Error in HLG HDR appendix step 8

[nigelmegitt]

Step 8 of appendix Q.2 Hybrid Log-Gamma HDR currently says (third line):

and b = 1−4a and c = 0.5−a•ln(4a)5b

The superscript 5b at the end is a transcription error from BT.2100, in which the 5b is a footnote reference (in an equation!).

The line should be:

and b = 1−4a and c = 0.5−a•ln(4a)

i.e. the superscript 5b needs to be removed.

[nigelmegitt]

Here is the updated submission document to the one attached previously at #233 (comment) with the bug fixed there too:

SimpleConversion_sRGBtoHLG.pdf

[nigelmegitt]

An additional point here is that in step 8 the line above the one highlighted in the issue is confusing:

where HLG(x) = (3x)0.5 if 0 ≤ x ≤ 1/12 or HLG(x) = a•ln(12x−b)+c if x > 1/12 and a = 0.17883277

This would be clearer if the "if"s the "and"s and the "or"s were separated out better.

[nigelmegitt]

The same issue arises for step 11:

where clamp(x) = x if 0 ≤ x ≤ 1023 or 0 if x < 0 or 1023 if x > 1023

[nigelmegitt]

I see that we have non-aligned syntaxes for the definitions of clamp in Q.1 and Q.2; also the formatting in Q.1 doesn't use preformatted blocks for the mathematical expressions, which it should to be aligned. Will throw fixes for that into the PR too.

[nigelmegitt]

PR #398 updated to address the above three additional comments.

[css-meeting-bot]

The Working Group just discussed ttml2#397 Error in HLG HDR appendix step 8.

The full IRC log of that discussion

<nigel> Topic: ttml2#397 Error in HLG HDR appendix step 8
<nigel> github: https://github.com//issues/397
<nigel> Glenn: I merged #398 without any changes except to remove the HTML generated version.
<nigel> Nigel: Thank you, I always include that for easier previewing.