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Canon XL and GL Series DV Camcorders
Canon XL2 / XL1S / XL1 and GL2 / XM2 / GL1 / XM1.


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Old December 15th, 2004, 05:02 PM   #31
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Yeah, everything gets fuzzy. And calling it 960x480 confuses issues too, because by the time it hits tape it's 720x480. And then they wonder where that went, and isn't the FX1 better because it's 960x1080 and... on and on...

For "full resolution" I was referring to shooting a resolution chart. If the camera will spit out a resolution chart that shows 540 lines of resolution, then that's what I was calling "full resolution" -- which is the limit of DV's recording capability. But, as you point out, that's not the be-all-end-all definition, either...
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Old December 16th, 2004, 03:40 AM   #32
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Why can't we just define it like:

" if the field-of-view widens when you switch from 4:3 to 16:9
mode your camera (or anamorphic attachment) does true 16:9
and you get an increase in resolution. Otherwise it is a fake 16:9 "

That should be precise and easy to explain.... no?
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Old December 16th, 2004, 12:17 PM   #33
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Seems reasonable, but...

... I don't know, it just seems to legitimize the compromise Canon made for 4:3 mode. I mean, why doesn't the XL2 use its full 4:3 CCD when in 4:3 mode? Primarily it would appear that they did it for marketing purposes: to make you think you're getting "more" when you go to 16:9 mode, as opposed to what's actually happening, which is that you're getting "less" when you go to 4:3 mode.

Look at it this way: what if Canon did everything with the chip exactly as they did, but instead of using a 1/4" subset of the 16:9 patch, they let you use the full surface of the chip for 4:3 mode. By that token, you'd get the same "true" 16:9 you already have, which would fulfill my definition of "full resolution", and you'd have a much larger chip surface area for 4:3 (ostensibly better than what we have now, right?

But by your definition, it would fail the test of "true" 16:9, because the FOV wouldn't get wider in 16:9 mode.
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Old December 16th, 2004, 02:14 PM   #34
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<<<-- Originally posted by Barry Green :
Look at it this way: what if Canon did everything with the chip exactly as they did, but instead of using a 1/4" subset of the 16:9 patch, they let you use the full surface of the chip for 4:3 mode. By that token, you'd get the same "true" 16:9 you already have, which would fulfill my definition of "full resolution", and you'd have a much larger chip surface area for 4:3 (ostensibly better than what we have now, right?

-->>>

Then you would have a situation where the 4x3 image would have more pixels to sample from making it "higher res" than the 16x9 mode. In which case everyone would be up in arms again because 16x9 would be compromised. This would lead to a desire for an anamorphic adapter so that 16x9 freaks can take full advantage of all the pixels in 4x3 mode. It is a catch 22. At least the way it is now, Canon has clearly marketed the camera to succeed in 16x9 mode and be competetive in 4x3.
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Old December 16th, 2004, 02:39 PM   #35
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There are some technical reasons why the full CCD height readout would not be applied in 4:3. The first is optics related: a larger chip diagonal could lower the image quality in the corner area's (vignetting, aberations..). A second one would be the need for a different line readout algorithm (polyphase filter)for 4:3. A third reason could be that part of the CCD is optically screened off and used as a buffer memory in progressive mode (semi FT mode)
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Old December 16th, 2004, 03:26 PM   #36
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The active region in 4:3 is 720 x 480 - exactly the number of samples in each direction required for transfer to tape. Thus no interpolation is required. If the full sensor were (could) be used then subsampling would be required in which the extra resolution would be thrown away anyway (Note: in horizontal up by 3 and down by 4 and in vertical up by 2 and down by 3 gives 729 x 480 so polyphases wouldn't be necessary). What might be nice would be to do the antialiasing filter digitally and even perhaps to give the user some control over its cutoff so that he could eliminate jaggies (to some extent, at least) where they are annoying and go for full resolution where they aren't.

Agree with Andre that there might be lens coverage problems at the corners and also that those inactive areas are probably not available.
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Old December 16th, 2004, 05:04 PM   #37
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There can't be lens coverage issues -- the chip is exactly the same size as the XL1's, and the camera uses XL1 lenses and the XL1 can use XL2 lenses.

So in theory on a different camera that might apply, but for this camera it should be a complete non-issue.
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Old December 16th, 2004, 07:21 PM   #38
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True if the XL1s used the whole chip (i.e. no fallow pixels as on the XL2 set). Probably true for all practical purposes even if it didn't. The remark was really based on the observation that use of the whole chip for 4:3 on the XL2 would take you 12% further from the lens axis than the 16:9 mode.
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Old December 16th, 2004, 10:13 PM   #39
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Well, while all you silly persons are arguing semantics, I think I'll go shoot some video. ;-)~

Happy Holidays, everyone. Catch the spirit!
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Old December 21st, 2004, 05:49 AM   #40
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As said earlier, if they would do a full 4:3 readout we would be
back at the XL1(S) camera where we do not have a full 16:9
mode but a faux one. That is the whole idea. If you have a true
16:9 camera 4:3 mode WILL ALWAYS be lower resolution.

Heck, this is even true with an anamorphic attachment and a plain
4:3 camera. With 16:9 attachment on you get true 16:9 and an
increased resolution. Withouth it you are at plain 4:3 and you have
lost the increased resolution. This is always true!

