4K to SD conversion issues

Summersond wrote on 6/13/2016, 9:31 AM

Sorry if this has been posted previously but didnt see anything in my searches. I recently got a 4K camera and shot a dance recital in 4K 60MBPS 30FPS progressive. I needed to convert it to SD for my clients and have found that it has jaggies in the picture when rendered that are not there in the original footage. Since this is my first foray into making SD video from 4K material using Vegas Pro 11, I am asking if there is a workflow that will produce a smooth picture as pristine as the original (noting that it is just SD) that I need to follow. I did render using 29.97 LF first which was not pretty. Then I rendered to 29.97 Progressive which was better but still shows the jaggies somewhat. Any assistance would be greatly appreciated! WHen I go to shoot a wedding in 4K, I definately do NOT want the customers to have jaggies in the final product! :)

Thanks!
Dave

Comments

rs170a wrote on 6/13/2016, 2:16 PM

Dave, no idea if this is the right setting in the 4K to SD world but it works pretty well going from HD to SD.
Apply a very light gaussian blur to the desired event, usually 0.0010 in the vertical range only. Adjust the value as needed.
Good luck.

Mike

musicvid10 wrote on 6/13/2016, 3:24 PM

Posting a screenshot would help us know what you mean by "jaggie's."
In the meantime, set render properties to Best.

Summersond wrote on 6/13/2016, 3:43 PM

I will see if I can grab one. :) What it essentialy is, is the downconverting of UHD material to SD results in poorer quality video. For one thing, the pixel size is not the same which could account for some of the issue, even though I recorded and converted in progressive. I have been googling this issue and it seems to be a problem with other folks wanting to down convert to SD. When I get home, I will grab a screenshot and post. Basically, rounded edges are not necessarily smooth, especially when there is movement. ANother term I should have used instead of jaggies is aliasing.

Dave

John_Cline wrote on 6/13/2016, 5:30 PM

Yes, make sure that the render quality is set to "Best", that is the only setting which affects the quality of rescaling.

musicvid10 wrote on 6/13/2016, 5:54 PM

Summersond,
Certainly you realize that 96% of all pixels, and thus data, are LOST during downconversion from 4K to SD resolution. The losses are nonrecoverable.

PeterDuke wrote on 6/13/2016, 5:56 PM

I don't know if the de-interlace method in project properties matters in this case, but it should be set to match your source, i.e "none". Is your SD to be pseudo "interlaced" or progressive?

Summersond wrote on 6/13/2016, 7:46 PM

It is set to progressive as well. I am experimenting on rendering to HD 30P then pulling into DVDA. I did a test piece and that seemed to work ok. I will see how the complete video looks when rendering is done later. How do I add pics to show the aliasing?

Summersond wrote on 6/13/2016, 7:48 PM

Musicvid, I do. I was hoping to just get a smooth picture without aliasing. I think for now, I will shoot in HD. I think that will remove the issue I am having. No real need to shoot in 4K just yet if there are so many issues surrounding this.

fldave wrote on 6/13/2016, 10:31 PM

Try letterboxing, not stretch?

musicvid10 wrote on 6/14/2016, 12:21 PM

You are correct that shooting 4K is overkill for most consumer delivery.

What you are seeing, however, shall remain a mystery unless you choose to post a 1:1 screenshot.
"Aliasing" is a rather specific term, and down-dithering is an involved process that is not easily described with a single term. There are likely alternatives, but not without some visual cues.

If you don't want us to see your content, however, that is understandable too.

VEGAS_EricD wrote on 6/14/2016, 1:22 PM

Regarding the "Full-resolution rendering quality" setting in project properties...

Good uses bilinear scaling without integration, while Best uses bicubic scaling with integration. If you're using high-resolution stills (or video) that will be scaled down to the final output size, choosing Best can prevent artifacts.

Keep in mind choosing Best can dramatically increase rendering times.

