[Lumiera] a single digit??

Hendrik Boom hendrik at topoi.pooq.com
Fri Feb 8 03:07:03 CET 2013

On Thu, Feb 07, 2013 at 08:53:09PM +0100, Ichthyostega wrote:
> Hello Hendrik,
> just saw you placed a question/annotation some time ago:
>  Quality::
>         High-quality, cinema grade digital video material
>         requires crisp-quality results with no concessions made throughout the
>         entire workflow that might compromise quality of the final work.
>         A common requirement is the ability to reproduce all rendering
>         calculations down to a single digit.
> > ??What does this mean, a single digit??
> What it means, technically, is that rendering should be deterministic and that
> we should care for rounding and number representation issues. These problems
> can be insidious at times. For example, I've seen a lot of, even "professional
> grade" applications, where you can't reliably reproduce some setting in the
> GUI, just doe to sloppiness in implementing the stepping, increments and
> up/down window in some slider.
> While arguably "it doesn't matter" most of the time, there are situations were
> you'd need to change some setting at just one point and be sure that everything
> else is retained absolutely unaltered, without inserting, jerks, banding,
> alias noise and similar artefacts at places which you actually "did not touch".
> Still more so, since we want to build an elaborate frame cache, we should be
> able to integrate some single frames rendered during the editing process some
> weeks ago into the final render by just pulling them from the cache. This is
> not possible, unless we can be sure that re-calculation of those frames would
> yield the same result down to the last bit.
> And yes, if you stick to some very simple rules, even floating point
> calculations can be made deterministic. At least you can tell with certainty
> when a calculation will be deterministic and when will fail to be so. But
> you need to care; thus this goal is directly linked to "professionalism"
> Cheers,
> Hermann
Yes, that's as it should be.  But none of that is expressed by the 
phrase "a singlle digit".  Rather, it suggests gross quantization 
with at most ten levels of whatever, there being ten digits, and a 
resulting *lack* of precision.

-- hendrik

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