Curious RAW quirk?

On Mon, 12 Oct 2009 08:37:22 -0700, John McWilliams
wrote:

celcius wrote:
Hi all!

I took in-house photos at a party, setting the WB to flash and using an
external Canon flash on my Eos 5D MarkII.
What puzzles me is when I work on the Raw photo in Photoshop CS3 and
the white balance shows as "as shot", if I change it to "Flash" (which
was the WB setting on my camera) , I get a cooler temp. Why please this
difference?

The RAW processor has a different idea of what "Flash" means than does
the camera!
How much a difference?
I generally find that if I leave the WB on auto, it does a superb job on
85% of my shots. The "auto" function in the processor, though, sometimes
comes up better than the camera's; sometimes not as good.

I find this as well no matter how I try to calibrate the WB for a
given shot. If I just trust in my knowledge instead of trying to
overthink the process I get much better results.

But alas, I am arrogant in this respect.

On Fri, 16 Oct 2009 17:42:56 +1000, Bob Larter
wrote:

SkinnerOne wrote:
On Mon, 12 Oct 2009 08:37:22 -0700, John McWilliams
wrote:

celcius wrote:
Hi all!

I took in-house photos at a party, setting the WB to flash and using an
external Canon flash on my Eos 5D MarkII.
What puzzles me is when I work on the Raw photo in Photoshop CS3 and
the white balance shows as "as shot", if I change it to "Flash" (which
was the WB setting on my camera) , I get a cooler temp. Why please this
difference?
The RAW processor has a different idea of what "Flash" means than does
the camera!
How much a difference?
I generally find that if I leave the WB on auto, it does a superb job on
85% of my shots. The "auto" function in the processor, though, sometimes
comes up better than the camera's; sometimes not as good.

I find this as well no matter how I try to calibrate the WB for a
given shot. If I just trust in my knowledge instead of trying to
overthink the process I get much better results.

But alas, I am arrogant in this respect.

With my Canon DSLRs, I find that AutoWB works pretty well 99% of the time.

Yep. And it's that other 1% of the time that I "THINK" I am right that
proves me wrong!

On Mon, 12 Oct 2009 14:56:34 -0800, (Floyd L. Davidson)
wrote:
: "celcius" wrote:
: I think you've got a point in saying that setting the WB on the camera has
: very little incidence in Raw mode. John says that leaving it on "auto" is
: fine.
:
: WB has no effect on the camera raw data. It is a
: correction applied only when that data is converted to a
: JPEG. The camera always generates a JPEG for viewing,
: which is also used to generate an histogram. But if you
: don't "shoot JPEG", it is not saved as a file.
:
: I thought, reading the posts here in the past, that it was always better to
: set the proper WB even when shooting in Raw mode. Now, I'm back to square 1
: ;-)
:
: Setting WB depends on what you want. It can be, for
: example, set to provide no correction in order to get an
: accurate histogram. It can be set to "auto", just to
: provide Exif data for what the camera calculates as the
: correct adjustment. ...

Except that the Exif data don't tell you that. The field just says "Auto". It
would be nice if the camera told you its determination of the color
temperature of the ambient light, but my Canons don't.

Bob

Robert Coe wrote:
On Mon, 12 Oct 2009 14:56:34 -0800, (Floyd L. Davidson)
wrote:
: "celcius" wrote:
: I think you've got a point in saying that setting the WB on the camera has
: very little incidence in Raw mode. John says that leaving it on "auto" is
: fine.
:
: WB has no effect on the camera raw data. It is a
: correction applied only when that data is converted to a
: JPEG. The camera always generates a JPEG for viewing,
: which is also used to generate an histogram. But if you
: don't "shoot JPEG", it is not saved as a file.
:
: I thought, reading the posts here in the past, that it was always better to
: set the proper WB even when shooting in Raw mode. Now, I'm back to square 1
: ;-)
:
: Setting WB depends on what you want. It can be, for
: example, set to provide no correction in order to get an
: accurate histogram. It can be set to "auto", just to
: provide Exif data for what the camera calculates as the
: correct adjustment. ...

Except that the Exif data don't tell you that. The field just says "Auto". It
would be nice if the camera told you its determination of the color
temperature of the ambient light, but my Canons don't.

You looked at this:

White Balance : Auto

That tells what the camera was set to. But the data
looks like this (for a Nikon NEF file):

Color Balance 1 : 1.460938 1.878906 1 1

Those are channel multipliers.

Canon CRW and CR2 files have different ways of embedding
the data. Use /exiftool/ on a Canon file (in particular
take a look at the JPEG file produced in the camera),
and you'll find all kinds White Balance data. This is
from an example 300D CRW file that I found on the net.
Note that it lists a series of presets as well as the
camera generated auto settings.

