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08-02-2010, 08:35 PM - 1 Like   #1
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Help Me Understand White Balance

Cause I've read tons of online stuff, as well as a book, on white balance, and I still don't really get the concept. I understand (or think I do) that when you take a sample picture for the camera to determine white balance (I used a blank sheet of printer paper), the camera uses that as its basis for what is white and configures the color balance accordingly. When I tried that, however, my indoor pics turned out much yellower than they should be.

On the whole, I just don't think I get the concept overall, and it does seem a bit niggling that I leave this on auto while I have a firm grasp of doing everything else in manual. Thanks for your help!

08-02-2010, 11:15 PM   #2
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You are probably having trouble because you are making it harder for yourself than it is.


Your brain lies to you, the camera doesn't

The basic fact is this: Light comes in different colors. This is true apart from photography, but we tend not to notice it, because our minds automatically adjust. We don't notice that colors look different in florescent light than in normal sunlight. In the same way, we tend not to notice how sloppy somebody looks or how messy the room we're standing in really is. We tune these things out normally.

Until we take a photograph. Because the camera does NOT tune things out. It doesn't clean up the room or tuck your friend's shirt in for him. And it doesn't automatically adjust the color of the light. If your camera is set to expect normal sunlight, and you shoot a photo inside at night using the light of a normal tungsten lamp, well, the colors are probably going to look "wrong."


Try it for yourself

The best way to understand this is simply to see it for yourself.

Open a book with white pages under a lamp in your living room at night. Set your camera's white balance to something inappropriate, like sunlight. Take a photo. Look at the photo on the camera's display screen. What you see won't be pretty. The white pages of the book may look orange-ish—or perhaps it will seem more yellow or more red to you, depending on your light, the actual whiteness of the book, and other factors. Anyway, it will look awful.

Now, change the in-camera WB setting to tungsten light, and take another photo. This time the white pages of the book will probably look much better, much more like what you actually see.

Finally, change the in-camera WB setting to AUTO and take a third photo. This time the photo may look even more like what you THINK you see, that is, the white page may look downright white.

At least those are the results I got just now when I did this same experiment here. On auto, the camera was actually overcompensating a little bit.

Which of the three photos is best? Well, it's probably not the one where the white balance was set wrong, to sunlight, although occasionally photographers have been known to deliberately do this sort of thing in order to achieve a special effect—say, to give a warmer appearance to a scene. The photo you will like best is probably one of the other two. Why can't we say for sure which is best? Because our minds continue to compensate even when we look at the photo on our computers (or in print).


Shoot raw + AWB and worry no more

Want to stop thinking hard about white balance? It's easy to do. Two steps:
  1. Set your camera to shoot raw.
  2. Set the camera's WB setting to Auto.
If you shoot on auto white balance, the camera will calculate what it thinks the right white balance to be and embed that info in the picture file. When you open the raw file on your computer, your software (Lightroom, Photoshop, whatever) will accept the camera's guess about the right white balance and display the photo that way. My Pentax DSLRs are generally VERY good at getting the white balance right in auto.

And if you shoot raw and the camera's guess about the white balance doesn't strike you as quite right, you have all the data necessary to modify the white balance after the fact. If you shoot jpeg, on the other hand, while you can adjust the white balance on your computer you won't have nearly the same latitude to do so as you would if you shot raw.


Two final comments

First, although white balance seems largely a digital problem, but actually, the color of light was a problem back in the film days, too. Different types of film were better suited to different types of light.

The other comment is that white balance can become a very difficult problem indeed when there are mixed light sources, say, some daylight, some light from a bright tungsten lamp, perhaps some florescent light thrown in there for good measure, and (gack) the light from a flash. This is when you will want to convert the photo to black and white. ;-)

Will
08-03-2010, 02:47 AM - 1 Like   #3
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Will has giving an extensive outline of why white balance is an issue you need to care about.

A few more things:

- The colour white (is it a colour?) is expressed in temperature Kelvin. Coming from the radiation of a black body emitting light when heathed to a certain temperature.
- Some software will enable you to change the white balance setting by you pointing a point in the picture that is supposed to be white
- RAW pictures contain raw sensor data *without* any in camera processing, but it includes camera settings (like colour temperature) in the file stored.
- RAW pictures can easlity be altered to *any* colour temperature, that's the main reason why I only shoot RAW.
- Since RAW pictures are not post processed by the camera, you will need to do: sharpning, noise reduction, etc. in post processing as well. I use Lightroom for that.
- Lightroom can apply standard profiles to pictures while importing files to automate that process, and a lot more....
- No, I do not have Adobe shares.

