Image artifacts with Doremi IMB-4K / ShowVault

[Pietro Clarici]

Hello,

I have been experiencing some issues with 4K material (macroblocking, small flashes, and so on) on a Doremi IMB-4K / ShowVault setup running in a NEC 3240S projector.
They are happening right now with "Poor Things", but we've seen this sporadically with Oppenheimer and other 4K content, while 2K material does not seem to be affected.
We are running the latest software updates, but we've been told by the local distributor that this is apparently a known problem with Doremi servers, and that we should downgrade to 30.07z - which is strange since 30.11a, the next firmware version, seems to target this specific issue according to changelog.

However, can anyone confirm that downgrading from 30.11g to 30.07z will actually fix this?
But more importantly, is firmware downgrade still a safe option after the "Y2K24" Security Manager updates?

[Harold Hallikainen]

https://www.isdcf.com/wp-content/upl...TED.pdf#page=4 has the ISDCF discussion on the 4k image issues.

Harold

[James Gardiner]

Such issues should be reported back up the chain. As DCI/Deluxe etc are looking to collect more data on all issues like this.

From my understanding, a document should eventually come out with more detail on such issues. Surprised it is not out already. Keep an eye out for future ISDCF meeting notes.

[Steve Guttag]

I would also contact Dolby/Doremi to report the issue and seek their advice on the best software set to use in your application that is consistent with the new certificate expiration date.

[Randy Stankey]

Just a thought... Could this be a side effect of the Y2K24 bug and the patches that were issued to fix it?

Could it be that, somehow, because of some extra work that the processor has to do, working around the date bug, the decoder can't keep up and has to "dump its load," so to speak, before it's time to go to the next frame or else the whole picture will drop out?

I don't know if this is really true. It just seems like a strange coincidence.

These days, it's getting all too common for companies to "just patch the problem" without considering the possibility of unintended consequences, down the line, thinking, "We'll worry about that later."

[Pietro Clarici]

Thanks, it's definitely worse than I thought if even ISDCF is still trying to figure it out.
I have already contacted the distributor about this, I'm applying for the third time to access Dolby Customer portal (got denied twice for some reason), if it doesn't work I'll try and reach them through my dealer.
I don't think it is related to the patches because it was happening even before the SM update.

[Randy Stankey]

I don't think it is related to the patches because it was happening even before the SM update.

If it happened before, it's likely not the problem. Just a thought...

[Harold Hallikainen]

According to what I've heard in ISDCF meetings, and I think is stated in the previous link, the issue is with the JPEG decoders in some older equipment. I THINK this equipment used a decoder chip instead of an FPGA to do the decoding, so it cannot be updated. There is software to check for one of the issues (the 0xff issue), but the other issues have not, as far as I know, been truly identified. I understand this occurs mainly (only?) on 4k content. A distributor fix MIGHT be to have a 2k version to send to theaters with the issue.

Harold

[Carsten Kurz]

We discussed the specific Doremi IMB 4k weakness a long time ago, I did some animated test sequences then to break the 4k decoding, which then causes flashing artefacts:

http://www.film-tech.com/cgi-bin/ubb...002306/p5.html

This is different from the Dolby DSS200/CAT862 4k ('MI-7') color halo issues that came up recently (but had been seen occasionally in earlier years already)

I guess those issues with 4k show up more often nowadays simply because we see much more 4k content in distribution today than we saw back then.


I think firmware downgrade is okay, the Y2K24 issue is a security manager issue, which is separate software, and the cert expiration will only happen at the end of 2025, which leaves time for some testing. But you may reconfirm this with Dolby.

[Pietro Clarici]

Thanks. The strange thing is that we installed this projector/IMB combo in 2013, we played a lot of 4K material and neither I nor my team remember any issues before last year - except some heavy artifacts with the very first software release which went away after a few months and a couple of updates. That's why I was wondering if there was general knowledge of a specific Dolby firmware triggering it, or maybe something to do with recent DCP authoring software. Seems to be much more deeply rooted than that.

[Carsten Kurz]

It is also dependent on actual 4k image complexity. So, it may occur in some highly detailed sequences only, but not generally with 4k DCPs.

[Pietro Clarici]

Quick update: I have not been able to reach Dolby yet. However, as a temporary solution I found out that there are no glitches if the server only decodes the 2K part of the 4K JPEG2000 stream, so I’m forcing the IMB to play in 2K and using specific screen files on my projector to upscale the output to 4K. Not ideal, but it’ll do for now.

[Carsten Kurz]

That's true, the glitches occur when the IMB falls back to 2k decoding. If you force it to 2k, you should be fine.

[Fabian Schreyer]

I just want to add that we are experiencing these issues as described by Pietro with a Doremi IMB/ShowVault/CP4230 configuration. Most of the time it is macroblocking/short flashes several times during the show (and probably only with 4K content).

I have read the linked ISDCF document and while it sounds similar at first glance, the specific issues seem different to what we are experiencing here. Carsten pointed this out, but I do not agree that it might simply be caused by the presence more 4K content. We showed a lot of 4K content several years ago and never did anything like that happen.

[Marco Giustini]

Fabian,
those servers are clearly compatible with 4K but the encoders/machines have meanwhile changed/upgraded in Post Production and there is something the Doremi decoders cannot handle now.