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    fletch's Avatar
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    Default Does white balance affect exposure.

    An interesting question came out of this thread about how expsoure is afected by white balance, or isn't.

    So what do you think? Is it?
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    i dont see how WB directly effects the exposure triangle.
    it does effect colour cast tho'
    IMHO they are totally different topics.

    a pedantic approach could be that a lower Kelvin number (which WB is based on) may add a darker "look" because its colder,
    but its an illusion of darkness not an actual difference in light recorded by the sensor.

    as i understand it, Colour temperature is an in-camera HUE adjustment, not an increase or decrease in light.

    i'd be glad to lend an ear to an explaination tho'
    If someone says it DOES effect exposure.. I’d love to see an example of how many EV could be gained through the use of a different Kelvin number.
    (I say that humbly, not in a cocky way)

    I don’t think the two are directly related.
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    Correct white balance ensures that whites end up as true whites in an image-If this is so,18% grey must also be correct-your basis for correct exposure. Don't lose sight of the fact that you camera meter reads light reflected from subjects,and different tones reflect differently- so if say you were using tungsten White balance,you would get a different exposure reading than if you used daylight white balance, because of the different tonality of the light reflected from the subject regards, Ken
    Last edited by kencaleno; 05-12-2009 at 11:00 PM.

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    Quote Originally Posted by kencaleno View Post
    Correct white balance ensures that whites end up as true whites in an image-If this is so,18% grey must also be correct-your basis for correct exposure. Don't lose sight of the fact that you camera meter reads light reflected from subjects,and different tones reflect differently- so if say you were using tungsten White balance,you would get a different exposure reading than if you used daylight white balance, because of the different tonality of the light reflected from the subject regards, Ken
    Ken -- I don't think this can be right. For example, a raw file records "raw" sensor data with no white balance applied at all (stored only as metadata) -- you can completely change the white balance in your favorite raw converter. White balance is applied only after the exposure has been determined, so at least in the way you are mentioning, it shouldn't affect anything.
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    RexK_Cozumel is offline dPS +1000 Club
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    Actually I am with Ken on this one. If you adjust the white balance in ACR after the image is taken and then apply a auto levels or auto exposure adjustment you will see that the program will alter the settings.
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    Quote Originally Posted by kencaleno View Post
    Correct white balance ensures that whites end up as true whites in an image-If this is so,18% grey must also be correct-your basis for correct exposure. Don't lose sight of the fact that you camera meter reads light reflected from subjects,and different tones reflect differently- so if say you were using tungsten White balance,you would get a different exposure reading than if you used daylight white balance, because of the different tonality of the light reflected from the subject regards, Ken
    So, just to clarify.
    Are you saying if I use “Daylight” as opposed to “Tungsten” (or whatever) while the camera is on a tripod, pointed at the exact same subject, on the exact same Aperture, shutterspeed and ISo settings.. the in-camera exposure meter will move when I change the WB? Even if its ever so slightly…
    Are you saying it will be less then 1/3 EV ? (which is the increments on my camera)

    I do agree that different tones reflect light differently. I’m Happy there,
    Digital WB is done after the exposure is taken, its merely an algorithm in the cameras brain. (I’m talking producing an in-camera jpeg from the Raw)

    Film exposure however, (I have no experience with film.. so I’ll leave this bit open ended)
    could exposure be effected by the WB correction because there is a physical colour filter between the subject and the film. Thus interfering with the light.
    or is WB primarily a darkroom thing with film?

    I’ll need to experiment with this.
    Interesting topic tho’


    Quote Originally Posted by RexK_Cozumel View Post
    Actually I am with Ken on this one. If you adjust the white balance in ACR after the image is taken and then apply a auto levels or auto exposure adjustment you will see that the program will alter the settings.
    hmmm.. nice point. i dont use autolevels so never noticed that..
    *ponders*
    Last edited by candleman; 05-12-2009 at 11:45 PM.
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    RexK_Cozumel is offline dPS +1000 Club
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    I dont really use auto levels either in my workflow however I have used it before playing around. Now that I think of it I have probably used every tool in photoshop just playing around. The first thing I do when I get a new version of photoshop is check out the Whats New section and play with all the new stuff
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    Quote Originally Posted by fletch View Post
    So what do you think? Is it?
    It depends on what you mean by "exposure" and on what you mean by "white balance".

    Technically, "exposure" is the process of exposing the film/sensor to the image. It consists of an aperture setting and a shutter speed setting. f/4 is f/4 regardless of white balance or anything else. 1/200 is 1/200 regardless of white balance or anything else.

    Some people use the word "exposure" to mean "in-camera metering". On DSLRs, in-camera metering is not affected by the in-camera white balance setting as it is picked up by separate metering sensors. (I don't know if maybe some of the new-generation live-view DSLRs can do metering from the sensor image, in which case white balance might be involved.)

    However, if you use the word "white balance" to mean the color of the lighting then there can be a small effect on in-camera metering. Nikon uses full-color metering sensors, while Canon uses monochrome "silicon blue cells" that generally do a pretty good job of providing even response across the visible light spectrum. I can't speak for other camera brands. The camera makers try to keep the in-camera metering from being affected by the color of the scene/lighting, but perfection eludes them.

    Some people use the word "exposure" to mean "desired brightness in the JPEG result". In this case the white balance process could conceivably shift the overall JPEG image brightness, depending on the color of the lighting, the colors in the scene, and the selection of white balance adjustment. In practice, the white balance adjustment is designed to have little effect for normal scenes. But again, perfection eludes us.

    Some people use the in-camera histogram to determine if they need to adjust the exposure settings. In most cases, the in-camera white balance adjustment does affect the in-camera histogram. That could cause the photographer to choose slightly different exposure settings for the same scene.

    For some people, the desired exposure for Raw files is "as far to the right as possible". In-camera white balance is not applicable to Raw. The color of the lighting on the scene could affect how far to the right the photographer can safely expose, because the red, green, and blue sensor elements are not equally sensitive nor will they factor equally in the resulting image after Raw developing is done with a particular white balance setting.

    So the overall answer is, "No, not really." There are a number of cases where there could be some minor differences depending on what you mean by "exposure" and by "white balance", but the differences are small enough to be ignored.

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    Egads! You have completely managed to confuse me.

    Per the previous thread I suggested that WB was not part of the exposure (triangle) equation mainly on the basis that for raw files, Wb is completely disregarded. I understand it's an integral part of your finished photo, whether that process occurs in camera to produce a jpg or after the fact in your choice of computer software.

    But when you meter for correct exposure, WB does not play a part or possibly does not play a significant enough part to concern myself with it. So is this line of reasoning correct?
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    Quote Originally Posted by RexK_Cozumel View Post
    Actually I am with Ken on this one. If you adjust the white balance in ACR after the image is taken and then apply a auto levels or auto exposure adjustment you will see that the program will alter the settings.
    Here's the definition of exposure which I am using: the combination of shutter speed, aperture, and ISO which was used when creating the photo. That is all -- and I believe that that is the standard technical meaning. Sometimes it is used casually to refer to the overall level of brightness, but that is casual and not the actual meaning.

    So, using the definition above, changing the color balance does not change the exposure. Applying an auto levels or auto exposure adjustment is indeed post-processing, and does not change your shutter speed, aperture, or ISO -- nothing can change those once you have taken the photo, whether raw or not.
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