Success, Bert
08-03-2010, 03:23 AM   #4
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I am also new to photography so i have taken an interest in this thread and i have noticed in a few places of people talking about 18% grey.

1 How is this different to AWB.

2 Is it possible to manually preset AWB by taking a sheet of white paper/ 18% grey on a shoot and setting onsite. As i work alot with CCTV cameras and this is always done onsite but was unsure if this could be done with a DSLR

08-03-2010, 06:03 AM   #5
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QuoteOriginally posted by Grazy81 Quote
I am also new to photography so i have taken an interest in this thread and i have noticed in a few places of people talking about 18% grey.

1 How is this different to AWB.

2 Is it possible to manually preset AWB by taking a sheet of white paper/ 18% grey on a shoot and setting onsite. As i work alot with CCTV cameras and this is always done onsite but was unsure if this could be done with a DSLR
18% grey has to do with proper exposure--not proper color affected by WB settings.

Your camera (all cameras, basically) uses 18% grey as the middle of the entire tonal range. No, it's not 50, and don't ask me why. So...

For this lesson, let's NOT use a metering mode which averages all of the values in a scene, everything you see in your viewfinder. Instead, we're using metering methods which only "read" and react to the elements in the scene YOU decide.

Let's go:

You have a person wearing a black shirt, white pants, standing against a really dark red wall. What does your camera meter for (F stop and shutter speed) to get the best exposure for these different percentages of grey?

And yes--white is 0% grey, black is 100% grey, and that red wall might be 70% grey.

Anyway, let's assume you used your spot meter (but don't) or center-weighted meter, and only metered for the white shirt. The camera thinks that the shirt is 18% grey, and adjusts its settings accordingly--which means the shirt will come out 18% grey in your final picture! And the other elements will be way underexposed!!!


But if you spot metered off an actual 18% grey card, everything in the scene would be properly exposed. (Within reason. This can get more complicated, but for now, this is enough.)

So when you use center-weighted metering in your camera, you have to be aware exactly WHAT element in the scene you're using as the basis for your final exposure, because that element may be far off 18% grey--plus, its percentage of grey may be so drastically off as to affect other elements in your picture.

Such as this example:

If I'm shooting a single, solitary tree in a big field and I'm real close to the tree and using center-weighted or spot, the camera is going to more or less expose properly for the brown of the tree, because it's near 18% grey--but the grass in the background may be overexposed because that light green is a lighter percentage of grey. (Again, don't mess with Spot metering yet.)

It's just something to understand as you first start out, and as you shoot more and more, you'll understand why shots you think should have been exposed correctly didn't come out way. And you'll get the hang of using AE lock to lock your exposure, or compensation, to get exactly what you want.

Basically, the camera doesn't know exactly which part of the scene you want perfectly exposed. You have to tell it.

Hope I'm explaining it right.

Last edited by Ira; 08-03-2010 at 06:28 AM.
08-03-2010, 06:39 AM   #6
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QuoteOriginally posted by Grazy81 Quote

2 Is it possible to manually preset AWB by taking a sheet of white paper/ 18% grey on a shoot and setting onsite.
To answer the question more succinctly; no, it is not possible to manually set Auto White Balance (AWB). If you set it manually, then it is, by definition, not auto.
08-03-2010, 06:45 AM   #7
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White paper? White paper? I've got 5 sheets of "white" paper in front of me and none are the same. One looks grayish. Another is bluish. The bluish one is the brightest of the 5. Why is it blue you ask? Simple really. In a quality paper to get brightness high they bleach it with titanium oxide. It makes it a bright white. But alas it's expensive and only the higher grade paper mills do it. By adding a tinge of blue however they can get that brightnesss number higher. But it's not really white. What's all this have to do with white balance? Simple. White is not white. An 18% gray card is exactly that. It's calibrated to 18% gray. However exposure to light will change the color of it. My Pantone books (printer's color guides) have the same problem. So it is recommended that for the critical color jobs you get new ones every 12 months. And they are by no means inexpensive. Over $100 for the main book.
08-03-2010, 07:26 AM   #8
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This talk about something called "white paper" threatens to completely confuse the issue.

White balance is not about the inherent color (if there were such a thing) of "white paper" or "18% gray paper". White balance is about THE COLOR OF THE LIGHT that's floating around illuminating the scene. It's about the color of the light that bounces off that putatively white piece of paper and hits your camera's sensor.

