Text Aliasing in DCP-O-Matic

[jamesuk1981]

Hello

I have noticed burnt-in text aliasing in my videos when brought into DCP-O-Matic. Particularly bad when it is red text. The source MP4 video doesn't have the issue, but it happens when brought into DCP-O-Matic and viewed in the preview window. Sadly, it exports this aliasing into the DCP. It is text created in Premiere and/or After Effects and burnt into the video. I've noticed it on quite a few videos I have created then DCPd. Attached is a zoomed in screenshot from the source video, then a screenshot of the same frame in the DCP-O-Matic window.
Is there anything I can do to reduce this issue?

[carl]

Which version of DCP-o-matic is this with?

[Carsten]

Can you show us a frame from the actual DCP - e.g. loading the MXF into VLC and producing a VLC video snapshot?

If the master video is high res, including burnt-in text, it is hard to believe that DCP-o-matic creates that kind of scaling/aliasing during encoding.Hi contrast and saturated colors may produce some edge overshoot, but it shouldn't look so bad.

- Carsten

[StephW999]

Hi jamesuk1981,
This happens if your video is output in 4:2:0. The red is in this case is in half definition.
You must at least produce a ProRes 4:2:2 file, or best if possible in TIFF image sequence.
A DCP is not video. All sources must be uncompressed and in 4:4:4 if possible.
I also agree with what Carsten said

[jamesuk1981]

Thanks everyone for your feedback. It is the latest version of DCP-o-matic.

I have done a screengrab from the mxf file created by the DCP. Perhaps it doesn't look as bad as in the DCP-o-matic preview window but its definitely still aliasing. I had the opportunity to watch this particular DCP on the big screen recently and the text jagged effect was particularly noticeable and looked horrible Which is why I am trying to look into this issue now.

I think the 4:2:0 encoding of the MP4 is a really interesting suggestion. Thank you. I will create a ProRes file and make a DCP from that and see if it looks any better and let you know the results!

[jamesuk1981]

Hi again

So this is weird.

I exported a clip from my timeline as ProRes 4444. The red text looks lovely in VLC when the video output is set to automatic - but the image is overly cyan. When I set the video output in VLC to DirectX, the colours are more true, but the red is jagged again and looks worse than ever. When I bring it into DCP-o-matic, the text still looks awful.

I'm so confused.
James

[carl]

Can you confirm the version number of DCP-o-matic that you are using? There are two possible versions that could be called "latest".

Is it possible to make a clip which shows the problem so that I can take a look? Or make the whole video available?

[jamesuk1981]

Hi Carl

My DCPoM version is 2.16.66

First of all, I'm realising the text in my video looks very different in VLC depending on how I set the video output. Directx vs Automatic, for example.
On the ProRes 4444, I can either have lovely crisp/sharp text, but with a cyan tint using DirectX output, or accurate colours and horrid text aliasing using Automatic. I haven't tried all options yet, but will play around.

If I bring the ProRes 4444 back into Premiere, everything looks great - colours and the text - so it seems as if the ProRes export is ok.

When I bring that ProRes 4444 into DCPoM, the text is sooooo jaggedy, it looks horrid. Is there something happening with the colour reproduction/output in DCPoM that I need to change? I know this isnt just an issue with my viewing outputs on my laptop, because I noticed the issue when the DCP was projected at a cinema in London.

James

[carl]

Is there an alpha channel in the video file? If so it might look better in the latest (2.16.71) as that has a fix for DoM's alpha channel handling.

[jamesuk1981]

No alpha channel as far as I'm aware.

Here is a short ProRes 4444 export from my video.

https://www.dropbox.com/scl/fi/e4p8g6x6 ... 9leoy&dl=0

And here is a DCP created from that ProRes file.

https://www.dropbox.com/scl/fo/962u7030 ... kae93&dl=0

I think I may have solved this with making sure I export the PR4444 with 16bpc export chosen instead of 8bpc. The preview window in DCPoM still shows jagged text using this file, but looking at the mxf it has created, it doesn't look jagged any longer.

James