RAW vs White balance

Started Nov 20, 2006 | Discussions thread
ptodd Senior Member • Posts: 1,327
Re: interesting criticisms

GordonBGood wrote:

ptodd wrote:

Perhaps if you have time you could download the software and do
your own tests, with all appropriate controls in place?

I might even do this myself sometime, but not right now...

Are you the original author?

No, I'm not, I just posted the link their as I thought that might make it easier to find.

I don't need the software, as I have my own on which I base my raw
conversions that can be set to do the same thing.

There isn't a lot of point of repeating the experiments, as I don't
have and won't be getting a DS and other cameras may behave

Ah, I didn't realise that. What camera do you have? I think interesting results can be obtained from any *ist, or any camera that shoots raw. It would be good to know if they do behave differently.

I may have access to a K100D and/or eventually a K10D, and will be
checking that ISO settings are accurate but won't be much concerned
with the second range of tests other than that for my stated

It seems to me there is still something to be gained (and little to be lost) by using ISO 800; wether or not the gain is significant is another matter, and you may be right in practice that all of the lower gradations are in the noise anyway. Still, I would say it's better to have a more accurate reading of even the noisiest part of the signal and it seems there is little to gain from high ISOs.

If I saw such a difference in ISO sensitivity that is not
a factor of two as between the ISO 200 and ISO 400 shots, I would
be looking for the reasons for this and aperture would be a very
important parameter (I would have used full manual mode for these
tests and stated aperture values).

Indeed, I pretty much assumed that they wouldn't bother to do a test in any other mode, but you're right there is no explicit indication of this.

As to the first range of tests showing a turned down sensitivity
for very "warm" high red Tungsten WB shots, I wouldn't be surprised
that this could be true for the reason of giving more Red channel
headroom and that there is a private tag in the PEF file telling
the raw convertor to adjust exposure for this after WB
compensation. Again, full exposure values including aperture are
an important part of confirming this.

I've never written any raw software, but I'd be surprised if the program used here would take any notice of such a tag. I haven't looked at the source, even, but I'd expect it to just skip straight past the header and run through the image data in a very crude, direct, way with no interpretation of any tags telling it to do differently. Can you confirm or deny this, or offer any other light on the subject from your own experience of raw software?

Neither of these tests, other than the illogical results of the ISO
sensitivity justify casting doubt on the useabiliy of PEF raw image
files, especially when they are not backed up with full test

The bottom line as far as I'm concerned is that we have graphs showing a proportionally different distribution of intensities among the colour channels in different images of the same scene, where there should be none. Details of exposure should be controlled, but I don't see how that would change the basic fact.

I'm going to try this out myself, later. Probably. If I get 'round to it.


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