As I said in my initial response, the light floating around illuminating your scene has a color to it. And as the light bounces off various colored objects in your scene, it causes those objects to appear tinted one way or another. Why don't we SEE this ourselves? Thank God that we don't! If we did, then the color of everything in our lives would appear to change constantly as the light changes—as we move from room to room, whenever we turn on a lamp or an overhead light. After a swim in the middle of a sunny day, you put on a "white" tee shirt, but when you walk back to your house, it changes color as you walk into the shade of a tree, or if a cloud blocks the sun, and it really changes color when you step out of the sunlight into your kitchen and the shirt is now illuminated by the florescent light fixture on the kitchen ceiling. This would drive us crazy. So our brains are hard-wired to provide a kind of automatic color balance. This allows us to perceive the shirt as having a constant color all day long.

White balance in photography simply tries to do the same thing: allow objects in photos to appear to be the colors that we perceive them to be.

Now, if there happens to be a piece of "white paper" in your photo—or if you deliberately take a photo of a piece of white paper—and you save your photo as a raw file, then LATER ON, ON THE COMPUTER you may be able to use that item in the photo to adjust and correct the photo's white balance. But what you are doing in this case is allowing the "white paper" to reflect the light whose color you might want to adjust and/or correct.

*

As for the 18% gray card, first, while in fact you might be able to use a gray card to help with white balance, the main reason photographers have carried and used gray cards in the past is for exposure, NOT for white balance. And second, what matters here isn't the color gray. It's the 18% part that really matters. Apparently a card that is 18% gray reflects about half the light that hits it (absorbing the other half). In other words, the card represents a medium between absolutely pitch black (which in theory reflects no light) and pure white (which in theory reflects all the light that hits it). The medium-gray card matters because it's medium, not because it's gray. A medium red card could, at least in theory, work just as well.

I'll leave it at that, because to go any further takes us away from the subject of the color of light, and into the subject of exposure.

Will

08-03-2010, 07:52 AM   #9
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From Wikipedia

QuoteQuote:
A major use of gray cards is to provide a standard reference object for exposure determination in photography. A gray card is an (approximate) realisation of a Lambertian scatterer; its apparent brightness (and exposure determination) therefore does not depend on its orientation relative to the light source. By placing a gray card in the scene to be photographed, oriented at a defined angle relative to the direction of the incident light, and taking a reading from it with a reflected light meter, the photographer can be assured of consistent exposures across their photographs. This technique is similar to using an incident meter, as it depends on the illuminance but not the reflectivity of the subject.

In addition to providing a means for measuring exposure, a gray card provides a convenient reference for white balance, or color balance, allowing the camera to compensate for the illuminant color in a scene.

Gray cards can be used for in-camera white balance or post-processing white balance. Many digital cameras have a custom white balance feature. A photo of the gray card is taken and used to set white balace for a sequence of photos. For post-processing white balance, a photo of the gray card in the scene is taken, and the image processing software uses the data from the pixels in the gray card area of the photo to set the white balance point for the whole image.

Most digital cameras do a reasonable job of controlling color. For the casual user, a gray card is unnecessary. Many serious photographers or hobbyists consider gray cards an essential part of the digital photography process.

Gray cards are made of a variety of materials including plastic, paper, and foam. Some photographers hold[citation needed] that any neutral white or gray surface, such as a white piece of paper, a concrete or stone wall, or a white shirt are suitable substitutes for a gray card; however, since bright white papers and clothing washed in typical detergents contain fluorescent whitening agents, they tend to not be very spectrally neutral.[1] Gray cards specially made to be spectrally flat are therefore more suitable to the purpose than surfaces that happen to be available.
A gray card gives you a known reference. It is an exact color. You can use it for exposure and balance. A "white" sheet of paper is an unknown. With a gray card in the first shot I can balance the color for all shots taken at that time under the same circumstances.

Last edited by graphicgr8s; 08-03-2010 at 07:59 AM.
08-03-2010, 08:29 AM   #10
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QuoteOriginally posted by graphicgr8s Quote
A gray card gives you a known reference. It is an exact color. You can use it for exposure and balance.
Yes, you can. Wasn't what the cards were used for back in the days of film, since there was no white balance option on the camera, aside from picking the right film for the environment you were shooting in and/or using filters. But yes, a gray card can be used today for exposure AND white balance, if you want to bother.


QuoteQuote:
A "white" sheet of paper is an unknown. With a gray card in the first shot I can balance the color for all shots taken at that time under the same circumstances.
Well, first, an 18% gray card is known only because it's been manufactured to be 18% gray. If you purchased a 100% white card that had been carefully designed as such, it would be just as fixed a value. Your point is simply that there is a very wide variance in the actual tints of papers and other materials that we think are all "white." Quite true.

*

The word "color" gets used here in a couple of different ways that can be confusing. We talk about the color of objects as if that were an objective fixed thing, and we talk also about the color of light. And then we confuse things even further by talking about the color of light as its TEMPERATURE. And to make matters even worse, when we're talking about light, the lower the temperature, the WARMER the light (or at least that's how we talk about it).

