During the Antenna man interview with Madeleine Noland, president of the Advanced Television Systems Committee, she mentioned that Sinclair has implemented HDR on all of their ATSC 3.0 broadcasts. I don’t have any ATSC 3.0 receivers so I can’t verify this. Can someone who is using ATSC 3.0 in a Sinclair market check out whether they are using HDR.
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I received the following answer from the Silicondust atsc 3.0 forum. It is very interesting.
All ATSC 3.0 video broadcasts are currently HEVC with AC-4 audio, so nothing new there. What Dweber3 is asking about is the fact that Sinclair-owned broadcast stations are now encoding their content with SL-HDR1 (aka 'Technicolor HDR') metadata added. Sinclair claims
that they've launched this with 36 stations, as of Jan 05, 2023. Based on a quick review of my local Sinclair-owned station here in Raleigh, NC, I can confirm that, at a very minimum, the metadata for SL-HDR1 on CW22 is indeed present.
The primary issue with the Technicolor HDR format though is that it was largely abandoned by most TV manufacturers a few years ago (for instance, LG dropped official firmware support in their 2021 models), presumably because Technicolor finalized SL-HDR1 in 2016 or so, and yet there had been no major deployments of it in the real broadcast world (I think one niche European broadcast channel utilized it). LG was probably Technicolor's biggest supporter of SL-HDR1 with their high-end OLED TVs from 2017-2020, but tmk, no major TV manufacturer has enabled SL-HDR1 support in their 2021 and 2022 TV models. TCL made a big announcement at CES that their high-end miniLED 2023 TVs would support SL-HDR1, and it remains to be seen if that will come to fruition (my guess is that it will).
Even though the adoption of SL-HDR1 has been very slow, the primary reason for it's existence is two-fold: First, it can be delivered as one primary stream to both SDR and HDR TVs. SL-HDR1 is capable of dynamic metadata similar to Dolby Vision and HDR10+, but unlike those two formats, the base layer for SL-HDR1 is actually 8-bit SDR. Therefore, when a channel with SL-HDR1 is viewed on a SDR-only display, or a non-SL-HDR1-compliant HDR display, only the 8-bit SDR-graded picture will be shown. The result of this is that there should be no noticeable difference in the image, contrast, and color quality of this decoding compared to traditional SDR channels. The second advantage is that in contrast to the HLG HDR format, which also shoots for similar general compatibility, SL-HDR1's approach can deliver much more dynamic color and contrast when in true HDR mode. A true HDR source converted to SL-HDR1 for broadcast and then properly decoded back in HDR should look very similar to the original source in terms of color and contrast. This is dissimilar to HLG, as HLG generally looks less 'HDR-like' in HDR mode (in my experience, only the luma is truly somewhat equivalent), and not as professionally graded when decoded in SDR mode. The metadata in SL-HDR1 can even upconvert standard SDR to HDR with minimal interaction from the broadcaster, although the effectiveness of this is only going to be as good as the LUT applied, and probably no better than what most higher-end TVs are already capable of when placed into their internal SDR-to-faux-HDR picture modes.
Unfortunately, none of the TVs I have natively support SL-HDR1 for me to be able to verify the exact approach Sinclair is taking with this current broadcasting. Whether they are just passing basic metadata or attempting to do an HDR upconversion is unknown. A basic metadata passthrough, even with all colors residing within the Rec 709 colorspace, could have some value in assisting a TV with more accurate picture decoding. This is something that I've seen done in some Dolby Vision demos, and it results in a far superior and much more accurate image that I've always wondered why Dolby didn't promote it more. I seriously doubt that Sinclair is actually sourcing any content in native HDR right now. From a look at the stations they own, these seem to be mostly ABC, FOX, CW, and meTV affiliates, and none of these major broadcasters have a HDR distribution path today. Sinclair has a HDR distribution path for the regional RSNs that they own, but I doubt any of that content is being simulcast to the OTA.