[Lumiera] a single digit??

Ichthyostega prg at ichthyostega.de
Thu Feb 7 20:53:09 CET 2013

Hello Hendrik,

just saw you placed a question/annotation some time ago:

        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"


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