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Old December 29th, 2009, 08:18 AM   #1
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White balance confusion

My understanding of white balance is getting confused, partly from a video blog I watch and partly from an experience balancing my EX-1 last week.

First the blog. It's a relatively well-know V-DSLR blogger who repeatedly said he was "turning up" the white balance to warm up the image. He showed an image at what he claimed was 6000K that was noticeably warmer (more "yellow" ) than an image shot at 5000K.

Isn't this backwards? Shouldn't the image be cooler at 6000k (since daylight is 6000 and tungsten is 3200) than 5000k?

Last week I was using Warm Cards to WB my EX-1. I've done this a hundred times without really looking at the k value produced. I started with a white card: looked nice to my eye and produced a value of around 4100k. I then went to a 1/4 warm card (which is light blue in color) and got an image that registered 4700k. Nothing else about the setting changed: same overhead flourescent lights, held in same spot etc. 4700 is "cooler" than 4100, isn't it? Indeed the image looked cooler, not warmer.

I thought I had a good understanding of this from still photography (where on my Nikon setting a WB of 3400 makes the image warmer) but between the blog post and last week's experience, I'm wondering if I have it backwards.

Thanks for the reality check.
Bob
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Old December 29th, 2009, 09:54 AM   #2
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If you balance to a cooler light (higher ēK) then the image will be warmer redder to compensate for the cooler temp/light.

If you balance to a warmer (lower ēK) then the image would be bluer cooler to compensate for the warmer temp/light.

Yes it may seem backwards. It is like in the darkroom with negative film, if an print is to magenta, add magenta in the enlarger head, to remove cast. Seems backwards, but it is right.
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Old December 29th, 2009, 10:26 AM   #3
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Yes. That is my understanding, that you are using the Warm (or grey card from stills photography) to "trick" the sensor into shifting WB to where you want it. If you tell it "this cool thing is neutral (or white)" the camera will compensate to warm it up.

But adjusting the WB on the camera directly, as the presenter did on the blog, should have cooled down the image, not warmed it up. Unless he explained it backwards.

I'm overthinking this! Sorry.
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Old December 29th, 2009, 11:21 AM   #4
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You are overthinking it. When you change the temperature, you are not telling the camera what temperature you want. You are telling the camera what temperature the existing light *is*.

So when you change the setting from 5000 to 6000, what you are telling the camera is that the temperature of the existing light is getting blue, so that by raising the setting you are intending to compensate by moving it toward yellow and red.

We intuitively think of blue as a cool color (snowy landscapes on a cloudy day), and red as a color with heat and warmth (marshmellows roasting over the fire), but in the spectrum of light, and the measurement of color temperatures, blue light is hotter than red. Blue is thus actually the warmer color. With paradoxes like this, it's easy to overthink it.
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Old December 29th, 2009, 12:11 PM   #5
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Thank you Tom and Olof.
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Old December 29th, 2009, 02:46 PM   #6
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My take

I always try to simplify this.

In general terms, when you are manually white balancing, the camera is balancing the amount of red and blue light at the scene to achieve a "proper" white color. (Actually it is a RGB balance - but green is not important for this). So when you are outdoors and the scene is about 6000k and therefore has a lot of blue light - the camera adds red to get a "proper" white balance. And when you are at a low light, redder scene at 3000k, the camera adds blue to achieve a "proper" white.

When you are trying to "warm" or "cool" a scene, it doesn't matter so much where you are at on the kelvin scale with your proper white. It is about how far off you are from that proper white. So if you trick the camera into thinking there is more blue in the scene - this is what warm cards do - then the camera adds red to the picture and that makes it look warmer.

So, yes, if the "proper" white is 5600k, then 6600K should look warmer and 4600k should look cooler. My experience with the EX1 tells me that small increments - less then 500k - of difference seem harder to percieve then what I was used to with my SD betacam.

So you do have the scale right, it's just what the camera is doing with it. I'm guessing you're thinking wrong with your Nikon. If you take it out on a cloudy day and set it to the preset tungsten, it should be very, very blue. But, if you are inside in dim lights, the "proper" white could easily be 2800k or below, so the preset at 3200k would warm the scene.
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