GH4 GH4 Downsample 4K to 1080p 10-bit 4:4:4

J

Jlippencott

Member
From what I have been reading it's not just possible, but easy to downsample 4K footage to 1080p 10-bit 4:4:4 as per article:

http://www.eoshd.com/2014/02/discovery-4k-8bit-420-panasonic-gh4-converts-1080p-10bit-444/

Near the end of the article there is a question and answer about the method:

Q - Will it require specialised software to do the transcoding and downsampling? or can existing methods be used?
A - As long as you upconvert to RGB and 10/16-bit first, you get the benefits. A 16-bit comp can demonstrate this to be all true.

When I drop a 4K Clip into a 1080p timeline in Premiere I get a gorgeous result, but the render is still 4:2:0.

I am new to all this and do not really know what they are saying. How do I upconvert? What's a 16-bit comp?
Can anyone here help with the details?

I posted to the authority above looking for an answer, but there were no replies.
I see lots of topics on the web telling people what to do, but not how to do it.

Thanks
Joe
 
Jlippencott said:
When I drop a 4K Clip into a 1080p timeline in Premiere I get a gorgeous result, but the render is still 4:2:0.
Click to expand...

Like Mike said, the timeline will be 4:4:4, however it won't be RGB as required to get the 'benefits' of the downsampling. PP will keep the footage in the YUV format until forced not to. As a general philosophy, this is actually a good thing.

My own plan is to convert the footage before editing using Prelude to a DNxHD 444 format. This has two advantages. First, I get the RGB 444 that I'm looking for, and second, DNx edits a WHOLE lot smoother an H.264 media. The downside is that the new media will be 1080 and not allow for any kind of reframing or 4K delivery, but if those things aren't important to your workflow, give it a try.
 
I'm sticking with 1080 for now since that's the norm until 4K viewing gear gets more common and a LOT cheaper.
I don't have any means to view anything 4K anyway and don't know anyone who does.

I wasn't aware that Prelude did conversion. I'll have to look into that.
I will also look into the rendering options to see what's available. I wish I knew more about the details - the permutations are mind boggling.
I would of course save the original 4K file for the future.
That's one thing I like about the GH4 - it's "Future-proof" to some extent.

Thanks very much
 
Hello Jim,
I cant seem to find DNxHD 444 in the transcode list for Prelude or for Media encoder, either.
I am running CS6. Is this a CC only capability?
 
Shooting 1080 on the GH4 line-skips. You get a much more detailed image, if that is your goal, shooting in 4K and down-converting to 1080.
 
Mike Warren said:
Are you sure? I understood no line skipping was a headline feature on the GH4.
Click to expand...
In 1080, it definitely does. In 4K it doesn't, but in 1080 it does.

Perhaps you're confusing it with the HC-X1000, which uses the same venus engines and the same recording formats for 4K, but specifically doesn't do any line skipping. It has two processing engines in it, so it creates its 1080 from a full and proper downscaling of the entire 4K chip.

The GH4 doesn't have the ability to read its chip at 60fps, at native size. So to get 60fps, it has to skip lines.
 
Not sure, but folks have posted moire tests that show that it's definitely doing skipping. If you want great 1080p from a GH4, the best way to get it is to downconvert the 4K (although that doesn't help if what you need is 60p or 60i, of course).
 
I think where there is confusion is how much better the line skipping in the GH cameras is compared to the line skipping in Canon cameras. Panasonic does it so well compared to the others that one would assume there is no line skipping. It is still line skipping but light years better looking than the line skipping on other cameras. The GH2 used the same method to record a 1080p video form a 4k sensor and that camera was widely considered most excellent in terms of quality. HD from the GH4 is just as good if not better and I would hardly call it not good enough for serious production work. HD from the GH cameras has widely been considered professional for a very long time now.

4k down converted makes for a cleaner image but shooting HD is still a phenomenal level of quality on the GH4. Still beats the pants off of most HD cameras out there.
 
In regards to using Prelude for down conversion I would be a bit careful with that. As far as I know this conversion happens at 8 bits. Premiere (which basically means the engine Prelude uses) works in 8 bit color space unless a filter calls for 32 bit float processing. So it really only works in 32 bit float color space when you apply a filter like color correction or keying.

A better tool to use is Adobe After Effects which can be set to always use 16 bits for the project you are working on. This way no matter what you do your material will be processed in a 16 bit per channel environment which is more than enough to try to increase the bit depth during a down conversion. After Effects also does a really good job at filtering the 4:2:0 chroma in the 4k footage and turn it into a smoothed 4:4:4 before down conversion. This may give you a tiny bit better averaged result when down converting the 4k material to HD compared to just slapping it in a 1080p timeline in Premiere. After Effects also has a pretty decent noise reduction filter that can be used to remove noise from the 4k material before you down convert to HD. It is better to remove noise before you down convert because the down conversion process can help retrieve lost detail from the noise reduction.

Using After Effects may be a slower process but in the end I think it yields the best quality.
 
I can get most of what I need from CS6.
I think CC is very nice, but I also think it's extortion - if you don't pay your monthly fee, you lose all your capability.
I would rather know my software is permanent and local than take the chance of losing it.
Maybe someday when I get well off enough to afford it, and the cost doesn't matter as much, I will switch over.
 
Jlippencott said:
I can get most of what I need from CS6.
I think CC is very nice, but I also think it's extortion - if you don't pay your monthly fee, you lose all your capability.
I would rather know my software is permanent and local than take the chance of losing it.
Maybe someday when I get well off enough to afford it, and the cost doesn't matter as much, I will switch over.
Click to expand...

While I'm not a fan of subscription models, I will say the $360 I pay a year for EVERYTHING Adobe has, is much cheaper in my mind than the $800 somebody pays for just the privilege of "owning" AKA being stuck with Premiere Pro CS6, which is frozen in time.

If this is a hobby then by all means use whatever. But if this is a business, and the $30 a month added to the cost of doing business is too much, then you are in the wrong business.

All the best!

Dave
 
I normally use Premiere for editing only - getting my timeline where I want it, then export to AE for color correction and grading.
From what I understand, a 4K file on a 1080 timeline in PP is 10-bit 4:4:4 (if done right).
When I export to AE, am I getting the benefit of the chroma subsampling and bit depth there (if I have AE set to 16 or 32-bit)?
 
It is a hobby now that may eventually grow into a business. That would be when I consider the monthly cost.
My expenses all come from the household budget for now.
 
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