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DPChallenge Forums >> Tips, Tricks, and Q&A >> Using custom white balance
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12/13/2006 10:35:36 PM · #1
Hi,

I was wondering if someone might be able to point me towards a tutorial or thread related to how custom white balance works. I know that if I shoot in raw I can set WB later, but I'm not quite there yet. I'm mainly interested in what kind of quirky effects I can get straight out of the camera (and not just setting the right "white") as well as setting WB for stuff like infrared photography (though I have found some tutorials on that). So if anyone could point me in the right direction, or even give me a quick crash course, it would be greatly appreciated. Thanks!
12/13/2006 11:38:39 PM · #2
Custom WB works like this; you take a shot of something white then open the "custom WB" option on the menu, select the shot, and it will set white balance to make that true white.

If you want to set it for quirky results, point the camera at something not-white (like red, or blue, or green, whatever) and then set the custom WB off that. If you set WB off a red shot, then the WB will remove red from your image by shifting towards cyan, basically. Use a color wheel to see what the opposites are. If you have a certain color you want to shift towards, find its opposite on the color wheel and shoot something of that approximate color to do your custom WB from.

That's it in a nutshell, though I have never really messed with this at all.

R.
12/14/2006 10:21:17 AM · #3
Originally posted by Bear_Music:

If you set WB off a red shot, then the WB will remove red from your image by shifting towards cyan, basically. Use a color wheel to see what the opposites are. If you have a certain color you want to shift towards, find its opposite on the color wheel and shoot something of that approximate color to do your custom WB from.
R.


Awesome. Thanks a lot! Short and simple. It's still a bit confusing for me, but now I know where to concentrate my efforts. I've found a good color wheel at //www.photocourse.com/itext/RGB/ and I'm slowly starting to understand things a little better.

On the other hand, you mention that to remove red from the shot, set WB off a red shot. Also, if I wanted to shift towards red, I would set WB off the opposite color. And the confusion comes in here: If I'm shooting infrared, which comes out all red, why am I setting WB with green? From what I understand I want to remove red (is this analogous to saying that I want to shift towards green?) - and this would lead me to believe that I would set WB with something red.

But slowly and surely, I'll make my way there. Once again, thanks a lot!
12/14/2006 10:39:14 AM · #4
Maybe this will help, each colour pair in this chart are the opposites in terms of white balance. Custom white balance on one, add a colour cast of the opposite pair to the final image. I used to use this card in place of carrying filters when out shooting.



Message edited by author 2006-12-14 10:40:38.
12/14/2006 12:21:32 PM · #5
Originally posted by Gordon:

Custom white balance on one, add a colour cast of the opposite pair to the final image.


Cool. Thanks! Things are slowly getting put together in my mind. Still, though, there is some confusion. It's one of those instances where I know I'm close, but I'm missing a key bit of knowledge that will allow me to further understand the concept. (and of course, once I get it, it'll be "ahh, that's soo simple, why didn't I understand this before?")

And here's why: I'll use the example of infrared once again. The goal, from my understanding, is to remove the red color cast from the photo. I see that red and green are opposites on the chart - so if I custom on green, I will be adding a red cast. But this is opposite to what's supposed to be happening. Shouldn't I be setting on red in order to add a green color cast to the image?

12/14/2006 01:16:03 PM · #6
Originally posted by Dudski:

[quote=Gordon]
And here's why: I'll use the example of infrared once again. The goal, from my understanding, is to remove the red color cast from the photo. I see that red and green are opposites on the chart - so if I custom on green, I will be adding a red cast. But this is opposite to what's supposed to be happening. Shouldn't I be setting on red in order to add a green color cast to the image?


The custom WB will neutralize whatever color it is set on to white, basically. It takes the frame you just shot and sets a WB to make the frame neutral white. The basic discussion was "how to remove a color cast with custom WB" — to do this, you shoot a white card in the light you will be using with the camera settings you will be using (except auto WB) and then use that shot to set the cutom WB, and whatever color cast was on the white card will be eliminated. In practical terms, this means the custom WB adds a cyan shift if the card showed a red color cast.

See how it works? If you want a NEUTRAL image (no color shift) you use a WHITE card and let the camera do the work. No need to worry about what color card to use.

The secondary discussion was "How do I set an intentional color shift away from neutral?" This assumes you are using a process that, if unmanipulated, would give neutral color; for example, an outdoor scene in midday sunlight. If you exposed the white card in these conditions, and used AWB, the custom WB would not change the auto WB. Now, if in these conditions, and for a normal image, you exposed a RED card and used this exposure to set your custom WB, then the camera assumes that the red card was actually a white card, and it programs in a cyan shift to neutralize that red, see? So when you shoot the actual landsacpe (which is NOT red) using that custom WB, it would come out with a pronounced cyan shift.

