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Correct White Balance Doesn't Mean Correct Color??

 
 
Steve Wolfe
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      10-22-2005
> The term white balance means to balance the color temperature of light so
> that white object (a piece of white card) will reproduce as white.


(snip)

> Therefore physically, correct WB means correct color but not artistically.


Ideally, yes. But like I said, because of real-world deviations from the
ideal, just because you get *white* correct doesn't necessarily mean that
other colors will come out correctly. Take an LCD or a CRT, and set the
white balance correctly - white will be white. Then see if that magically
makes all of the colors come out correctly. Come back and tell us what you
find. Digital sensors aren't any different. It's not that your idea is
wrong, it's just that real-world devices simply don't live up to the
theoretical. If they did, you could take a picture, view it on any monitor,
and print it on any printer, and it would look the same in all cases.

steve


 
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Steve Wolfe
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      10-22-2005
> I don't think the monitor can cause the intrinsic image to be the
> wrong color if the white balance is correct. That is, if a known gray
> in the image *measures* gray (R=G=B) it doesn't matter what color it
> appears to the eye, the actual image is correct.


I have yet to see a monitor (CRT or LCD) where just setting the white
balance (without developing a full profile) will give you correct colors
across the spectrum, or even full neutrality from black to white. In fact,
just moving a calibration tool a few inches is enough to measure different
colors. In the ideal world that wouldn't be the case, but in the real
world, there are always tradeoffs between manufacturing costs and
tolerances.

steve


 
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Dave Martindale
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      10-23-2005
jim evans <(E-Mail Removed)> writes:
>I read in google groups where someone posted this statement in this
>group:


>". . white balance . . . is the first step but not quite the same
>thing [as correct color balance]. I.e., you can have poor color even
>if the white balance is set right. "


>Is this true? If so, why?


It's certainly true in general. Correct white balance means that
neutral colour (e.g. grey at various intensities, including white) looks
neutral. Correct colour means that *all* colours are reproduced
in a way that looks correct to the human eye.

Consider these examples:

A camera is set to B&W mode. All grey objects are accurately
reproduced, but all other colours are reproduced as grey too.

A camera has the colour saturation set too high. All grey objects
(which have no colour) will be reproduced accurately if the white
balance is correct, but all non-grey colours will be oversaturated and
thus not accurate.

More subtly: suppose that the RGB filters in the camera have spectral
response curves that do not match the human eye's colour matching
response, and that no linear combination of the camera filter responses
is equal to the human colour matching functions. This camera may be
easily adjusted for white balance, but its colour reproduction for many
colours will be somewhat wrong. Two things that look exactly the same
to the eye, but have different reflected-light spectra, may appear
different when photographed by this camera.

Basically, getting white balance correct is a tiny subset of the problem
of getting all colours correct.

Dave
 
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jim evans
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      12-24-2005
On Sun, 23 Oct 2005 06:41:36 +0000 (UTC), http://www.velocityreviews.com/forums/(E-Mail Removed) (Dave
Martindale) wrote:

>jim evans <(E-Mail Removed)> writes:
>>I read in google groups where someone posted this statement in this
>>group:

>
>>". . white balance . . . is the first step but not quite the same
>>thing [as correct color balance]. I.e., you can have poor color even
>>if the white balance is set right. "

>
>>Is this true? If so, why?

>
>It's certainly true in general. Correct white balance means that
>neutral colour (e.g. grey at various intensities, including white) looks
>neutral. Correct colour means that *all* colours are reproduced
>in a way that looks correct to the human eye.
>
>Consider these examples:
>
>A camera is set to B&W mode. All grey objects are accurately
>reproduced, but all other colours are reproduced as grey too.
>
>A camera has the colour saturation set too high. All grey objects
>(which have no colour) will be reproduced accurately if the white
>balance is correct, but all non-grey colours will be oversaturated and
>thus not accurate.
>
>More subtly: suppose that the RGB filters in the camera have spectral
>response curves that do not match the human eye's colour matching
>response, and that no linear combination of the camera filter responses
>is equal to the human colour matching functions. This camera may be
>easily adjusted for white balance, but its colour reproduction for many
>colours will be somewhat wrong. Two things that look exactly the same
>to the eye, but have different reflected-light spectra, may appear
>different when photographed by this camera.
>
>Basically, getting white balance correct is a tiny subset of the problem
>of getting all colours correct.


I assume then you don't think this method of getting colors correct
works http://www.rawworkflow.com/products/whibal ?

jim
 
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Dave Martindale
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      12-24-2005
jim evans <(E-Mail Removed)> writes:

>>Basically, getting white balance correct is a tiny subset of the problem
>>of getting all colours correct.


