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Sony HVR-V1 / HDR-FX7
Pro and consumer versions of this Sony 3-CMOS HDV camcorder.


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Old November 6th, 2007, 01:57 AM   #16
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Originally Posted by Graham Hickling View Post
That can be caused by using too high a shutter speed, so that the blur in the two individual fields doesn't blend well when the fields are combined into a 30p frame.
Shutter speed? If the fields are being blended into one another then the problem lies at the encoding stage. A low shutter speed could hide the problem somewhat, but it will be still there. Blended fields look horrible.
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Old November 6th, 2007, 09:11 AM   #17
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Converting 60i to 30p combines the information from two fields into one frame.

Even using a motion-compensated deinterlace or whatever, if the field images are taken at shutterspeeds higher than 1/60 the result is a spatial gap between the end of the motion blur in the first field and the start of the motion blur in the second field, so that when the fields are are combined the result looks bad.

There are dozens of posts around saying "don't use auto shutter if you plan to deinterlace", and the result if you do in bright light is similar to what the OP described.

Just my $0.02. It's easy enough to try a short test clip ...
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Old November 6th, 2007, 10:34 AM   #18
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Originally Posted by Graham Hickling View Post
...There are dozens of posts around saying "don't use auto shutter if you plan to deinterlace"...
Um... don't use auto shutter if you plan to have your video shown anywhere outside your home!

Auto-shutter and auto-gain will do more to unpredictably screw up your video than just about anything. If your subject and shooting environment would benefit, or, if you're looking for a particular effect, you should be making the decisions about what shutter speed or level of video gain to use, don't ever leave it to the camera electronics. IMNSOHO, YMMV!
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Old November 6th, 2007, 06:59 PM   #19
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Originally Posted by Seth Bloombaum View Post
Auto-shutter and auto-gain will do more to unpredictably screw up your video than just about anything
Before you steer folks wrong -- these two are very different.

Auto-shutter gives your camera permission to push shutter-speed much higher than 1/60th or even 1/100th. This can cause the visual problems -- strobbing -- folks are talking about. So yes, you want to turn it off. And, in most cases you set the shutter-speed based on frame-rate and that's the end of it.

Auto-gain enables the camera to increase gain UP TO THE LIMIT YOU SET. If there isn't enough light to produce a good pix at 0dB gain -- then increasing gain is exectly the correct thing to do. It's exactly what a human operator would do. The difference between man and machine is that a human would watch the image and decide when the pix got too much noise. The fact is that in most cases that occurs when gain goes over +12dB.

Some JVC cameras solve this problem by simply limiting gain to +12dB. In this way, they can use AGC ON/OFF. (To limit gain to about +9dB use Twilight.)

Sony, of course, allows the camera to go to +18dB gain. But, if you know how to use the V1, you can set your own limit.

Ranting about the virtues of manual control are about a decade too late. Today, computers can control -- assuming YOU set the limits and choose when to allow the computer to function -- faster than humans. In the still photo world -- no one today would try to beat AF. It takes a human a half-second to respond to a visual change. An AF lens has done its job by the time you have registered that something needs to be done.
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Old November 6th, 2007, 10:35 PM   #20
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Originally Posted by Graham Hickling View Post
Converting 60i to 30p combines the information from two fields into one frame.
So... I theoretically should not be losing resolution when I convert my Z1 60i footage to 30p? Or... convert 50i footage to 25p?

Whenever I use HDLink or Premiere to deinterlace, it drops my resolution to 1440x540, icky. Can I fix this and greatly improve my workflow?

C
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Old November 7th, 2007, 01:44 AM   #21
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...Ranting about the virtues of manual control are about a decade too late. Today, computers can control -- assuming YOU set the limits and choose when to allow the computer to function -- faster than humans...
Well, it's true, I am a fossil.

Although Steve's description of what autogain is, and how you can limit it's operation to a preset on the V1 is accurate... and objectionable noise grain doesn't show up till past 9db on the V1...

I wanna' decide. You don't have to be raised with the dinosaurs to want to control the image. Deliberate design of the image is what pro camera work is all about. This (usually) means working under controlled conditions where my flakey brain is plenty fast enough to account for changing light, if any.

If the gain or iris is in automatic you're not just yielding exposure control to the camera, you're yielding depth-of-focus control as well.

I'll not hesitate to use auto-iris and/or auto-gain if a shot calls for making a sudden transition between interior and exterior lighting - but that's very rare for me. Reality TV camera ops will have different standard procedures, they gotta' follow the action and do it now, but I'm working in a more planned fashion.

Too often, "the camera does such a good job" is an excuse for ignorance of the basics of the numerous camera controls that affect exposure. This can quickly lead to questions like "Why is my subject silouetted? Why does this person of color look like a caucasian? Why is there no detail in the highlights on this person's face? Why can't I see this person's eyes, they're in deep shadow?"