Hope this helps.

musicvid10 wrote on 6/14/2016, 1:32 PM

Hardly dramatic -- 5 to 15% worst case, making "good" completely unnecessary for me.
But it is all speculation owing to the OPs lack of follow- through.

NCARalph wrote on 6/14/2016, 1:35 PM

I've seen really pronounced jaggies (motion artifacts) when shooting interlaced and doing zooming in post also to interlaced. Are you cropping?

Now I shoot everything in progressive and render to DVD also in progressive and have no such problems.

Summersond wrote on 6/14/2016, 7:13 PM

Musicvid, not sure how to post pics on this forum... Help! :)

Summersond wrote on 6/14/2016, 7:15 PM

Musicvid, I only render in best mode. I dont care about the increased render times, as I want them to get the best pic.
NCARalph, I will now only use progressive. Interlaced really sucks anymore and most players (or monitors) dont have issues with progressive.

Summersond wrote on 6/14/2016, 7:21 PM

Ok, here is link to pics rather then trying to post them.
https://1drv.ms/f/s!AqEzZzH-wkgG1km8DEOD2xIhULhw

dave

PeterDuke wrote on 6/14/2016, 7:38 PM

Have you tried rendering your 4K to a HD intermediate and then re-rendering it to SD?

Blurring (a form of low pass filtering) is essential before reducing resolution, otherwise you will introduce aliasing artefacts. Once resizing is done, you can then apply a modest amount of sharpening.

OldSmoke wrote on 6/14/2016, 8:16 PM

Try and apply this filter package.

It will help a little bit but SD is just not any better especially down converting 30p to 60i. I shoot anything with faster motion that has to go onto DVD in 1080 60p and results are actually very good. When shooting in 30p you loose temporal resolution which looks really bad in 60i from what I can observe from my own videos.

Here is a link to a 20sec video I just converted from 4K to DVD format. This is 4K 30p from my AX100.
Another tip is to burn a DVD-RW and test it on a player, computer monitors and their software players make even more a mess of it. Also try to render to 704x480 rather then 720x480.

Summersond wrote on 6/16/2016, 11:54 AM

Old Smoke and Peterduke, thanks for the tips. I will give them a try. In the future, I will shoot in HD as 4K right now is not necessary for my needs and has just created lots of unexpected issues. I can shoot in 60P in HD so I will experiment with 30P and 60P and see what works best for me, I do more weddings than recitals so not so much action in the wedding videos (at least during the ceremony; :) ).

musicvid10 wrote on 6/16/2016, 1:05 PM

Is the closeup showing the problem a snapshot of the Vegas preview?
If so, is the Preview window set to Best/Full, and the Project Properties set to match THAT source?
Have you tried the downsampling and render in Handbrake for comparison?

Summersond wrote on 6/18/2016, 6:10 PM

Musicvid, I saved the jpeg in best full mode. I have not used handbrake yet. I am rendering the project using the preset that was suggested above from OldSmoke and see how that looks rendered. Sorry for the delays in response. I have been away from the office off and on for the last few and next few days. One question I have is this - of one changes the pixel size for rendering, I wonder if that would make a difference, as pixel sizes are different for UHD and SD NTSC DV.

musicvid10 wrote on 6/18/2016, 6:29 PM

If you can upload 10-30 seconds of the original 4k somewhere (not Youtube), I'll download it and try to duplicate your results, time permitting, of course,

Summersond wrote on 6/21/2016, 7:31 PM

Musicvid, I uploaded a 30 second clip from the 4K file. Here is the link
https://1drv.ms/f/s!AqEzZzH-wkgG1kMsWUuFcmKyG9G2
Also regarding my statement of pixel size in the previous post, I meant to say Pixel aspect ratio, not size.

john_dennis wrote on 6/21/2016, 8:09 PM

If you're happy that this file doesn't have the artifacts that you experienced, I'll explain how I did it.