>I assume then you don't think this method of getting colors correct
>works http://www.rawworkflow.com/products/whibal ?


That's a product that helps you set white balance. With incorrect white
balance, every colour will be wrong, even greys. So getting white
balance correct is important - but it doesn't mean that all colours will
be correct.

Dave
 
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Ole Larsen
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      12-24-2005
Dave Martindale skrev:
> jim evans <(E-Mail Removed)> writes:
>
>
>>>Basically, getting white balance correct is a tiny subset of the problem
>>>of getting all colours correct.

>
>
>>I assume then you don't think this method of getting colors correct
>>works http://www.rawworkflow.com/products/whibal ?

>
>
> That's a product that helps you set white balance. With incorrect white
> balance, every colour will be wrong, even greys. So getting white
> balance correct is important - but it doesn't mean that all colours will
> be correct.
>
> Dave


I think color balance is a interesting subject. Example:
Youīre shooting under mixed artificial lightning. Your eyes have
adapted to that in secs. so it all looks natural.
How do you afterwards make the pictures?
Tecnically correct (meaning looking "wrong", weird)
or
As you remember (meaning wrong = as your adapted eyes "saw" it)

Another example: On a hot hazy day - do you filter the large
amount of UV so it looks "natural"=as your adapted eyes saw it?

And then again - if you shoot raw, you have all the information needed
to adjust to whatever you prefer.

A while ago I photographed 68 paintings for a artist I know. They were,
one aften another, placed on a "white" cardboard. Lightning was 2
halogen 500 w. Custom WB was set on the cardboard. As they were of diff.
luminousity, the exposure varied and thus the WB. What to do?
In the raw-converter adjust the WB on the cardboard-"frame" of the 1.
picture and use that WB on the whole batch - and it worked fine.



--
Med venlig hilsen, Ole Larsen.
New Images And Design 2005-11-17
http://home.tiscali.dk/muggler
 
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jim evans
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      12-24-2005
On Sat, 24 Dec 2005 05:51:04 +0000 (UTC), (E-Mail Removed) (Dave
Martindale) wrote:

>jim evans <(E-Mail Removed)> writes:
>
>>>Basically, getting white balance correct is a tiny subset of the problem
>>>of getting all colours correct.

>
>>I assume then you don't think this method of getting colors correct
>>works http://www.rawworkflow.com/products/whibal ?

>
>That's a product that helps you set white balance. With incorrect white
>balance, every colour will be wrong, even greys. So getting white
>balance correct is important - but it doesn't mean that all colours will
>be correct.


Thanks very much for your replies.

jim
 
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jim evans
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      12-24-2005
On Sat, 24 Dec 2005 05:51:04 +0000 (UTC), (E-Mail Removed) (Dave
Martindale) wrote:
> getting white balance correct is important - but it doesn't mean
>that all colours will be correct.\


Another question. If you're shooting RAW and get white balance
correct, during the conversion isn't the RAW converter (in my case
ACR) supposed to adjust the remaining colors to make them correct?

jim
 
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Dave Martindale
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      12-27-2005
jim evans <(E-Mail Removed)> writes:
>On Sat, 24 Dec 2005 05:51:04 +0000 (UTC), (E-Mail Removed) (Dave
>Martindale) wrote:
>> getting white balance correct is important - but it doesn't mean
>>that all colours will be correct.\


>Another question. If you're shooting RAW and get white balance
>correct, during the conversion isn't the RAW converter (in my case
>ACR) supposed to adjust the remaining colors to make them correct?


What white balance actually does is adjust the intensity of the red,
green, and blue channels with respect to each other. Done properly,
greys should be grey through their whole intensity range, and other
colours will also be adjusted towards the correct colour.

However, there's only so much that the white balance adjustment can do.
You can expect pretty accurate colour with continuous-spectrum lights
like incandescents, carbon arc, or sunlight. The illuminating light
from all of these contains all wavelengths of light, and the colour
temperature just reflects the fact that hotter sources (e.g. sun, carbon
arc) are relatively richer in blue than cooler ones (incandescents).

But some lamps (fluorescents (particularly cheap ones), sodium or
mercury vapour streetlights, etc) put out light which has a very spiky
spectrum. Your eye doesn't see colours accurately under these lights,
and cameras don't either. The problem isn't simply red/green/blue
ratio, and adjusting white balance won't give accurate colours.

(It would be nice if your camera could at least see the same wrong
colours as your eye, but that's difficult too).

Dave
 
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