Testing for HD Broadcast

[Bill Weaver]

I'm running the XF300 through lots of compression to see how it performs, testing for shimmer, etc. Playing with 24p.

Apple TV export is a good way to take a gander at footage through a popular download medium. Even at -7 sharpening, there was stil some shimmering and moire showing up after compression. Shimmering all but disappeared with the sharpening off.

What's the best compression to run video through to test how it would perform if broadcast/cablecast?

[Bo Sundvall]

Hi

I've read about this shimmering in other posts. Is it possible for someone to post a link to some video where this phenomenon can be seen?

Regards,

/Bo

[Lou Bruno]

The shimmering is impossible to observe on any UPLOADS to the internet. It prevails on a HDTV and when compressed to AVCHD.

I have my sharpening set all the way down on the HDTV. I will also try taking the sharpening off all together on the camera. The interline twitter is either the sharpness of the lens, the processing of the signal or both. Having a HDTV set to a high level of sharpness does not help either.

[Bill Weaver]

I'm begging to see that it's a really variable factor, depending on codec, sharpening, resolution of TVs. I was watching a PBS drama last night that was shot either on film or RED, and I saw shimmering in detail there as well. (Of course, I was looking for it. But because it was shot cinematically, the BG was soft most of the time, so less chance of shimmer or moire).

[Antony Michael Wilson]

Bill, are you scaling your images when you render for Apple TV? Doesn't Apple TV work at 720p? If you're shooting 1080 for 720 delivery, scaling is a likely culprit for the aliasing you are seeing - both on the encode and the display (a 1080 TV will use its own poor quality scaling to bump up to 1080 again). A good sharp 1080 image will need a high quality scaling algorithm to create a 720 or SD down-convert. I can get very smooth/sharp images from the 305, which alias like crazy on 720 and SD down-converts even before any TV set re-scaling (and inevitable aliasing) is added on top. We use Teranex hardware to do downconverts with excellent results from 305 footage shot with detail set to -7 (progressive).

[Charles W. Hull]

Originally Posted by Lou Bruno

The shimmering is impossible to observe on any UPLOADS to the internet. It prevails on a HDTV and when compressed to AVCHD.

Do you also see this with mpeg2? Does it have something to do with H.264?

[Lou Bruno]

Yes, it is observed directly from the camera via HDMI. However, compression magnifies the interline twitter. A few good examples are firne tree branches, brick work and chain link fencing.

[Bill Weaver]

Originally Posted by Antony Michael Wilson

Bill, are you scaling your images when you render for Apple TV? Doesn't Apple TV work at 720p? If you're shooting 1080 for 720 delivery, scaling is a likely culprit for the aliasing you are seeing - both on the encode and the display (a 1080 TV will use its own poor quality scaling to bump up to 1080 again). A good sharp 1080 image will need a high quality scaling algorithm to create a 720 or SD down-convert. I can get very smooth/sharp images from the 305, which alias like crazy on 720 and SD down-converts even before any TV set re-scaling (and inevitable aliasing) is added on top. We use Terranex hardware to do downconverts with excellent results from 305 footage shot with detail set to -7 (progressive).

Interesting. I'm watching on an older 720 HDTV.

[Antony Michael Wilson]

Did you establish if the Apple TV encode is scaling down to 720p? It would be interesting to get to the bottom of your issues here and I think it's important to eliminate any post/display device scaling because that is the single most prevalent culprit for aliasing on television viewed in the home. If something is shot on a super-sharp device like the 305 - even assuming all native/baked in aliasing is removed by dialing back artificial edge enhancement/sharpening in camera - all scaling to the point of delivery will need to be performed well for there to be an absolute absence of aliasing. Unfortunately, most software is terrible at scaling and domestic TV sets are usually even worse. If your HDTV set is 720p, then in order for you to see alias free images derived from the 305 filming native (i.e. 1080p) set to correct sharpening levels (I think we all agree this means minus 7 or lower) you will need to perform a 1080 to 720 down-conversion at high quality. How are you performing the encode to Apple TV? If you're actually filming at 720p then it would be very hard to achieve an alias-free image to begin with because the camera is rather poor at the down-convert to 720p from the native 1080 raster.

This is an issue we have looked at long and hard with the XF because - no matter how stellar the 1080 images the camera produces - one does need to be able to produce 720p and SD deliverables that are sharp and clean. FWIW the default sharpening even of the Avid DX hardware on down-converts is far too high and will introduce hefty aliasing even from XF images that display fine on a 1080i monitor (p over i). AJA hardware is much better but still not perfect. Better hardware allows you to customise sharpening levels, so you can figure out a custom preset that works. Obviously, we're just lucky we have the Teranex, which is almost as expensive as the camera itself!

