Getting to grips with HDV's higher quality

[John Poore]

I have to admit I did not buy my FX1 for the HDV, I brought it to use as a 16:9 dv camera and because it was a vast upgrade over the PD-170. I should add most of what I shoot is news and current affairs stuff so I have been rather suspicious of the effects of heavy compression. I've been reading this forum regularly and have become aware of many apparent benefits of shooting in HDV then downconverting in-camera for use as SD DV. It is said here often by credible people who do know what they are talking about that this procedure creates an image that has less noise and more clarity. I have now carried out a number of experiments, shooting a shot in DV and then the same shot in HDV, which is then downconverted incamera. I have been comparing the shots to see if I can notice a difference, I've been blowing them up to examine detail and simply putting them side by side. Now the compression is not a huge problem, but I can't see a grain of difference in the actual quality. I don't wish to disparage the opinions of those who know more than me here, but is there some kind of experiment I can do to be able to SEE the difference. I want to be convinced there's a basic quality advantage to shooting SD in HDV?

[Boyd Ostroff]

All I can offer is the quick test that I did which convinced me that the downconverted footage was better. I shot a few minutes of the same scene locked down on a tripod in both DV and HDV modes. Then I captured both clips as DV using FCP.

If you use a PC the details will be a little different, but the technique should be pretty much the same. I put each clip on a separate layer in the timeline. On clip A I used FCP's crop parameter in the motion tab of the viewer to cut the left side of the image out. On clip B I did the same thing. Then I dragged clip B to the left edge of the frame.

The result was a screen split down the center which had the right half of clip A on the right side and the right half of clip B on the left side. So in other words, I could watch half of clip A and the same half of clip B simultaneously. In looking at still frames this way I could see a slight improvement in the HDV clip, but not a lot. However when I viewed the two clips in motion simultaneously the difference was much more apparent.

Try this sort of test and see what you think. Be sure that you shoot in full manual mode and that the shutter speed, iris and gain settings are identical in both clips.

[Graeme Brown]

Haven't tried it myself on the Z1, but the BBC did extensive testing and came to the conclusion that there was no quality advantage to be had. With the possibility of dropouts being higher with HDV I resolved to shoot SD unless I actually needed HD.

[Boyd Ostroff]

I'm just *guessing* here that the quality difference when shootiing in PAL (50i) mode may not be so noticeable as it is in NTSC (60i) mode since you're working with 96 more scan lines to start with.

Whenever I have a question about this sort of thing I like to read everything I can find on the topic. However, if I really want to know the answer, and if there's a simple experiment which can be devised, then I do a test myself.

With all due respect Graeme, John asked "is there some kind of experiment I can do to be able to SEE the difference". He may very well conclude that there isn't any advantage to shooting in HDV mode, but that will be based on his own observation and not something he read on the internet...

[Richard Entwistle]

Originally Posted by Graeme Brown

... ... came to the conclusion that there was no quality advantage to be had. With the possibility of dropouts being higher with HDV I resolved to shoot SD unless I actually needed HD.

I agree Graeme,

I asked a question earlier about switching tapes between DigitalMaster (when shooting HDV) and Sony Premium (when shooting DVCAM) as I have the same thinking on dropouts. Don't want a 15 frame freeze at the HDV supply side causing same freeze on a DV master/edit.

My question never got answered, but what do you think? Do you still use the DigitalMaster tape for SD?? Would switching tapes be a bad thing? Usually taboo, but DigiMaster is rather expensive for olde worlde DV recording. :)

I am about to do similar HDV/DV tests to most likely (it seems) confirm sticking with SD on some projects. It also lowers the load on my Z1 with less need for running tapes just to downconvert.

Best regards,
Richard

[Graeme Brown]

Boyd - you may be correct about the PAL vs NTSC comparison, hadn't thought of that.

