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GY-HD251 framegrabs


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#1 Phil Rhodes

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Posted 31 January 2007 - 09:12 PM

Hi,

This is just the first one, but I'm doing a whole load of uncompressed recording from the new HD251 camera that'll be used at videoforum next week. Therefore, I'm interested in any questions that arise so, with any luck, I can preempt the more obvious stuff.

I apologise for the utter banality of the subject matter, it's all I could throw together this afternoon. Some people get real girls...

Posted Image

Original DPX

The camera is in a very low contrast mode here, and the blacks are pretty noisy. Seems noisier in 24P than 60. Lowest available (other than "off") amount of sharpening - "off" didn't even seem to do any aperture correction, which was too mushy for words. "Filmout" gamma, black stretch 5, white clip at 108%, 80% manual knee, matrix off, +5 colour gain, AWB reports 3000K. The (rotten) Fuji TH16x5.5 lens is at a 4/5.6 split, with about 400fc of (known greenish) fluorescent illuminating the left side of the soda can. Assuming we accept this exposure as correct, a rating of 400ASA is implied.

There are currently major problems capturing 24P with this camera on the Blackmagic Decklink hardware. Either the camera's firmware or the Decklink software contains a bug which causes the 60P/24P extraction to discard and retain the wrong frames, resulting in three successive good frames followed by two duplicate frames in the rendered video. 50/25 rates don't seem to be supported at all. I'm in conversation with both JVC and Blackmagic's technical people concerning this. 60P slow-mo is fun, in the meantime!

Not bad for a five grand camera with a five grand recorder, eh?

Phil
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#2 Troy Warr

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Posted 01 February 2007 - 01:05 AM

Wow, that does look pretty good.

So, will the HD251 record to tape at 720p60, or just through the HD-SDI output? If it does tape, how does it cram all of that extra data into the same bandwidth, without a serious loss of quality? Or does the tape run faster?
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#3 Tim Dashwood

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Posted 04 February 2007 - 11:49 PM

So, will the HD251 record to tape at 720p60, or just through the HD-SDI output? If it does tape, how does it cram all of that extra data into the same bandwidth, without a serious loss of quality? Or does the tape run faster?

Yes it records to tape at 720P60. It uses the exact same bandwidth it always has (19.2Mbps) but the GOP is 12 frames long instead of 6. There will of course be some tradeoff, but it is very difficult to see the difference when the footage is running.
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#4 Troy Warr

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Posted 07 February 2007 - 11:10 PM

Yes it records to tape at 720P60. It uses the exact same bandwidth it always has (19.2Mbps) but the GOP is 12 frames long instead of 6. There will of course be some tradeoff, but it is very difficult to see the difference when the footage is running.

Wow. That just seems like a *whole* lot of compression to me - by my calculations, that's about 6x the raw number of pixels at about 80% of the data rate of miniDV. I realize that's a gross oversimplification of compression and image encoding, but I'm very surprised that the camera can output images of appreciable quality in so little bandwidth.
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#5 Tim Dashwood

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Posted 08 February 2007 - 01:28 AM

Wow. That just seems like a *whole* lot of compression to me - by my calculations, that's about 6x the raw number of pixels at about 80% of the data rate of miniDV. I realize that's a gross oversimplification of compression and image encoding, but I'm very surprised that the camera can output images of appreciable quality in so little bandwidth.

JVC has really gone above and beyond with the design of this new "super-encoder" for 720P60.

Here's some 720P60 mpeg2 files from my PL Cine Lens Test. I was using a fairly high speed shutter because the intent was over-cranked slo-mo.

http://www.timdashwo.../.Public/dog.ts
http://www.timdashwo...ublic/craig1.ts
http://www.timdashwo...ublic/craig2.ts

Edited by Tim Dashwood, 08 February 2007 - 01:33 AM.

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#6 Phil Rhodes

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Posted 08 February 2007 - 07:32 AM

Hi,

The compressed pictures are OK.

Later, when I'm in the right place to do it, I'll post some comparison images between HDV and the uncompressed SDI captures. The HDV never looks fantastic; often, it looks absolutely terrible in comparison. It's very very compressed.

Phil
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#7 steve hyde

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Posted 09 February 2007 - 02:44 AM

...interesting results. Thanks for posting. I'd like to learn more about this system.

Steve
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#8 Rupe Whiteman

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Posted 26 February 2007 - 04:27 PM

... A bit late to this thread... Phil - what was the camera like to operate? - I've mucked about with the 100 series it supersedes and hated it's colour viewfinder and controls.... are they much better on this one?
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#9 Daniel Smith

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Posted 26 February 2007 - 04:38 PM

Sorry, random question, but why is '720' such a "standard" resolution? It seems to be the default resolution in editing software for DV as well.

I would have thought shooting either 640 (pal) or 540 (ntsc) would be better as there is no interpolation later on in post.

Edited by Daniel Ashley-Smith, 26 February 2007 - 04:43 PM.

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#10 Thomas James

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Posted 27 February 2007 - 09:47 AM

Its all a marketing gimmick by the electronic companies. True PAL widescreen is 1024x576 square pixels. But instead they only give you 720x576 oddball rectangular pixels and sell that as the widescreen format. Its the same with the 1080i format which promises 1920x1080 square pixels yet it only delivers 1440x540 rectangular pixels. And yes rectangular pixels lower picture quality but these electronic companies could care less after they get your money. The sensible solution is of course the 720p format that delivers the full 1280x720 square pixels at 60 full frames per second but then these marketing departments attack the format as not being real high definition and so they can sell you their full high definition 1080i format which offers even less resolution than 720p but has the big numbers that sell.
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#11 Phil Rhodes

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Posted 27 February 2007 - 11:31 AM

Hi,

What?

