[opendtv] Re: Sparkle

From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
Date: Wed, 7 Dec 2016 05:18:56 +0000

Craig Birkmaier wrote:

This paper does a good job of explaining the issues:

http://files.spectracal.com/Documents/White%20Papers/HDR_Demystified.pdf

Excellent source of real information. And quite a bit to digest, so many
thanks, Craig.

Please read the section on HDR Transfer Function.

In my first read, it looks like the new SMPTE ST2084 quantizes luminance in an
absolute way, not relative as in BT.709. So the maximum value does not map to
the maximum brightness of any given display. Instead, whatever value must map
to an absolute brightness level in each display.

This paper says that a 10-bit value of 691 maps to 500 nits. Assuming these
numbers are integers, that would be

10-1011-0011

which leaves room for expansion. And then, any given display will have to
process brightness levels outside its capabilities to best render the image.

So I give you this one, Craig. With ST2084 mapping, 10 bits are enough for HDR
luminance. The important quotes are below.

Bert

"The SMPTE ST2084 EOTF curve is a 10 or 12-bit quantization of absolute
brightness. It is an absolute luminance function, requiring the EOTF of the
playback display to exactly match the EOTF of the mastering reference display.
The ST2084 EOTF was designed with headroom for future expansion and covers a
range of luminance from 0.00005 nits up to 10,000 nits (figure 3). ST2084 maps
each video signal code word to the same absolute luminance and chromaticity in
every display (i.e. 10-bit code word 691 always maps to 500 nits). This allows
each playback display to exactly match the luminance and chromaticity of the
mastering reference display."

"Since SMPTE ST2084 corresponds closely to the human perceptual model, it makes
the most efficient use of signal bits throughout the entire luminance range. An
ST2084 encoded signal can represent luminance levels up to 10,000 nits at the
cost of relatively few extra code words (figure 3). A majority of the ST2084
codes represent lower luminance levels, to complement the human visual system's
greater contrast sensitivity at lower luminance levels and to minimize visible
banding at those lower levels. Half of the HDR codes are in the SDR range,
meaning that 10-bit HDR doubles the number of code values in the SDR range,
compared to traditional 8-bit video."

"To optimize the images, an S-curve function is used to map scene light to
display light. This Optical to Optical Transfer Function (OOTF - often referred
to as rendering intent or system gamma) compresses/clips the extreme highlights
and dark areas and contrast enhances the mid-range light levels with a gamma >1
characteristic (typically 1.1 to 1.6). The SMPTE ST2084 PQ system, which is
defined by its EOTF, was designed to have the OOTF applied in the camera or the
production process (figure 4)."

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[opendtv] Re: Sparkle

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