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Re: [csswg-drafts] [css-color-hdr-1] Compositing SDR in HDR outputs (#5323)

From: simontWork via GitHub <sysbot+gh@w3.org>
Date: Tue, 15 Dec 2020 15:15:38 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-745357411-1608045294-sysbot+gh@w3.org>

> So, that requires re-rendering of the SDR image? Also, we are talking about scaling a linear-light image not a gamma-encoded image, right?

The effect of a specular highlight on the midtones depends on its size and distance from the midtone of interest.  So it's not something that can be easily accounted for in static transform.  It's best seen by looking at an HDR and SDR copy of the same image.  The overall eye adaptation is related more to the average light level and the surround than the specular highlights.

As for expanding the highlights, many SDR video cameras have a "knee" which compresses the highlights to give some details as opposed to clipping.  Some transforms do some expansion - there's quite a few methods in literature, patents etc.

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