So you have the following choices:

1. fake 16:9
- no resolution or FoV increase
- no resolution change between 4:3 & 16:9

2. true 16:9 (whatever method)
- resolution and FoV increase in 16:9 compared to 4:3
- 4:3 is lower resolution than 16:9 (that is the whole idea)

But as I've said time and time again on this board: I personally
don't care about resolution. The chance of my footage coming out
on some medium where people (on usually crappy equipment)
will actually see the difference is SMALL.

Yes we wan't the best quality we can get, but why not focus all
of this energy at making some good stories and movies?

Resolution is only a small factor in the succes of a movie, I can
garantuee you that!
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Old December 21st, 2004, 08:17 PM   #41
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<<<-- Originally posted by Rob Lohman :
2. true 16:9 (whatever method)
- resolution and FoV increase in 16:9 compared to 4:3
- 4:3 is lower resolution than 16:9 (that is the whole idea)
-->>>

Rob, if DV is 720x576 (or 720x480), whether it is 4:3 or 16:9, why do you say there is an increase in resolution in 16:9 compared with 4:3? I would agree there is an increase in resolution if you compare native 16:9 to stretched 16:9, but not that one set of 720x576 samples is higher resolution than another. Am I missing something?

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Old December 21st, 2004, 10:34 PM   #42
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<<<-- Originally posted by Richard Hunter : <<<-- Originally posted by Rob Lohman :
2. true 16:9 (whatever method)
- resolution and FoV increase in 16:9 compared to 4:3
- 4:3 is lower resolution than 16:9 (that is the whole idea)
-->>>

Rob, if DV is 720x576 (or 720x480), whether it is 4:3 or 16:9, why do you say there is an increase in resolution in 16:9 compared with 4:3? I would agree there is an increase in resolution if you compare native 16:9 to stretched 16:9, but not that one set of 720x576 samples is higher resolution than another. Am I missing something?

Richard Hunter -->>>

The concept is that the more pixels that are sampled from the CCD the higher the perceived resolution is, regardless of the actual "DV" pixel count. To give an over simplified example I take a high res photo taken from a 35mm still camera and drop it into a DV piece I am editing on my PC. When I cut from the actual DV camera footage to the 35mm shot there is a huge difference in the resolution and clarity of this shot. IT is obviously a much higher qulaity source image. This proves that regardless of the DV compression, it is possible to see more information if the source material is more detailed.

Therefore a 940x480 16x9 source image from the CCD on the XL2 has the potential to look more clear and precise than an image acquired from a 720x480 sample from a source CCD on other prosumer level cameras, regardless of the compression after that stage.

Make sense?
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Old December 21st, 2004, 10:37 PM   #43
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Hmm. Well said there, Marty!
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Old December 22nd, 2004, 04:19 AM   #44
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Hi Marty, thanks for the explanation. OK, there are probably other good reasons why the image from 35mm film is clearer than those from a DV camera, but I get what you are saying. Even so, the 940x480 resolution would apply only for a system such as used in the XL2 and not to native 16:9 per se, right? For example, if the CCD is 16:9 aspect ratio and has 720x480 pixels, it would still be native 16:9 but I don't see that it would have higher resolution than 4:3 at 720x480.

Richard
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Old December 22nd, 2004, 04:49 AM   #45
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Besides the excellent point made by Marty you also have an
actual increase in resolution: the vertical resolution. Let me
clarify by a short example:

Normal NTSC DV is 720 x 480 pixels.

A fake 16:9 camera that does an anamorphic stretch does the
following:

1. crop the signal to 720 x 364

2. stretch that back out to 720 x 480 (upsampling)

(or it can do the stretch first and then a crop, but that's the exact
same thing)

So you are now working with a 720 x 364 pixel image instead of
720 x 480! Which looses you 116 lines of resolution (which would
be the same if you letterboxed it for example)!

A true 16:9 camera like the Canon samples the image in 16:9
mode at 960 x 480: http://www.dvinfo.net/canonxl2/articles/article06.php

So the only thing this camera has to do is:

1. stretch the signal back to 720 x 480 (downsampling)

In this case you "loose" resolution in the HORIZONTAL (since you
go from 960 to 720 pixels per line). However, the VERTICAL can
stay the exact same.

If you compare this to the faux method you see that you gain the
116 lines of resolution that you lost there.

So you have two things to gain from a true 16:9 camera or a
camera with an anamorphic attachment that records in DV:

1. an increase in VERTICAL resolution

2. a higher sampling resolution which yields a richer image (Marty's point)

This is the exact same thing that happens with a DVD (the image
recorded there is 720 x 480 as well, anamorphic 16:9 or not!).
The increase is in vertical resolution and not horizontal or both.

Ofcourse the best thing would be to not re-sample/scale/stretch
the image at all and get the full 960 x 480 image, but that is just
not allowed in the DV standard (for bandwidth reasons at that
time etc.), so that's not going to happen.

The only thing one can do is go to a HD format for even greater
resolution, but even those sometimes have stretching.

For example, the new Sony camera records at 1440 x 1080 instead
of the full HD 1920 x 1080 signal. What they have done is that
they are recording at a different pixel aspect ratio so that 1440
must be horizontall stretched (upsampled) to 1920 which ofcourse
looses you some resolution. Although it is still (much) more than
960 x 480 in plain SD resolution.


Richard: to answer your question: with such an attachment the
chips will not change and you can argue about resolution. In this
case you will still benefit from my point #1 in the list above (since
you get to keep the full vertical resolution) and point #2 is the one
you can argue about. In my opinion you gain in optical resolution
instead of true pixels like a true 16:9 CCD.

The end result should however be the same with a good enough
piece of anamorphic glass in front of your camera!


I hope this post has clarified some things!
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