Does white balance affect exposure.

[OsmosisStudios]

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.

[dcclark]

Originally Posted by OsmosisStudios

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.

[Doug Pardee]

Originally Posted by Sixpak

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."

[sk66]

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...

[fletch]

Originally Posted by sk66

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.

[Sime]

Originally Posted by fletch

I've reported the spam - Don't click the links!!!!

we're a spam fighting machine!.... *high five*

[sk66]

Originally Posted by fletch

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.

Hmm, I wonder if maybe that's why WB is the first adjustment in Lightroom's Develop module? (and sharpening is the last..a pretty well known "rule" for processing sequence)

Them Adobe people are pretty smart.....

[fletch]

Originally Posted by Sime™

we're a spam fighting machine!.... *high five*

*high fives*

I even cleaned up the mess!

[vandergus]

I think Doug Pardee's original explanation says it best. Also this bit by fletch...

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.

I think we've established that adjusting the WB in post can slightly change the brightness of the final image.

Now a follow-up question. Since some camera meters take color data into account and not just luminance data (like Nikon's 3D color matrix metering), will the camera change the exposure based on the selected white balance. For example, say you have "daylight" white balance set and the camera chooses an exposure of f/8, 1/800, ISO 200. Now you change the white balance to "cloudy". Will the camera shift the exposure a little, say f/8, 1/600, ISO 200 to account for the different color balance or will it keep the same exposure. Just curious.

[dcclark]

Originally Posted by vandergus

I think we've established that adjusting the WB in post can slightly change the brightness of the final image.

This is correct (although adjusting the WB in-camera does not change the metered values).

Originally Posted by vandergus

Now a follow-up question. Since some camera meters take color data into account and not just luminance data (like Nikon's 3D color matrix metering), will the camera change the exposure based on the selected white balance. For example, say you have "daylight" white balance set and the camera chooses an exposure of f/8, 1/800, ISO 200. Now you change the white balance to "cloudy". Will the camera shift the exposure a little, say f/8, 1/600, ISO 200 to account for the different color balance or will it keep the same exposure. Just curious.

No, I don't think so. I'm not 100% clear on how the color part of Color Matrix Metering works, except that I believe it is used to help figure out contrasting edges (and thus perhaps figure out what your subject is).

Of course, there's an easy solution to this: go set up your camera, on a tripod, in controlled lighting situations. Meter using several different color balances. See what happens in the EXIF. I would bet money that there will be no difference, if you truly do control for lighting.