[opendtv] Re: RGB mania
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 16 Jan 2005 09:35:43 -0500
At 8:46 AM -0600 1/15/05, Doug McDonald wrote:
> >We want the "printing" latitude we enjoy today with film
>>>negative, where we have enough information to bring out details in
>>>the blacks
>REALLY?
>
>I have never ever seen a movie with detail in the blacks.
How sad...
There are many classics that take full advantage f the ability to
push blacks when there are details there that the cinematographer and
director want you to see. Horror and murder flicks are a good
example; the director MAY want you to see the perp creeping through
the shadows to get the full dramatic impact. Then again, they may
want you to be completely surprised, in which case they will tend to
suppress the details in the blacks.
What is important to this discussion is that they have the ability to
do this in post.
Likewise, you need lot's of headroom in the whites and specular
highlights in order to deal with scenes with very high contrast. One
of the biggest weaknesses of HDTV cameras is that they cannot handle
scenes with extreme contrast. I have seen some excellent demos of
this at conferences. The classic problem is shooting outdoors with
talent/objects moving from shadows to full sunlight. I saw one
example shot on a street in Hollywood, that has trees planted
periodically along the sidewalks. The camera was being trucked along
the sidewalk. moving from full sunlight to shade. In the shade you
could see the details in the sidewalk, but in full sunlight, it was
just "bloomin" white. You can imagine what happened to the talent
walking in and out of the shade.
With film, this kind of scene is not a major challenge. There is
plenty of headroom to handle the specular highlights in the bright
areas. In post you can make this scene look perfectly natural. With
an electronic HD camera you are SOL, even with someone trying to
shade the camera on the fly.
Another example came from the DOP for Sony Picture's Joan of Arcadia,
during the Sony press conference at NAB last year. The series is shot
using the CineAlta camera. They has a series of shots at an outdoor
location, and they could not get the look they wanted because of the
high contrast outdoor conditions (more on this in a moment). So they
flew a huge gauze screen over the set to cut down on the ambient
light. Not only did this help with the high contrast scenes, but the
shoot ran a bit late and they were able to bounce lights off of the
screen to provide fill light as the ambient light faded.
All of that being said, there is another consideration here. if Doug,
or anyone for that matter, goes to the theater, they are likely to
see something that is different than what they would see on a GOOD
home theater system. The theater projection combined with the
characteristics of the release print provide considerably more
dynamic range than most HDTV displays, although the differences are
narrowing with some of the new display technologies. Even more
important, the ambient light levels in the theater are very low,
allowing for the maximum dynamic range, with the ability to perceive
details at both ends of the luma range.
For home theater, you are starting from a severe deficit. First, the
film has been transferred to an electronic medium that does not
provide the dynamic range needed in the blacks and whites: the
colorist can emphasize the most important areas of the image, but
this involves compromising the rest fo the image. Second, most
people adjust their displays for typical room lighting conditions,
not for a darkened room. Thankfully, most of the new HD capable
displays are providing multiple memories and presets for the display
setting; but you still need to tweak each memory or preset to
properly calibrate the display for both the ambient light conditions
and the characteristics of the source material.
Everyone should have a copy of Joe Kane's Video Essentials, so that
they can learn how to properly calibrate their displays to maximize
the perception of the full dynamic range. I have seen many displays
that are set up in this manner. With the room darkened they look
fantastic, however, as the ambient light level is increase they tend
to look rather flat, with little contrast. This is why most consumers
push the brightness and contrast, theyeby sacrificing much of the
available dynamic range that the displays is capable of delivering.
>Do you in fact, if you use a gray card or incident light
>meter for setting film exposure, correctly rate the film speed
>to get details in the blacks? That is, set the ASA rating
>an absolute minimum of 2/3 stop slower than the manufacturers
>ratings and more typically 1 or 1 1/3 stop slower? IF using
>a spot meter, do you set the exposure so that the absolute
>darkest part of the scene is well up on the toe?
That is the decision of the DOP/Cinematographer, based on the look
that the director is trying to achieve. I cannot imagine why you
would set the blackest black well up on the toe - this would waste
much of the dynamic range that the negative is capable of capturing.
I was just looking at a paper on the Kodak Cineon scanner (10 bit).
Here is where they set both the blacks and average whites:
http://www.dotcsw.com/doc/cineon1.pdf
For a normally-exposed Cineon Digital Negative, a 90% white card will
be recorded at a code value of 685. The Dmin of the film is set to
95, representing the blackest black that can be recorded (approx. a
1% black card). In converting from 10-bits to 8-bits, the range of
code values from 95 to 685 are mapped to an output range of 0 to 255.
In between these end points, it is necessary to implement the gamma
correction that is described herein.
Thus the blackest black is set where the toe begins to rise, while
the nominal whites are WELL below the top of the code range. The
paper goes on to talk about how to capture some of the specular
highlights when converting to the 8 bit range used for video
distribution today.
The biggest reason that we do not see much detail in the blacks or
whites for video today is the limited 8 bit dynamic range. More
justification for moving to 10 bits for emission encoding.
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