William F Pokorny <ano### [at] anonymousorg> wrote:
>
> 709   - Rec 709. The default setting for the povr branch. The
> recommendation is aimed at HDTVs with standard dynamic range.  Most
> correct at an assumed_gamma of 1.0 and very near sRGB.  The best general
> choice for v3.8 (povr).
>

There is something about the REC 709 standard that has confused me for quite
awhile, in a general way. (I'm probably going off-topic here). AFAIU, it is a
standard for video capture and display, so I'm not sure that I understand how it
relates to color -> grayscale conversion within your povr branch (as for
height_field use.)

But my real confusion concerns POV-ray renders made into animations.

In the Wikipedia article, it says:
"Rec. 709 and sRGB share the same primary chromaticities and white point
chromaticity; however, sRGB is explicitly output (display) referred with an
equivalent gamma of 2.2..."

"Rec 709 defines an RGB encoding and a YCBCR encoding, each with either 8 bits
or 10 bits per sample in each color channel. In the 8-bit encoding the R, B, G,
and Y channels have a nominal range of [16..235]...with 128 as the neutral
value. So in limited range RGB reference black is (16, 16, 16) and reference
white is (235, 235, 235)... Values outside the nominal ranges are allowed, but
typically they would be clamped for broadcast or for display."

Is this *the* REC 709 standard? Or is there an 'unlimited' version that
preserves the full 0...255 range? I haven't yet found an unqualified answer.

So as I understand things, when I create a typical color POV-ray image render
(as either .png or .jpg) and with the output encoding as sRGB which I use within
POV-ray, that *by itself* preserves color/brightness values from 0-255 when
decoded. But when it is displayed on a monitor that is set up with the REC 709
standard(?) (vs. sRGB?), the colors/brightness values are restricted to
16...235, with the 'outside' values clamped. (BTW, I do understand some of the
reasons for that.)

Am I correct so far?

But my main confusion concerns this:
For converting POV-ray renders to animation, I use the old but updated
'VirtualDub2 MOD' app. It works well for my purposes-- but gives me a *choice*
between using REC 709 or REC 709-R (the 'restricted' 16...235 range) for the
output encoding. According to how I read the Wikipedia article, the 'plain'
REC709 *is* the restricted version(?). Yet I do see visual differences between
the two schemes, when played back in my various apps: The 'plain' REC 709
animation does not match my POV-ray preview images (increased contrast and/or
different gamma) whereas REC 709-R does. That's a real mystery.

Perhaps this visual difference is totally due to my computer monitor itself; I
don't know.

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