DR & DRR comparison: HDR10 vs. 8-bit + 10-bit sRGB: Photographic Science and Technology Forum: Digital Photography Review (2024)

5

quadrox wrote:

Definitions:
DR - dynamic range - number of stops between darkest and brightes value
DRR - dynamic range resolution - smallest possible difference between values

Topic: It makes sense to say e.g. that a given sensor has 13 stops of dynamic range and we know both the DR and DRR - this works well for raw images (at least theoretically).

I have always assumed that e.g. an sRGB JPEG image also has a well defined DR and DRR, meaning an ideal monitor that is capable of displaying 8bit sRGB images faithfully should always have the same number of stops between pure black and pure white, even if I may increase the overall brightness of the image.

Now we are finally getting some image standards with more bit-depths, e.g. HDR10 and whatever else they are called. These sport 10 bits instead of only 8 bits, but where do these extra bits go? Do they extend the DR, and the DRR stays the same? Do they affect both? Is this even well defined?

Both.

sRGB tone curve is described in https://en.wikipedia.org/wiki/SRGB

HDR10 uses the Perceptual Quantiser tone curve defined by SMPTE as SMPTE ST 2084

The HDR10 encoding covers a wider dynamic range with smaller step size than sRGB.

The shadow resolution (DDR) is clearer on a log/log plot:

1023 samples HDR10, 255 samples sRGB

If maximum sRGB luminance is 100 nits (cd m⁻²), then the brightness steps of HDR10 are smaller than 8 bit sRGB for luminance values less than 78 cd m⁻².

The BBC white paper quotes the Schreiber limit for the minimum perceptible brightness difference as 2% for screen luminance greater than 1 cd m⁻².

Fractional brightness step is less than 2% for HDR10 values greater than 1 cd m⁻².

For 10-bit sRGB, the fractional brightness step is less than 2% over the a range of 7.6 stops, down to 0.52 cd m⁻² (for 100 cd m⁻² maximum).

I know that even before HDR standards we have had 10bit monitors, but as far as I know these did not feature expanded DR as such, but instead offered more DRR and expanded range for colors. Now, if we want to combine this approach of expanded color spaces with the idea of expanding the DR, don't we need more than 10bits? Why is this not a thing? Indeed, why is the industry (monitors and image standards) lagging so far behind our ability to capture images with high fidelity?

According to https://www.gsmarena.com/understanding_hdr10_and_dolby_vision-news-46151.php

• The brightest mastering monitors that cost tens of thousands of dollars can go as high as 4,000 nits but most consumer televisions cannot exceed 1000 nits, with OLED models being even dimmer.

The smallest fractional intensity difference the eye can resolve, Weber's fraction varies with illumination level and is around 1% - 2% for photopic vision. At lower light levels, acuity and contrast sensitivity are poorer.

The ST 2048 PQ tone curve seems to be a decent match to the varying contrast sensitivity of the human eye. There is further discussion in the BBC document linked by Entropy512, In particular see figure 5, page 7.

T. Borer and A. Cotton, BBC R&D White Paper WHP309, A “Display Independent” High Dynamic Range Television System". http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP309.pdf

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