roll.

I worry about using something white for balancing due to the risk of over-exposing during the white-balance reading. If that happens then your camera will think that no adjustment is needed and your white-balance will be entirely wrong. Even if you only clip 1 or 2 channels, your WB is still wrong.

- Andrew
06-13-2009, 08:09 PM   #7
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QuoteOriginally posted by deaner Quote
I don't check white balance with a gray card; I use a bright white cloth.
As stated, don't use pure white to do white balance. Use neutral gray. Using white will surprisingly give you a wrong balance now and then, because of blown channels.
06-13-2009, 09:17 PM   #8
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QuoteOriginally posted by senojobmij Quote
No, I meant 50,000k.

I think it might just be some wierd Lightroom thing, but even just clicking around the pictures with the whitebalance tool and the majority of the color temperatures it's indicating are in the 20,000k+ range... I was just confused since this seems high, even though the pictures, to my eyes, look normal.

Playing with Lightroom, I can't really tell the difference between 20,000k and 50,000k, so maybe its something buggy with Windows 7 and Lightroom 64bit.
Other processors have had color temp anomalies w/ Pentax files... This would not be out of the realm of possibilities. 50000 is just plain wrong.
Any Lightroom updats currently available.

06-14-2009, 04:09 AM   #9
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QuoteOriginally posted by AndrewShirley Quote

An 18% grey card is supposed to be neutral and are probably a lot closer than some hunk of old sock you find in a drawer But as they say, close enough for rock and roll.


- Andrew
Your use of 18% for gray cards triggered and old memory from Photo Dip days. This link says it all Meters Don't See 18% Gray by Thom Hogan.

FWIW I have stopped using gray cards and now use the folding white devices with good results.

David
06-14-2009, 08:12 AM   #10
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QuoteOriginally posted by David Quote
Your use of 18% for gray cards triggered and old memory from Photo Dip days. This link says it all Meters Don't See 18% Gray by Thom Hogan.

FWIW I have stopped using gray cards and now use the folding white devices with good results.

David
Sorry if this is OT but with regard to what the sensor sees as neutral gray. I noticed that in the discussion of uniWB they specifically speak of a magenta color as what the sensor sees as Neutral, I am wondering why no one is building a neutral magenta card to set exposure.

GUILLERMO LUIJK >> TUTORIALS >> UNIWB. MAKE CAMERA DISPLAY RELIABLE
06-14-2009, 01:02 PM   #11
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R

QuoteOriginally posted by WheresWaldo Quote
Sorry if this is OT but with regard to what the sensor sees as neutral gray. I noticed that in the discussion of uniWB they specifically speak of a magenta color as what the sensor sees as Neutral, I am wondering why no one is building a neutral magenta card to set exposure.

GUILLERMO LUIJK >> TUTORIALS >> UNIWB. MAKE CAMERA DISPLAY RELIABLE
This technique is really only for WB and neutralizing your histogram. It's not technically exposure related.
It would only be good for daylight and flash (technically only for particular cameras and particular light). You need a cyan card for tungsten. Also you need to either filter your light or lens w/ the same filter.
The uneven sensitivity of silicon is what causes your camera to use "channel multipliers"... you really want them set to 1:1:1 but the only way to do that is increase r/b (in daylight/flash) and or decrease green. This is what the magenta filter does.... Then you can increase exposure to compensate.
06-14-2009, 04:10 PM   #12
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Thanks for the explanation, I was just thinking out loud here and see by your explanation that it really wouldn't work like how I expected. Guess I'll stick with a Gray Card.
06-16-2009, 09:25 PM   #13
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A couple months ago I did a little test in tungsten lighting comparing use of gray card (actually gray Pelican case) and white paper. The setting from the gray card was much closer to neutral than the white which came out a bit warm--still influenced by the tungsten? Had intended to test outdoors in shade, under haze and in sunlight but never bothered--shooting mostly film this past month or so...The result was enough to steer me toward gray rather than white, but again, still need outdoor tests to really "sell" me. Since the perception of color is pretty subjective, I'd say test gray and white for yourself and use whichever you prefer...both were better than any of the in-camera white balance presets.
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