How all this relates to what you are doing with infrared filters I don't really know, as I've never done that in digital. But I'd assume, whatever process you're using, if your goal is to take a truly neutral image then you use a white card to set CWB. And if you want a color shifted image, then you use the card of the complementary color to the shift you desire. Exactly as described above. The only thing is, if the IR filter/process you're using makes a pronounced red shift, and you want to not only neutralize that and introduce a cyan shift, it's at least conceivable the shift is outside the camera's gamut. I really don't know.

R.

Message edited by author 2006-12-14 13:18:45.
12/17/2006 10:45:22 PM · #7
Just wanted to say thanks guys for the help! I've been putsin around with the camera and with the info things are starting to make sense. So once again, thanks!

Damian
12/21/2006 11:25:41 PM · #8
At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?
12/21/2006 11:30:49 PM · #9
Originally posted by zheka:

At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?


Auto is actually best.

R.
12/21/2006 11:40:32 PM · #10
Originally posted by Bear_Music:

Originally posted by zheka:

At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?


Auto is actually best.

R.


I seem to get better results when I do a custom white balance when the light source isn't changing.. The auto white balance always comes out too yellow..
12/21/2006 11:47:41 PM · #11
What about just shooting RAW? You can then deal with the white balance after the fact. I did do a lot of custom white balance before with my P&S camera. What I did was just carry around a white note card and used that to set the white balance.
12/21/2006 11:49:59 PM · #12
Adding example pictures here for backing up my previous statement:


auto white balance.

and


custom white balance.
12/21/2006 11:50:33 PM · #13
Originally posted by SamDoe1:

What about just shooting RAW? You can then deal with the white balance after the fact. I did do a lot of custom white balance before with my P&S camera. What I did was just carry around a white note card and used that to set the white balance.


That's been suggested, by me and others, but the issue here is simply; "How do I set a custom WB in my camera?"

R.
12/21/2006 11:52:38 PM · #14
I recently purchased a expodisc for just this purpose and it works great! You simply put it on the end of your lens like a filter and shoot from where your subject will be, pointing the lens back at where you'll be shooting from. Then set that image as your custom WB image, set WB to custom and remove the disc. Then you shoot away. Got rid of the yellow cast I was always picking up on my indoor shots. Works just as well outdoors too.
12/21/2006 11:53:55 PM · #15
Originally posted by jfriesen:

Originally posted by Bear_Music:

Originally posted by zheka:

At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?


Auto is actually best.

R.


I seem to get better results when I do a custom white balance when the light source isn't changing.. The auto white balance always comes out too yellow..


The question was, "When shooting a white card to use in setting custom WB in-camera, what WB should I be using to shoot the card?" I'm niot proposing that Auto WB is a better solution than Custom WB for shooting in atypical light; I'm saying Auto WB works fine for exposing the card to set your Custom WB off of.

I agree with you that Auto WB doesn't work as well as you'd like it to sometimes, especially (in my experience) under tungsten lighting, and setting tungsten or custom WB works better for JPGs.

R.
12/21/2006 11:55:24 PM · #16
the expodisc replaces the need for white and gray cards
12/21/2006 11:56:53 PM · #17
Originally posted by Bear_Music:


That's been suggested, by me and others, but the issue here is simply; "How do I set a custom WB in my camera?"

R.


Now Bear, we all know you are the photog genius, we're just trying to add our two cents.
01/04/2007 02:58:01 AM · #18
Shooting RAW with an ExpoDisc is an excellent combo actually. It gives you that Custom choice in your RAW converter, it's often the best one and you don't have to play with the WB setting, and if it isn't the best choice, you have the flexibility to change it.

In the brief time I've shot with the ExpoDisc (XMas present from a very generous fellow photog), it seems to make a huge difference over either the Auto or light-specific settings when shooting under artificial lights.

Here's a few quick test shots:

Auto WB
Incandescent WB
ExpoDisc Shot (from the wall pointed up at the overhead light)
Custom WB using ExpoDisc shot

The walls, photo mat and horizontal book are all white in real life. The ExpoDisc really nails it!
01/04/2007 08:45:21 AM · #19
If you don't have an ExpoDisc (they're expensive) try using a white coffee filter, paper napkin, etc. Hold it in front of the lens, turn AF off, and take a shot. Use that to set your WB.
01/04/2007 09:02:39 AM · #20
Originally posted by Bear_Music:

Originally posted by zheka:

At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?