> True PAL widescreen is 1024x576 square pixels.

There has never been any such format in wide use. The system of using 1.422:1 ratio pixels was developed as a way to transport a widescreen picture using existing hardware. It's not a down-res of some theoretical higher res format - no such thing has ever existed. The only place you're likely to actually see 1024x576 frames used is if someone who doesn't know about PAR correction is working in Photoshop.

> But instead they only give you 720x576 oddball rectangular pixels

The 4:3 720x576 frame also uses rectangular pixels (more so in NTSC than PAL, but they're not square).

> Its the same with the 1080i format which promises 1920x1080 square pixels yet it only delivers 1440x540
> rectangular pixels.

No, it doesn't - that's completely the wrong idea. Some HD formats do record 1440 pixels horizontally, but that's not an inherent characteristic of whatever you're calling 1080i. Lots and lots of ways of recording full1920x1080 images exist. Also, none of them care very much whether the frame is interlaced or progressive, usually it's just a flag in the data header, so I don't know where you've got this 540 line idea from but it couldn't be more wrong. All mainstream HD formats use square pixels.

> The sensible solution is of course the 720p format that delivers the full 1280x720 square pixels at 60 full
> frames per second

Not if you want something that's easily broadcastable in a variety of places. The only place you can easily show 60p material is on a 720/60p HD network. Otherwise, you're left to reduce it to 30i NTSC or do a quality-sapping standards conversion to PAL. I'd hesitate to shoot any 60p format unless it was for a very, very specific reason. As for shooting 720 - well, it's clearly a no-brainer that 1080 outresolves it, but that seems to be the point you're arguing, and I don't quite get what you're trying to prove here.

> 1080i format which offers even less resolution than 720p

Well... I mean... can you count?

Now, you can state an aesthetic preference about interlaced scan images, and I'd probably agree with you, but any 1080 format is going to exceed any 720 format in terms of raw resolution, even taking into account anti-flicker processing. I'm trying to interpret what you're trying to say here and I suspect that it's coming from some kind of dislike of the interlaced-scan Canon HDV cameras or something, and it's true that in tests I've run, the deinterlaced Canon images have more or less the same resolution as the progressive scan JVC images. I'd prefer the JVC, but not because of anything to do with resolution or frame rate.

What point are you trying to make?

Phil

Hi,

> Sorry, random question, but why is '720' such a "standard" resolution?

I believe it's coincidence that the height of one type of HD and the width of SD is the same number.

720p HD is 720 pixels high because it's 1280px across and it needs to be a 16:9 frame. Why is it 1280 pixels across? Well, that's because... eh... erm...

> I would have thought shooting either 640 (pal) or 540 (ntsc) would be better as there is no interpolation later on
> in post.

You're confusing width and height. PAL Frames are 720 pixels wide by 576 high; NTSC frames are 720 by 480 (or 486 sometimes).

Was that the questin you were asking?

Phil

Hi,

> what was the camera like to operate?

Fine - like a small ENG camera.

> I've mucked about with the 100 series it supersedes and hated it's colour viewfinder and controls.... are they
> much better on this one?

I suspect the viewfinder is exactly the same. Yes, it's feeble, but to be honest I am not aware of a really seriously good solution to the HD viewfinding problem that doesn't have one or more problems - strobing, monochromacity, lack of resolution, etc. The best stuff is on the Sony HDCAM series, but then I'm used to black and white viewfinding. At least you can see focus, though. Focus really is eyebrow-raisingly critical, even on these little 1/3" chip cameras.

Controls are more or less as you'd expect on any ENG camera, just on a smaller frame. It's got all the standard toggle switches; assignable buttons; it's got a sensible amount of DSP controls in the menus, and you can turn the LCD into a large-digit status and timecode display.

I really like the GY-HD series stuff. Does need a better viewfinder, though, to be honest.

You can read my Showreel article about the HD251 here.

Phil
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#12 Brian Drysdale

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Posted 27 February 2007 - 12:19 PM

Regarding your glassware concerns, the new HZ-CA13U 16mm PL mount adapter looks like interesting addition to the range, especally for drama work. Tim Dashwood over on DVInfo has been doing some tests and the results look extremely good.
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#13 Phil Rhodes

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Posted 27 February 2007 - 06:24 PM

Hi,

Here's some stills from the material I shot for Videoforum demonstrating the difference between the HDV and SDI recordings. Excuse the enormous BMPs - it was the easiest way to do it.

Demo 1
Demo 2
Demo 3
Demo 4

The subject is the rotating reel on a 1/4" tape deck, occasionally with other rotating spoked reels in front. I think it's fairly obvious from this that the camera is being absolutely murdered by the codec. That said, this is the least favourable codec situation, since it was recorded at 60p, and I designed the test to produce maximum stress.

Still, worth recording uncompressed if you possibly can. If you want to make the HDV look incredibly bad, just crank the contrast up a bit in your favourite imaging application - grading HDV is clearly a minefield.

Phil
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#14 Alex Lindblom

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Posted 19 March 2007 - 12:06 PM

Hi Phil.

I am just curios do you know or do you want to speculate if it would be possible to hook this camera into an SRW1.

I mean the connections are there SDI and Sony states it can record "In standard configuration, the SRW-1 can record in 4:2:2 720/59.94P format".

It seems plausible but maybe I am missing something.

Alex
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