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Re: Masking on Rank Ursa



        Reply to:   RE>Masking on Rank Ursa

Reply to Serge at Supersuite Post:
We usually don't use the Rank provided masks because we have modified the
Dichroics in the Cell Box to improve the light throughput and thus the signal
to noise of the machines.  This changes the colorimetry analysis of the URSA
somewhat and makes the Rank provided masks inaccurate especially for Blue. 
But we do believe in correcting colorimetry errors with an accurate mask
tailored to the film stock being scanned.  This has forced us to custom tweek
and use the User 1 and 2 masks constantly.  (I wish FUJI made a TAF equivalent
so mask values could be set up for their stock).  If you take a look at the
"Masking tips" page on the telecine group engineering page it might help you
set custom masking values.  The strange Gamma interaction of the URSA Color
Channel is caused by the Gamma function being performed before Masking instead
of after as it should be.  Its a shame Rank chose to design the Color Channel
in this way as it makes it almost impossible to grade Gamma if you use Masking
unless you use a downstream processing channel such as the DaVinci 8:8:8,
POGLE DCP, or the Copernicus 4:4:4.  The MK3 machines did Gamma adjustment
after Log Masking and did not have this problem, at least for Gamma.  Maybe
someone from Rank Cintel could inform the group why it was designed this way. 
If you have Arcus you only have the URSA color channel so it is a big problem.
 Has anyone figured out how to modify the URSA color channel to do Gamma after
Masking?
Dave Corbitt

===========================================
On Oct 18, 1995 Serge Robert wrote:

>The Rank Ursa operation manual suggests we use the no 2 mask when transfering
>Kodak EXR negative.
>Although we have found that excellent results can be achieved without it, the
>mask does render primary colors in such a way as to give the image a more
>"print-like" feel.
>However, I have noticed a strange reaction to this mask by our gamma
trackerball
>controls (we are using the Arcas controller as we have neither a daVinci nor
a
>Poggle attached to the Rank). For instance, moving the gammas towards red
>actually adds cyan to the image.
>Are you experiencing something similar?
>Are you infact using these maskings at all?

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