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Old Jan 5, 2004, 9:00 AM   #1
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Default Consistent white balance...

Iīve got a problem that I really donīt understand and that I hope that someone could help me resolve...

I want highest possible predictability concerning white balance and color casts. I take portraits and group pictures of about 120 people a day with studio flashes and want every picture to have the same color settings. A grey card or a white paper should be neutral with no color cast.

To achieve this I thought the best way would be to set the white balance manually on my Fujifilm S2 camera, since my thougt is that using the auto white balance mode would mean that a grey card or a white surface COULD have different color casts depending on the color of the subject. This since I guess that the auto white balance mode works that way, analyzing the subject and then applying a new white balance for every new exposure.

So I thought that manual white balance would mean that when you set the white balance with a grey card or a white paper in the ligthing conditions you are going to work in, the result would be that the grey card or white paper should be set to a predefined color cast (or rather no cast, since it shuld be neutral).

So I tried by doing this:

1.
- I set the white balance against a grey card in daylight.
- Then i took a picture of the grey card and a white paper.

2.
- I set the white balance against a grey card indoors with incandescent light.
- Then i took a picture of the grey card and a white paper.

I thought that the result of this would be two pictures of graycards and white papers with the same color cast, but the color cast differed a lot between the two pictures.

Why is this? And if it is like this, what is the idea of using manual white balance since the results are not predictable? Or have I misunderstood how it works?

Regards,
Samuel Rhedin
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Old Jan 5, 2004, 9:39 AM   #2
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It isn't a function of surrounding colors. White balance is a function of color temperature, which is just a fancy way of measure the quality of light, based on the ratio of blue light and red light while ignoring the green light.

Digital cameras usually have built-in sensors to measure the current color temperature and use an algorithm to process the image so that the final result may be close to what we see (with our eyes, of course). But, the algorithm(s) being used may not be accurate enough to make every situation correct. Under some difficult situations when the in-camera algorithm is not able to set the color temperature correctly or when some creative and special effects are needed, we can instruct the camera to use a particular color temperature to fulfill our need. This adjustment that makes sure the white color we view directly will also appear white in the image is referred to as white balance. Setting white balance incorrectly may cause a color shift in the image. For example, suppose the camera is told to use a color temperature of sunlight to take an image of an indoor environment illuminated mainly by incandescent lights. The camera will expect excessive blue light and less red light, and set its algorithm to be more sensitive to the blue light. However, in an environment illuminated with incandescent lights, color temperature is low with excessive red light rather than the blue one. As a result, we shall see a reddish or yellowish image. On the other hand, suppose we set the camera to a low color temperature (e.g., that of incandescent light) and take a photo under sunlight. Because the white balance is set to incandescent light, the processing algorithm is more sensitive to the red light rather than the blue one.


This is why the camera doesn't have just one balance choice, but gives you several options. The auto function works well in many cases, but fails in the more difficult situations. The manual white balance, from my understanding, gives you the ability to shoot a picture of a white card, filling the area in the viewfinder covered by the metering system, then use that image to set the white balance. As long as you are using the same lighting conditions that you set for THAT image, the resulting images should share the same white balance (provided the light quality has not been altered)
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Old Jan 5, 2004, 9:50 AM   #3
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Auto white balance tries to work out what kind of lighting the camera is operating under and then adjusts the camera accordingly.

Manual white balance is typically pre-sets on the camera for daylight (sunny), daylight (cloudy), daylight (shade), incandesant light, flourecent light and flash.

The whole idea being that our eyes can adjust to a variety of lighting conditions that cameras cant, and that as a result in the above situations the light will look different to the camera. For example a red cast on photos taken under light bulbs (incandesant).

How well the camera will adjust automatically or how good the pre-sets will be depends on the camera.

Similarly, some post processing software will allow you to adjust colour temparature in the final image.

Hope this helps.

Regards,
Graham.
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Old Jan 5, 2004, 10:07 AM   #4
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I was assuming that he was referring to the settings that one could adjust in the camera settings, not the pre-sets.
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Old Jan 5, 2004, 10:19 AM   #5
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Thanks for your answers.

But I still donīt understand why the pictures i took doesnīt match. They were shot with manual/custom whitebalance, and you would expect pictures were the greycard was neutral or at least it should have the same color cast in both pictures...

Samuel
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Old Jan 5, 2004, 10:39 AM   #6
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Quote:
Originally Posted by Kidumla
But I still donīt understand why the pictures i took doesnīt match. They were shot with manual/custom whitebalance, and you would expect pictures were the greycard was neutral or at least it should have the same color cast in both pictures...

If I'm reading your comments correctly, you're taking two different pictures with two different light sources. Unless you calibrate the balance for each condition, they won't match.

This is for a Canon DRebel, but your method should be similar:

1. With the mode dial in any setting in the creative zone (M, Tv, Av, P) and the white balance set to any setting, photograph a white subject that fills the metering point ( 9% area in the middle of the viewfinder covered by the partial metering)

2. Press MENU, display the shooting tab, highlight CUSTOM WB and press SET to display the image you took in step 1 and the prompt "select an image"

3. Press SET to use the image to set white balance, or turn the Main Dial to display another picture first

4. Press the MENU or shutter button to exit the menu.

5. Select the icon for custom white balance.

6. When finished taking pictures (under THOSE lighting conditions), reset the white balance mode to auto.


All pictures taken after setting your white balance should attempt to balance to the custom white balance you set. If you change light sources, you will get unexpected color casts.

Hope this helps.
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Old Jan 5, 2004, 10:46 AM   #7
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Thanks again. But as I wrote in my original message I did a new manual white balance setting according to the ligthing conditions, so my point is that the result should match, but it doesnīt!

/Samuel
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Old Jan 5, 2004, 10:47 AM   #8
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Professional studio photographers shoot a gray card under the lighting conditions to be used for their portraits. This is used later as a reference point for your software - i.e. Photoshop. You take your picture of the gray card, click on the eydropper in Levels adjustment and you have the gray value used for your portrait shots. Save and apply it to each image you edit and there should be no white balance problems.

This same technique can be used for indoor, outdoor, available light or flash photos. It does help the camera to produce more properly white balanced photos but the real "magic" is done in your software after capture. Another reason to shoot raw whenever possible.

-Steve
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Old Jan 5, 2004, 11:47 AM   #9
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Steve is right, it is best to shoot raw and adjust afterwards.
If your let the camera select the color temperature and make other adjustments you are stuck with it or have to spend time trying to undo odd color casts.

You can also try a digital camera profiler like the QP colorkit 1 from www.adi-digital.com They give you a color refrence card you shoot first under each type of lighting before your do your shoot. Then their software analyzes the shot and applies correction to all the other images you made at that time.
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Old Jan 5, 2004, 12:19 PM   #10
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While I agree that adjusting white balance in the digital darkroom will yield better results, it should follow reason that once you set your white balance to the conditions you're shooting using the custom white balance option (not the presets), you should get a set of photos that all render the same white balance (when shot under identical color temperature conditions) which will allow you to do a batch adjustment to the entire group and receive very close results. It is not feasible to adjust every shot you take individually when you're shooting over 100 images.

With regards to Samuel's original comments, the only thing that I can figure is that a) you didn't set the white balance correctly per your camera's instructions, or b) your lighting color temperature is not constant between shots (moving the light source, altering the intensity, etc). or c) I am clueless regarding this issue and it isn't possible. :lol:
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