All good quality down-conversion (particularly to SD) will require some degree of edge enhancement/sharpening for the image to appear sharp enough. It's just a real problem when you're starting with 1080 images that do really approach max resolution with fine detail involved where the tool involved (software or hardware) does not give you control of the sharpening or just uses simple line scaling or a poor algorithm. I've found that After Effects does a rather nice job of scaling and so does the now defunct Liquid.

I hope this helps in some way. If you like, I'd be happy to take a look at some of your shots and see if I can figure out if the issue is inherent to the footage or just the result of a scaling problem in the post/delivery process. PM me if you need to.

[Bill Weaver]

Yikes. This is so complex. I so want to just shoot and deliver. I have used XDCam HD (VBR) and XF footage in the past, and have not experienced this degree of complexity.

I have done software conversions to Apple TV (720) via export from FCP, via compressor, via Quicktime 7 using two passes, and via Adobe Media Encoder.

Camera is shooting 24p at 1080, with sharpening at -8, coring at 5, HV Bal at 5, an Sel at 15 (basically modified "Mojo" setting)

Moire is barely visible on downconvert, played on on 720 HDTV.

But the bigger question for me is, is it going to take a lot of post production processing to make this camera work in the real world? Or is this just a day in the life of any high res camera?

I'm trying to plan several project across different mediums, and the more I explore, the more questions there are.....

Originally Posted by Antony Michael Wilson

Did you establish if the Apple TV encode is scaling down to 720p? It would be interesting to get to the bottom of your issues here and I think it's important to eliminate any post/display device scaling because that is the single most prevalent culprit for aliasing on television viewed in the home. If something is shot on a super-sharp device like the 305 - even assuming all native/baked in aliasing is removed by dialing back artificial edge enhancement/sharpening in camera - all scaling to the point of delivery will need to be performed well for there to be an absolute absence of aliasing. Unfortunately, most software is terrible at scaling and domestic TV sets are usually even worse. If your HDTV set is 720p, then in order for you to see alias free images derived from the 305 filming native (i.e. 1080p) set to correct sharpening levels (I think we all agree this means minus 7 or lower) you will need to perform a 1080 to 720 down-conversion at high quality. How are you performing the encode to Apple TV? If you're actually filming at 720p then it would be very hard to achieve an alias-free image to begin with because the camera is rather poor at the down-convert to 720p from the native 1080 raster.

This is an issue we have looked at long and hard with the XF because - no matter how stellar the 1080 images the camera produces - one does need to be able to produce 720p and SD deliverables that are sharp and clean. FWIW the default sharpening even of the Avid DX hardware on down-converts is far too high and will introduce hefty aliasing even from XF images that display fine on a 1080i monitor (p over i). AJA hardware is much better but still not perfect. Better hardware allows you to customise sharpening levels, so you can figure out a custom preset that works. Obviously, we're just lucky we have the Teranex, which is almost as expensive as the camera itself!

All good quality down-conversion (particularly to SD) will require some degree of edge enhancement/sharpening for the image to appear sharp enough. It's just a real problem when you're starting with 1080 images that do really approach max resolution with fine detail involved where the tool involved (software or hardware) does not give you control of the sharpening or just uses simple line scaling or a poor algorithm. I've found that After Effects does a rather nice job of scaling and so does the now defunct Liquid.

I hope this helps in some way. If you like, I'd be happy to take a look at some of your shots and see if I can figure out if the issue is inherent to the footage or just the result of a scaling problem in the post/delivery process. PM me if you need to.

[Antony Michael Wilson]

I know what you mean, Bill. It's a pain in the neck. To be honest, it's not actually that complex - it's just that too many of the software and hardware tools in the industry just aren't that great and need to catch up. It's just a question of finding the right solution at the right price and then you won't have to think about it again. For example, Liquid (now dead) wasn't expensive and was absolutely brilliant for scaling control and sub-pixel processing. FCP and Avid are both poor and Compressor only works reasonably well with custom controls, which take an age to encode.

Don't worry about the camera, though. It's good. I've had similar issues with the EX1/3, which is the other obvious example of a relatively cheap camera that does produce deep focus detailed footage close to max 1080 resolution.

You just need to get an alias-free image at the cameras native resolution, then find the appropriate tool to perform down-conversion and quite likely a third for encoding. The only solutions that do all this properly and fast (i.e. real-time) are hardware-based and this is an example of why there's still a healthy market for products from the likes of Snell and Teranex.

[Bill Weaver]

Good thoughts, Michael...

For those of us without access to the high-end processing tools, it would be great to compile a list of software-based solutions / techniques that will insure the best from this camera when it is finally viewed by an audience.

We know what we can spend on the high-end, but for those of us who choose more parsimonious paths:

*best camera settings
*best software for compression, etc. and how to use them to their potential
*best consumer HDTVs for edit suites (I know we really need true monitors, but what are best compromises)

I'm sure there is information even in the DVinfo fourm, even in this subforum -- but how nice to have a white paper of sorts for this group with links to relevant articles, such has this one from the Ken Stone site:

Preprocessing in Compressor and Episode