Color Temperature : 5200
WB RGGB Levels Auto : 2092 830 833 962
WB RGGB Levels Daylight : 1957 830 833 1028
WB RGGB Levels Shade : 2301 830 833 875
WB RGGB Levels Cloudy : 2123 830 833 939
WB RGGB Levels Tungsten : 1417 919 922 1739
WB RGGB Levels Fluorescent : 1709 843 846 1418
WB RGGB Levels Flash : 2189 830 833 931
WB RGGB Levels Custom : 1957 830 833 1028
WB RGGB Levels Kelvin : 1953 830 833 1025
...
WB RGGB Levels : 2092 830 833 962
Blue Balance : 1.156945
Red Balance : 2.515935

The last three lines show the actual data. The first
one is raw data and the second and third lines are
normalized Blue and Red multipliers for the average of
the two Green channels set to 1.

If that is translated to the same data format that Nikon
uses, it looks like this:

Color Balance : 1.156945 2.515935 1 1

Of course, I haven't looked at a raw file from your
particular camera either... If you can post one
somewhere on the net that I can download, I'd be
interested in looking at it.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

"Robert Coe" wrote:
On Mon, 12 Oct 2009 14:56:34 -0800, (Floyd L. Davidson)
wrote:
: "celcius" wrote:
: I think you've got a point in saying that setting the WB on the camera
has
: very little incidence in Raw mode. John says that leaving it on "auto"
is
: fine.

If you have information on what the WB was (e.g. daylight, cloudy, tungsten)
and it's applicable to the scene, it's sometimes worth setting, since you
may forget what the light was like. Also, there needs to be a "neutral"
setting that doesn't change colors. For example, when the subject is a light
source (e.g. a sunset sky), white balance doesn't make sense. But that's
another rant.

: WB has no effect on the camera raw data. It is a
: correction applied only when that data is converted to a
: JPEG. The camera always generates a JPEG for viewing,
: which is also used to generate an histogram. But if you
: don't "shoot JPEG", it is not saved as a file.
:
: I thought, reading the posts here in the past, that it was always
better to
: set the proper WB even when shooting in Raw mode. Now, I'm back to
square 1
: ;-)

That's my opinion. Most raw converters will let you change the WB, but
setting it can function as a memo of what the light was like. Especially if
you do a custom WB measurement.

: Setting WB depends on what you want. It can be, for
: example, set to provide no correction in order to get an
: accurate histogram. It can be set to "auto", just to
: provide Exif data for what the camera calculates as the
: correct adjustment. ...

Except that the Exif data don't tell you that. The field just says "Auto".
It
would be nice if the camera told you its determination of the color
temperature of the ambient light, but my Canons don't.

But DPP might. I think Lightroom will calculate an AWB for you and you can
see what it is (and adjust starting from there).

Remember, though, that AWB cannot, in principle, tell the difference between
a white shirt in pink light and a pink shirt in white light. A
non-color-blind human looking at a scene has (or can figure out) a lot of
information about what things should look like and does feed that back into
his/her color perception of the scene. Cameras can't do that. We can get
fooled, but camreas get fooled a lot more easily.

--
David J. Littleboy
Tokyo, Japan



Bob

On Sun, 18 Oct 2009 02:50:04 +0900, "David J. Littleboy"
wrote:
:
: "Robert Coe" wrote:
: On Mon, 12 Oct 2009 14:56:34 -0800, (Floyd L. Davidson)
: wrote:
: : "celcius" wrote:
: : I think you've got a point in saying that setting the WB on the camera
: has
: : very little incidence in Raw mode. John says that leaving it on "auto"
: is
: : fine.
:
: If you have information on what the WB was (e.g. daylight, cloudy, tungsten)
: and it's applicable to the scene, it's sometimes worth setting, since you
: may forget what the light was like. Also, there needs to be a "neutral"
: setting that doesn't change colors. For example, when the subject is a light
: source (e.g. a sunset sky), white balance doesn't make sense. But that's
: another rant.
:
: : WB has no effect on the camera raw data. It is a
: : correction applied only when that data is converted to a
: : JPEG. The camera always generates a JPEG for viewing,
: : which is also used to generate an histogram. But if you
: : don't "shoot JPEG", it is not saved as a file.
: :
: : I thought, reading the posts here in the past, that it was always
: better to
: : set the proper WB even when shooting in Raw mode. Now, I'm back to
: square 1
: : ;-)
:
: That's my opinion. Most raw converters will let you change the WB, but
: setting it can function as a memo of what the light was like. Especially if
: you do a custom WB measurement.
:
: : Setting WB depends on what you want. It can be, for
: : example, set to provide no correction in order to get an
: : accurate histogram. It can be set to "auto", just to
: : provide Exif data for what the camera calculates as the
: : correct adjustment. ...
:
: Except that the Exif data don't tell you that. The field just says "Auto".
: It
: would be nice if the camera told you its determination of the color
: temperature of the ambient light, but my Canons don't.
:
: But DPP might. I think Lightroom will calculate an AWB for you and you can
: see what it is (and adjust starting from there).

DPP doesn't. If I'm not happy with the "Auto" WB, and therefore choose the
"Color Temperature" setting, I'd like it to start with the color temperature
that it used to produce the auto result. But it doesn't; it always starts at
5200 degrees K, Canon's idea of daylight. As Floyd Davidson pointed out
earlier today, the actual color temperature assumption must be encoded in the
RAW data, and therefore known to DPP, but just try to find it.

Bob