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  • 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?
    Fletch

    << blog >> - flickr
    Olympus E510 - Ok to edit and re-post on DPS only

  • #2
    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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    • #3
      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, 11:00 PM.

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      • #4
        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.
        David Clark Photography, project 365 photo blog, flickr.
        It is OK to edit and repost my photos on the DPS forums only.

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        • #5
          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.
          Rex K

          The view from my "office" doesn't suck.

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          • #6
            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’


            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, 11:45 PM.
            http://www.flashpointphotography.co.nz/
            D300s | D7000 | D80 | 17-50f/2.8 | 50-150f/2.8 | 24-70f/2.8 | 10-20 f/3.5 | SB910 | SB900 | SB600 | SB28 PhottixStratos

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            • #7
              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
              Rex K

              The view from my "office" doesn't suck.

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              • #8
                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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                • #9
                  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?
                  Mike
                  CloutierPhoto.com
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                  • #10
                    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.
                    David Clark Photography, project 365 photo blog, flickr.
                    It is OK to edit and repost my photos on the DPS forums only.

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                    • #11
                      Yes, it does. And here's why.

                      Digital cameras are, theoretically, infinitely variable. Your aperture is measured in stops, half stops and third stops, but really the camera could set it to 2.3478654 if it wanted to. The same goes for shutter speed. I cant count the amount of times I see the full EXIF of a shot and see 10384/100000s exposures. Sure, that's 1/10, but its not PERFECT

                      Assuming you take a shot at exactly f/8 and 1/200s, and the camera applying white balance modification after the actual exposure, then its entirely possible that the EV resulting be slightly different than exactly that.
                      I am responsible for what I say; not what you understand.
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                      • #12
                        Originally posted by OsmosisStudios View Post
                        Yes, it does. And here's why.

                        Digital cameras are, theoretically, infinitely variable. Your aperture is measured in stops, half stops and third stops, but really the camera could set it to 2.3478654 if it wanted to. The same goes for shutter speed. I cant count the amount of times I see the full EXIF of a shot and see 10384/100000s exposures. Sure, that's 1/10, but its not PERFECT

                        Assuming you take a shot at exactly f/8 and 1/200s, and the camera applying white balance modification after the actual exposure, then its entirely possible that the EV resulting be slightly different than exactly that.
                        Assuming that by "white balance", we mean the setting on a camera which determines the color temperature... This doesn't explain why adjusting the white balance would affect the exposure. If changing the white balance changes the exposure, then there must be a reason. The fact that shutter and aperture are continuous measurements (which is not exactly correct, but close enough) is irrelevant if you can't find an explanation linking exposure and white balance.

                        I believe that I have a solid understanding of the technical aspects of digital photography: how a photo is taken, from sensor to processed jpeg (or to unprocessed raw file), and I understand where both exposure and white balance fall into this process. White balance is totally disconnected from determining the exposure. However I do not claim to have a perfect understanding. If anyone can give me a technical explanation why changing white balance should change exposure, I would be very happy to hear it! I'll gladly eat my words, but so far I have not seen any technical explanation at all.

                        Edited for clarity.
                        Last edited by dcclark; 05-13-2009, 02:20 AM.
                        David Clark Photography, project 365 photo blog, flickr.
                        It is OK to edit and repost my photos on the DPS forums only.

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                        • #13
                          Originally posted by Sixpak View Post
                          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?
                          Again, you need to specify what you mean by "WB". If you mean the camera's WB setting, then there is no effect at all on in-camera metering. The only effect would be on the histogram, which might cause the photographer to choose a different exposure setting.

                          If by "WB" you mean the color of the lighting, then yes the color of the light being metered can have an effect on in-camera metering. However, the camera manufacturers try to reduce that effect as much as possible and generally are quite successful.

                          In any event, as you say, it "does not play a significant enough part to concern myself with it."

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                          • #14
                            The way I see it (and this is entirely untechnical/uneducated) is that the camera WB setting is akin to telling the camera to apply a filter to the data recorded. If the WB setting is considered by the camera pre recording, then it should affect the resulting exposure...

                            I.e. you take two pictures of a light...one WB setting tells the camera the light should be white, the other WB setting tells the camera the light should be "browner"....the second WB setting *should* result in a lower exposure and affect the camera's metering....(the camera would bump the metering/exposure to prevent underexposure)

                            If the WB setting is applied after recording, then it would not affect the camera's metering, but would affect the levels of what is displayed (it's exposure, the second setting would appear underexposed)

                            To my mind exposure is ALWAYS what is recorded...it is determined by settings..Correct exposure is determined by metering.
                            WB is always the "correct" color of light and" filtering" to correct for differences between the way we see things and the "literal" way a camera sees things.

                            If it's a raw file, then it only affects things when you apply them in post.....most programs apply the "settings" to the displayed image even in RAW...they just are not "applied" until saved in conversion.....But try looking at an image in Lightroom or similar...one with no camera settings/profiles applied, and then with "as recorded"....The difference can be striking in many aspects....including apparent exposure.....

                            I say "apparent exposure" because "what" was recorded (the exposure) does not change, but who really cares about that? We care about how it is presented and that does change.

                            Is any of this huge? I doub't it, but I don't know....I don't even "know" my understanding is entirely correct...
                            Steve
                            the Photographic Academy.com
                            SharpShooter Industries
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                            • #15
                              Originally posted by sk66 View Post
                              I say "apparent exposure" because "what" was recorded (the exposure) does not change, but who really cares about that? We care about how it is presented and that does change..
                              This is the one. It turns out whether white balance affects expsoure is all down to semantics.

                              What it does affect is the brightness of the final output. (RAW is not an output)

                              You can see the effect very clearly for your self. Take a RAW file that contains a scene the fills the cameras dynamic range (blown shadows and highlights) and in the RAW converter turn on the blinkies that highlight the blown pixels. Now move the WB slider to different settings and you will see the number of blown pixels change. Presumably this is because as you change the colour balance you are effectivly adjusting the brightness of the different RGB channels. This will cause different pixels to blow out.

                              So what does this mean in real life when shooting.

                              For me nothing: Since I shoot all shots in RAW and Auto WB I can be confident that my white balance is in the ball park. Therefore when I set the correct WB in post I'm only changing by small amounts, if this does cause some extra pixels to blow it is well within the latitude afforded by my 12 bit files.

                              If I shot JPEG then it may be more of an issue but there are so many other reasons I would need to pay more attention to WB before shooting that this pales into insignificance.

                              The only thing I can see this being important for is RAW conversion work flow. WB should be the first thing you change since it affects the brightness of the picture, if you made all of your other edits and then changed the WB it would affect everthing you had done before.
                              Fletch

                              << blog >> - flickr
                              Olympus E510 - Ok to edit and re-post on DPS only

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