Richard - I have run about 100 hours of SD through my two Z1's using exclusively Sony Premium mini-dv casettes. So far I've had no issues, but I haven't tried them on HDV. Haven't ever used anything else in the camera, and I am wary of doing so (whether it's justified or not I have no idea)

[John Poore]

Yep I am not seeing the difference as yet. It could well be exclusive to NTSC. Then again there is the issue of downconverts via software. Douglas Spotted Eagle swears Vegas makes a difference, but I would not want to buy Vegas just try this out on PAL. It would be interesting to see if Vegas can make a noticable difference to PAL footage, anyone here got a line on this? The BBC say expensive tape decks will make a difference as well, but I have yet to meet anyone here in London who is advertising this service, which is what normally happens with this kind of thing, so maybe there's little benefit to be had from PAL HDV either way.

[Douglas Spotted Eagle]

Find me a place to upload a 90 meg file, you can clearly, easily see the difference between the two. I'm still shocked over the BBC allegedly not seeing a difference between the two. It's clear as night and day. Anyone who attended the HDV Solutions tour saw this clearly.
It's a file that we downsampled in-camera, and downsampled in Vegas, and there is not just a small difference, it's a very large difference.

[John Poore]

I cant do a ninety meg file, but I have done Boyd's experiment and the results are that HDV looks significantly worse in terms of detail, can anyone here host a simple JPEG screen grab for me and you can judge for yourselves..?

[Sean M Lee]

DSE, I can host the file for short while...Email me at Sean at SeanLee dot tv and I can give you access.

[Boyd Ostroff]

John - it helps put your questions in perspective if we know where in the world you are; I had no way to know you were in a PAL country but suspected this might be a factor. Maybe you could take a minute to click on the Controls link above, then Edit Profile and add your location for future reference?

The test I did was brief and certainly not very scientific. I'll try to find some time later today to do another NTSC test, and maybe give it a shot in PAL mode as well.

One thing is for sure though. When playing around I switched the component output to 480p with the camera in 1080i mode. Wow, that produced an image on the monitor which was a huge improvement over DV. In fact, on my 1280x768 17" Sony 16:9 LCD monitor I could hardly tell the difference between 1080i and 480p. Unfortunately you can't send 480p over firewire, only out through the component cable.

[John Poore]

My FX1 component output only has 1080i and 576i. I take it the Z1 does 480p then?

Ps I mailed my comparison pix to Sean Lee, I hope he's ok with that. Maybe he'll put them up for us to compare.

[Steven Gotz]

There is another issue here as well. While downconverting in the NLE may look better, or may not, there is still the advantage of shooting HDV in that you can zoom in on it a lot and still retain great quality since the original frame size is so much larger to begin with. Panning around a large frame within a standard definition project has really allowed me to pull off some tricks that would have ordinarily meant that I needed to just live with a wide shot.

Picture shooting a choir from a wide angle, and then being able to pan around to get some really nice closeups after the fact.

[Anhar Miah]

John, this whole downconverting thing is what i've been hooked on for a while, and finally I think i've found A solution, AND YES there is a difference firstly the BBC report DID say there was a quality difference BUT it was only achieved when using a expensive Snell&Wilcox Ukon, and thats what got me motivated to do these tests to see if I too could achive some good downconversion.

Cutting to the chase...

If you downconvert to DV25 , don't bother DV25 is a horrible format (kiddin).

Since the final output is gonna be SD DVD, do this:

(1) Apply sharping filter to HD source + any Colour correction
(2) Render out 720*576 uncompressed (now someone said that this file will have full 4:4:4?) .avi or quicktime (I use MJPEG, its easy on my Harddrive) this quicktime OR avi will be fantastic, if viewed from a distance its almost like the original HD source!

(3) Encode your DVD from this file!

Now I dont have any files that are downconverted via camera to compare, it could be that the camera does a better job then my method.

P.S I've just had another brainwave!!, I've watched footage from my laptop via s-video to SD TV, and my screen was set to 1280*768 and I played the .m2t files at half size (to fit in my screen) (using VLC) and this image has looked stunning, absolulety stunning, COULD IT be that a simple laptop TV output has a very high quality scaler that I could record this via say a DV passthough I could potentionally get results as good as a Snell&Wilcox Ukon???

[Boyd Ostroff]

Originally Posted by John Poore

My FX1 component output only has 1080i and 576i. I take it the Z1 does 480p then?

Yes the Z1 does 1080/60i, 1080/50i, 480i, 576i, 480p and 576p. This makes me wonder if there's something different about how the different models downconvert HDV to DV as well...