It can be a very confusing subject to talk about.

*

That's why I think it's really useful to shoot raw, put your camera into auto white balance and leave it there, and then fix problems on your computer as they arise. (Calibrate your computer's display, of course.) The ability to stop worrying about white balance almost completely while shooting is, in my opinion, all by itself a sufficient justification for shooting raw all the time.

BUT, before beginners do this, in order to see the PROBLEM of white balance for themselves, they should simply try shooting some jpegs in different kinds of light while playing with the white balance settings. Shoot outside in the full sun at noon on a cloudless day—with the camera's white balance set to cloudy, then again with the white balance set to sunny, and then with the white balance set perhaps to one of the artificial lighting options. Observe the differences in the resulting pictures. Understand that each in-camera setting is basically telling the camera to expect the LIGHT to be a certain color (that is, a certain temperature).

Then put the camera back to raw capture + AWB and be happy.

Will
08-03-2010, 10:44 AM   #11
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Will, you really couldn't use a white card. Your exposures would be all over the place. Think about it. Just as you couldn't use a totally black card.

As for temperature. It's just a matter of whether it leans to the red or the blue. Red being warm (think Fire) Blue being cool (think cool refreshing water)
08-03-2010, 10:59 AM   #12
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QuoteOriginally posted by graphicgr8s Quote
Will, you really couldn't use a white card. Your exposures would be all over the place. Think about it. Just as you couldn't use a totally black card.
Hmm, maybe you're right. I don't use gray cards, either, for color balance OR exposure. And I have an ExpoDisc gathering dust in my studio as well. ;-)


QuoteQuote:
As for temperature. It's just a matter of whether it leans to the red or the blue. Red being warm (think Fire) Blue being cool (think cool refreshing water)
Yeah, but my point was "warm" here is a lower temperature, that is, lower Kelvin number. Candlelight is as "warm" as it gets, but it has a temp of around 1500K—just about the lowest temp we usually give a number to on the scale.

Will
08-03-2010, 12:11 PM   #13
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QuoteOriginally posted by jaieger Quote
I understand (or think I do) that when you take a sample picture for the camera to determine white balance (I used a blank sheet of printer paper), the camera uses that as its basis for what is white and configures the color balance accordingly. When I tried that, however, my indoor pics turned out much yellower than they should be.
Chances are you didn't do this right, then. You can't just take any old picture of a piece of paper to set WB - you have to be in the special manual WB setting mode. You have to make sure the white paper is in the same light as your subject. And then you have to stay in manual WB mode when taking the actual shots.

If that doesn't sort out what went wrong, post one of the pictures with EXIF intact.
08-03-2010, 01:13 PM   #14
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QuoteOriginally posted by WMBP Quote
Hmm, maybe you're right. I don't use gray cards, either, for color balance OR exposure. And I have an ExpoDisc gathering dust in my studio as well. ;-)




Yeah, but my point was "warm" here is a lower temperature, that is, lower Kelvin number. Candlelight is as "warm" as it gets, but it has a temp of around 1500K—just about the lowest temp we usually give a number to on the scale.

Will
I don't use them either. Never have and haven't owned one until I bought Scott Kelby's book and there happened to be one there.

As for color temperature. Most people just starting in photography haven't a clue about color temps. We do because we do this all day long. So in this case I thought a simplistic explanation was in order. I am a lot older now than when I started shooting so I can usually tell where I need to be. Except of course when mad cow hits.

Cheers
George
08-03-2010, 02:19 PM   #15
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QuoteOriginally posted by WMBP Quote
Shoot raw + AWB and worry no more

Want to stop thinking hard about white balance? It's easy to do. Two steps:
  1. Set your camera to shoot raw.
  2. Set the camera's WB setting to Auto.
If you shoot on auto white balance, the camera will calculate what it thinks the right white balance to be and embed that info in the picture file. When you open the raw file on your computer, your software (Lightroom, Photoshop, whatever) will accept the camera's guess about the right white balance and display the photo that way. My Pentax DSLRs are generally VERY good at getting the white balance right in auto.
I agree with shooting RAW to give you much more control. I also find my K-7 has exceptional AWB. However, I would question what the 'right' WB is. I recently heard a top pro say get off AWB and shoot all your outdoors stuff in Daylight WB. You'll get more satisfying colour. You can also use artificial street light etc to really add a feeling of warmth/artificial-ness.

I think this was a good point. AWB can wash out your images by being 'correct' all the time. Of course, you can replicate daylight WB after the fact with RAW, but it's important to have a well-calibrated screen.
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