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SD10: a raw file fact about White Balance

 
 
David Kilpatrick
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      05-23-2004
This is not a plug for the SD10, or a knock either. Using many different
cameras, I've found that on the whole 'white balance' is rarely a
physical alteration to the raw file (it is always a physical alteration
to TIFF or JPEGs produced in camera). With .NEF, .MRW, .ORF and probably
also with Canon files, white balance is just a 'tag' added to the raw
file. The camera always records using the full sensitivity of the sensor
across the spectrum, the WB setting may alter overall exposure to permit
the necessary channel adjustments, but it doesn't change the raw file.

When you come to import the picture, if you have made an error and set
tungsten in daylight or vice-versa, you can simply change the white
balance in the raw file converter. I have not noticed any loss in
quality when doing this.

With the Sigma SD10, the situation is quite different. If you set
Tungsten, you might as well be loading tungsten film. The actual raw
file is altered in camera to have a correct channel balance for tungsten
light. I've just shot a set of pix in daylight using tungsten balance,
in error, and found that no amount of adjustment can correct them. On
the other hand, I've found that auto or custom set white balances on the
SD10 are very accurate. There is adjustment of course, with quite a wide
range, but you can't just change a wrongly balanced file back to normal
as you can with most raw conversions.

What I do not know is whether the camera uses differential gain in the
three layers when you change white balance, or whether it has a
processing stage in between the usual A-to-D and the .XF3 file creation.

It's another example of how different the concept is, and how
differently it works. I don't necessarily like it. It can be useful to
change the white balance when importing the image, but the SD10 really
doesn't allow that.

David

 
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Helge Olsen
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      05-23-2004

"David Kilpatrick" <(E-Mail Removed)> wrote in message
news:c8r60p$rf6$(E-Mail Removed)...
> This is not a plug for the SD10, or a knock either. Using many different
> cameras, I've found that on the whole 'white balance' is rarely a
> physical alteration to the raw file (it is always a physical alteration
> to TIFF or JPEGs produced in camera). With .NEF, .MRW, .ORF and probably
> also with Canon files, white balance is just a 'tag' added to the raw
> file. The camera always records using the full sensitivity of the sensor
> across the spectrum, the WB setting may alter overall exposure to permit
> the necessary channel adjustments, but it doesn't change the raw file.
>
> When you come to import the picture, if you have made an error and set
> tungsten in daylight or vice-versa, you can simply change the white
> balance in the raw file converter. I have not noticed any loss in
> quality when doing this.
>
> With the Sigma SD10, the situation is quite different. If you set
> Tungsten, you might as well be loading tungsten film. The actual raw
> file is altered in camera to have a correct channel balance for tungsten
> light. I've just shot a set of pix in daylight using tungsten balance,
> in error, and found that no amount of adjustment can correct them. On
> the other hand, I've found that auto or custom set white balances on the
> SD10 are very accurate. There is adjustment of course, with quite a wide
> range, but you can't just change a wrongly balanced file back to normal
> as you can with most raw conversions.
>
> What I do not know is whether the camera uses differential gain in the
> three layers when you change white balance, or whether it has a
> processing stage in between the usual A-to-D and the .XF3 file creation.
>
> It's another example of how different the concept is, and how
> differently it works. I don't necessarily like it. It can be useful to
> change the white balance when importing the image, but the SD10 really
> doesn't allow that.
>
> David
>


This leads me to think that the SD10's "raw" files aren't indeed raw. The
whole point of raw is to NOT alter the result in any way from what's
recorded by the sensor. The sensor should not give any thought of white
balance in order to record an image. IE. the Sigma cameras do not record
true RAW files. They just waste space by not compressing altered images. So
much for "professional"...

/Helge


 
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Mark M
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      05-23-2004


> It's another example of how different the concept is, and how
> differently it works. I don't necessarily like it. It can be useful to
> change the white balance when importing the image, but the SD10 really
> doesn't allow that.
>
> David


If what you are saying is accurate, then the Sigma...
....does NOT have a truly RAW mode at all.

If true, this is a horrendous oversight (or intentional, but poor design).


 
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E. Magnuson
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      05-23-2004
On 2004-05-23, Helge Olsen <(E-Mail Removed)> wrote:
> This leads me to think that the SD10's "raw" files aren't indeed raw.


One, I think that David may be mistaken. This is an area where
Laurence M can speak with authority if we've not chased him away.

> whole point of raw is to NOT alter the result in any way from what's
> recorded by the sensor.


