[argyllcms] Re: White Point

  • From: Hening Bettermann <hein@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 7 Nov 2015 23:27:32 +0100

On 07 Nov 2015, at 21:27h, Iliah Borg <iliah.i.borg@xxxxxxxxx> wrote:


In floating point, the Teflon tape reads 1.000-1.000-1.000. (As does the
whitest patch of the left/upper part of the ColorCheckerPassport; but
RawDigger shows higher values for the Teflon than for the Passport patch).

You probably have clipping in the raw conversion, since different raw values
are mapped to the same value in the raw converter.

First, it would be good to see the raw file in question (if anything, to get
an idea of the exposure and flare. It may help if there is a shot of the
whole setup, even taken with a phone, to see the locations of the camera, the
lights, the target. Second, if a raw converter clips the highlights, the
right thing to do is to decrease the exposure. If it is a substantial
clipping, you may want to present the case to the developer of the raw
converter. Third, what is that you are using for white balance? Second grey
from CCP?

Best regards,
Iliah Borg
LibRaw, LLC

Hi Iliah,

thank you for your very fast response.
For white balance, I used the Teflon tape, since I read that it is almost 100%
The raw is here for FTP download:
file name: _DSC2375.ARW
server: landshape.net
login name: ad_hoc@xxxxxxxxxxxxx
password: come_in
and an iPhone shot of a quick reconstruction of the setup at the same place,

I can not show the camera, because it's in for repair (that's why I find time
for the darkroom ;-) )

By 'decrease the exposure', you mean in the raw converter, or choosing a lower
exposed frame?
Lowering the exposure in Iridient requires 0.62 EVs to make the last red pixel
disappear (at 100%). I might as well choose a frame exposed 1/3 EV lower and
then do the rest in Iridient?

And there is another thing I don't understand how interferes with all this.
Iridient has for the a7r a default black level of 78 and white level of 246.
How do these come in?

Best regards -
Hening Bettermann, www.landshape.net

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