9 Jun
2013
9 Jun
'13
6:26 p.m.
Hi Carsten,
Interesting. DVD-o-matic is using the same look-up tables for sRGB -> XYZ
conversion that OpenDCP uses. I will put some details in the manual.
As it happens I have recently been using the inverse of these transforms
for conversion in the opposite direction. We had been finding that the
resulting RGB images were too dark until I changed the transform slightly
(to a simpler gamma curve). This suggests that, perhaps, the current
transforms are wrong (and may be inclined to generate overly bright
images).
Perhaps we should try the modified transforms in DVD-o-matic and see how
that turns out. Your Blu-ray test might be handy here...
Best
Carl
On Sat, 8 Jun 2013, Carsten Kurz wrote:
Today I had to play a commercial BluRay, converted to
DCP with MakeMKV
and DVD-o-matic (0.89). It turned out much too bright on our Sony
SRX-R515. This is a fairly new installation and the calibration is
certainly perfect, I never see any issues on commercial DCPs and
trailers.
Initially I thought this was just a Gamma issue, but I found out that on
this machine the Gamma for DCI content is already maxed out at 2.6, I
can only set it lower.
It was a straight conversion, no intermediate conversion, no filters, I
chose REC709 in DVD-o-matic, and on the Sony projector our standard flat
DCI preset.
It wasn't subtle - about 30% of the movie showed decent contrast, most
other brighter scenes were very milky, and in darker scenes shadows were
torn into noisy dark green and blue. Detail was very good actually, I
chose a no-rescale conversion (flat no stretch).
This projector actually has a brightness, contrast and color saturation
slider. Usually I never touch these things, because on a properly
calibrated machine everything should be okay after the calibration. The
DCI flat preset had these sliders in their default positions, which were
100 for contrast, 50 for brightness, 50 for saturation.
I could actually fix the problem by reducing brightness to 30 and
reducing colour saturation to 45. I played the BluRay in parallel to the
HDMI input configured to REC709, switched back and forth and it matched
quite well. I did not have more time for perfection, there was still a
slight color shift between the two, but it was okay.
I guess I will have to send my BluRay calibration disc through the same
conversion to find out what is going on there.
Any ideas?
- Carsten
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