Be careful here. The line is not clear cut. What about ISO
sensitivity? The "sensor" seems the same number of photons for the
same EV; the ISO is usually just changes to the analog amplifier gain.
There may be other signal conditioning (like noise reduction) that is
similarly performed on the analog signal before conversion. There may
be some digital processing done. AFAIK, no camera maker makes any
disclosure about exactly how raw is raw. Perhaps we should call it
"rare" or "al-dente" instead.


--
Erik


 
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Alfred Molon
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      05-23-2004
David Kilpatrick <(E-Mail Removed)> wrote:

>What I do not know is whether the camera uses differential gain in the
>three layers when you change white balance, or whether it has a
>processing stage in between the usual A-to-D and the .XF3 file creation.


Can the XF3 files be imported directly into the RAW converter of
Photoshop or are they only compatible with the Sigma converter ?
--

Alfred Molon
------------------------------
http://groups.yahoo.com/group/Olympus_405080/
Olympus 5050 resource - http://www.molon.de/5050.html
Olympus 5060 resource - http://www.molon.de/5060.html
Olympus 8080 resource - http://www.molon.de/8080.html
 
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Roland Karlsson
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      05-23-2004
"E. Magnuson" <(E-Mail Removed)> wrote in news:QU9sc.8569$ZZ1.378809
@twister.tampabay.rr.com:

> Be careful here. The line is not clear cut. What about ISO
> sensitivity? The "sensor" seems the same number of photons for the
> same EV; the ISO is usually just changes to the analog amplifier gain.
> There may be other signal conditioning (like noise reduction) that is
> similarly performed on the analog signal before conversion. There may
> be some digital processing done. AFAIK, no camera maker makes any
> disclosure about exactly how raw is raw.


Agree. The main purpose of any format is to be a good
carrier for the photo. No format is entirely RAW. All
formats are digital - the RAW info is analog. All RAW files
- except Foveon, I think - are processed for noise reduction.
And - as you say - ISO sensitivity might be done by different
amplification.


/Roland
 
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Peter A. Stavrakoglou
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      05-23-2004
"Alfred Molon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
> David Kilpatrick <(E-Mail Removed)> wrote:
>
> >What I do not know is whether the camera uses differential gain in

the
> >three layers when you change white balance, or whether it has a
> >processing stage in between the usual A-to-D and the .XF3 file

creation.
>
> Can the XF3 files be imported directly into the RAW converter of
> Photoshop or are they only compatible with the Sigma converter ?


XF3 files can be imported directly into PhotoShop CS.


 
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E. Magnuson
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      05-24-2004
On 2004-05-23, Roland Karlsson <(E-Mail Removed)> wrote:
> "E. Magnuson" <(E-Mail Removed)> wrote in news:QU9sc.8569$ZZ1.378809
> @twister.tampabay.rr.com:
>
> All RAW files - except Foveon, I think - are processed for noise reduction.


I'd bet Foveon data is processed for noise reduction as well.
I can't prove it, but that's my reading of some of the hints
dropped in talks and papers. It would also make sense because
of the analog background of some of their people.

--
Erik

 
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Bart van der Wolf
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      05-24-2004

"David Kilpatrick" <(E-Mail Removed)> wrote in message
news:c8r60p$rf6$(E-Mail Removed)...
SNIP
> When you come to import the picture, if you have made an
> error and set tungsten in daylight or vice-versa, you can simply
> change the white balance in the raw file converter. I have not
> noticed any loss in quality when doing this.


That's a correct evaluation of what a Raw file comprises. It may have some
on chip noise reduction applied (e.g. dark field reduction), but the file
data is essentially Raw, ADC quantized data (e.g. still in Bayer CFA
"color", or "as captured"). Other camera settings are only tags, used as
defaults in the Raw converter firm/software or in-camera JPEG creation.

SNIP
> What I do not know is whether the camera uses differential gain
> in the three layers when you change white balance, or whether it
> has a processing stage in between the usual A-to-D and the .XF3
> file creation.


There will probably be little difference in the hit on S/N ratio, perhaps
differential gain being marginally more accurate (avoiding cumulative
integer rounding errors unless, less likely, rational number arithmetic is
used throughout). Subsequent color balance conversions are in any case to be
avoided if accuracy is a concern.

> It's another example of how different the concept is, and how
> differently it works. I don't necessarily like it. It can be useful to
> change the white balance when importing the image, but the SD10
> really doesn't allow that.


Interesting observation, thanks for sharing.

Bart

 
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Bart van der Wolf
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      05-24-2004

"Alfred Molon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
SNIP
> Can the XF3 files be imported directly into the RAW converter of
> Photoshop or are they only compatible with the Sigma converter ?


XF3 seems to be compatible with the latest (v2.2) Adobe Raw Converter (or
rather ARC is compatible with XF3s).

Bart

 
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