Auto is actually best.

R.


This doesn't make any sense, though it doesn't actually matter.

You can and should be able to shoot the white frame for a custom white balance reference in any white balance mode - the processed result isn't what is used anyway - that's entirely the point. The image is neutralised and that shift used to calculate the white balance adjustment for future shots - the white balance mode used when shooting the white balance reference is entirely irrelevant.

01/04/2007 10:12:34 AM · #21
Originally posted by Gordon:

Originally posted by Bear_Music:

Originally posted by zheka:

At what white balance do you shoot the white card to get the image for the custom white balance? Anything but Auto?


Auto is actually best.

R.


This doesn't make any sense, though it doesn't actually matter.

You can and should be able to shoot the white frame for a custom white balance reference in any white balance mode - the processed result isn't what is used anyway - that's entirely the point. The image is neutralised and that shift used to calculate the white balance adjustment for future shots - the white balance mode used when shooting the white balance reference is entirely irrelevant.


Not entirely; the more correct the test exposure is, the more accurate will be the custom WB, although the differences are small. You are correct that custom WB will work regardless of the setting the test was shot with. My response was to the question "anything but auto", and I commented that actually auto is preferable, not that auto is the only way.

R.

Message edited by author 2007-01-04 10:12:52.
01/04/2007 10:59:41 AM · #22
Originally posted by Bear_Music:


Not entirely; the more correct the test exposure is, the more accurate will be the custom WB, although the differences are small. You are correct that custom WB will work regardless of the setting the test was shot with. My response was to the question "anything but auto", and I commented that actually auto is preferable, not that auto is the only way.

R.


Again that doesn't really make any sense. The white balance doesn't affect the exposure. It also doesn't affect the white balance information captured to evaluate the custom white balance.

Think about it and you'll realise why its nonsense. Otherwise if you used a tungsten white balance to shoot your custom white balance frame and a sun white balance to shoot your custom white balance frame you'd get a radically different custom white balance.

The fact is, the white balance settings don't matter one jot the calculation is done on the raw captured data, not on the processed information.

In fact the manuals even say that ' Set any white balance setting' this is because its entirely irrelevant to shooting for a custom white balance frame - you just want it exposed correctly. 'Auto' exposure mode might be worth using, but auto white balance doesn't matter, though even there, if you shoot in 'auto' exposure mode, you'll underexpose the card and get an incorrect white balance as a result.

Message edited by author 2007-01-04 11:03:52.
01/04/2007 11:03:30 AM · #23
Originally posted by Gordon:

The fact is, the white balance settings don't matter one jot the calculation is done on the raw captured data, not on the processed information.


You would think that were so. It makes perfect sense. However, it has been my observation (and others, for that matter) that there IS a slight difference. I have no idea why. Maybe things have changed; I did this testing years ago. I won't debate it any further; I'll yield to your expertise.

R.
01/04/2007 11:08:06 AM · #24
Originally posted by Bear_Music:

You would think that were so. It makes perfect sense. However, it has been my observation (and others, for that matter) that there IS a slight difference. I have no idea why. Maybe things have changed; I did this testing years ago. I won't debate it any further; I'll yield to your expertise.

R.


Variance in exposure and lighting of the test subject will vary the custom white balance. So poor or inconsistent testing is likely to be to blame.

I've read the algorithms used to do these sorts of calculations, reference frame white balance is not a factor in any way, shape or form. Maybe its different in Canon SLRs - I haven't read their code. However, they state pretty straightforwardly in the manual that it has no affect and to use any white balance you like.

Message edited by author 2007-01-04 11:10:23.
01/04/2007 11:34:22 AM · #25
Gordon: Thanks very much for explaining that the processed image isn't what's used for the custom WB shift, it's the raw data.

That explains why, in my test, the wall looks white regardless of whether I shot the ExpoDisc reference shot using Auto WB or a previous custom WB I had, even though the resulting processed images look so different.

ExpoDisc shot using "Auto WB"
Resulting shot using above file
ExpoDisc shot using a previous "Custom WB"
Resulting shot using above file

The WB of the 2 resulting shots is identical (thumbs may look a tiny bit different).

I couldn't figure out how such differently colored reference images could both produce the same result, but the explanation makes sense and looking at the above results, it really doesn't matter what WB setting the camera is on when you take the ExpoDisc (or equivalent) shot.

But since the processed reference image is a JPEG, how is it that the camera is able to strip the data down to the raw info? I would have thought that once it was a JPEG a lot of that data would have been lost (or entombed).

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