Turn one exposure-related function on automatic and you lose control of all those issues. Granted, the camera's automatic settings can react quickly to changing lighting. But the camera does not know what is important in the scene, and can't distinguish between a face, a basketball and a desk lamp.
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Old November 7th, 2007, 03:10 AM   #22
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Originally Posted by Steve Mullen View Post
Auto-shutter gives your camera permission to push shutter-speed much higher than 1/60th or even 1/100th. This can cause the visual problems -- strobbing -- folks are talking about. So yes, you want to turn it off. And, in most cases you set the shutter-speed based on frame-rate and that's the end of it.
I've seen that most pros / experienced people recommend this and I really, really want to trust this as I acknowledge the greater experience.

I wonder though:
- From a perceived quality point of view, I found that motion blur in HDV makes a significantly higher impact on the viewer's experience (vs. SD DV), just like focus blur does (remember focus is critical in HD?)
- For slight / slow pans of scenic buildings or viewpoints, I found that 1/100 shutter speed is nicer than 1/50 (I shoot 50i) as it better preserves details when panning.
- When shooting in motion (car or train), shooting 1/50 just leaves me with a mish-mash of motion blur that really isn't nice to look at (barely usable). Therefore I'd rather intend to increase to 1/150, maybe 1/200. I don't expect CBR MPEG2 to encounter a bandwidth limitation with increased detail, do I?

My question, then:
- Is it just a matter of subjective preference? Is it a collective 'yuk!' in the professional community that requires 'serious filming' to stick to 1/50 (or 1/60), so I'd rather go to higher shutter speeds just because I'm a consumer with different tastes?
- Or is there some real technical hard wall that I'll be hitting someday, that I'm not yet aware of? Note that I've already gone through the whole workflow to viewing edited footage on a Full HD display (1080i all-scan) with camcorder hooked through HDMI connection - a decent set-up for proof-checking.
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Old November 7th, 2007, 03:26 AM   #23
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Stephan,

While it's true "real pros" stick to 1/50th (PAL) or 1/60th (NSTC) to maintain compatibility with their producers' (TV stations?) requirements, I have long ago tested and approved a much more relaxed range for usable shutter speeds with my V1E. When in low-light, I shoot at 1/25th (in 25p mode this is eauivalent to "shutter off", and gives me a one full stop of more exposure). In bright sunlight, depending on the subject I sometimes go as high as 1/150th, for the very reasons you mention.

I have found that the 2 most often mentioned disavdantages of such a fast shutter: strobing and rolling shutter effects, are not noticeable in my pictures at all even with 1/150th, while the blurring is almost totally eliminated. Additional bonus being I can keep the iris open and get a controllable, shallower DOF - even on a summer day at noon, and on the beach :)
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Old November 7th, 2007, 04:57 PM   #24
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Okay thanks. Unless anyone here comes up with hard facts about that technical hard wall that the two of us don't see, I'll take this as an issue of corporate standards that pros have to comply with. Makes sense.
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Old November 9th, 2007, 11:29 AM   #25
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Originally Posted by Carl Middleton View Post
So... I theoretically should not be losing resolution when I convert my Z1 60i footage to 30p? Or... convert 50i footage to 25p?

Whenever I use HDLink or Premiere to deinterlace, it drops my resolution to 1440x540, icky. Can I fix this and greatly improve my workflow?

C
Unfortunately the fields can't simply be added to each other losslessly, as that would produce 'comb' artifacts whereever there is motion. There are however various 'motion-compensated deinterlace' software plugins around (e.g. for Virtualdub) that retain as much information as possible so in up with a resolution intermediate between fully interlaced versus a 'dumb' deinterlace that simply blends the fields together.
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Old November 9th, 2007, 12:33 PM   #26
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Originally Posted by Graham Hickling View Post
Unfortunately the fields can't simply be added to each other losslessly, as that would produce 'comb' artifacts whereever there is motion. There are however various 'motion-compensated deinterlace' software plugins around (e.g. for Virtualdub) that retain as much information as possible so in up with a resolution intermediate between fully interlaced versus a 'dumb' deinterlace that simply blends the fields together.
Gotcha!

I did some tests with 50i->25p->23.97p using Cineform when I convert from m2t to Cineform.... it actually looks really good! I set the frame type to Progressive instead of auto and the 25p->23.97p rate change.. deinterlace set to off. I see combing artifacts as described only while playing in Premiere, I stopped and looked at frames from the output and there was no combing only some rather realistic motion blur... was really impressed! Thanks for the tech breakdown on what I've been testing, I hate not knowing what negative effects that might have, and appreciate you filling me in!

Carl
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Old November 12th, 2007, 12:35 PM   #27
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That's what I've been doing, though I shoot in 50i and CineFrame 25 on the Z1u. I also use either ProRes 422 or Photo-Jpeg at 75% quality (that gives you 4:2:2 Y/Cb/Cr footage, not less video quality; 100% will give you RGB--thanks to RED's Graeme Nattress for the tip).

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