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Old May 16th, 2004, 06:06 PM   #646
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I wonder if this problem is also evident in the DV frame i posted? i.e. how does the camera originally deal with it? I'm thinking they just got it as close as possible...
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Old May 16th, 2004, 07:54 PM   #647
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DV footage

I just took a look at it... from what I see, there's no difference between any of the three channels in the DV frame. The camera has to be doing something to compensate what's happening in the green channel. I'm gonna keep studying the raw version and the DV version to see if there are more clues as to what's happening.

John
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Old May 16th, 2004, 09:32 PM   #648
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Strange

When I place the DV still on a layer above the Raw version, they don't match up at all. The DV version is narrower on its horizontal axis than the raw version. I had to enlarge it by about 106% horizontally for the balcony posts to line up on the two.

Why is that? Could it be a clue? And what does that mean the correct pixel aspect for the RAW footage you're pulling off the chips is? I guess I assumed that it was the same as DVs .9

Am I missing something?

John
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Old May 16th, 2004, 09:53 PM   #649
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Green flourescent posterboard is actually a near-perfect color for greenscreen.

Juan, you shouldn't have to uprez to correct the problem -- you should be able to just use interpolation to do a sub-pixel distort or scale or whatever.

I'll dig up those interpolation functions and send them over with my notes!

- ben
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Old May 16th, 2004, 10:08 PM   #650
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DV vs RAW

When I say narrower on the horizontal axis what I mean is it's more compressed horizontally than the RAW version.

John
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Old May 16th, 2004, 10:08 PM   #651
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John,

The chips in the DVX are NTSC so the image will look wide unless you apply the correct NTSC 0.9 pixel aspect ratio.

Also, I know for a fact that there are some columns and maybe horizontal lines which are cropped off by the camera for the DV footage, and what's left is resized.

However, now that i think about it, even if the only difference in the green channel is some optical FOV, we should still be able to match the pixels by doing a transformation...afaik it should be close to linear. We can take samples at extreme points in the image and then adjust, shouldn't be that much more different than a resize if it is linear.
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Old May 16th, 2004, 10:40 PM   #652
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Juan, you can also buy some green paint at Lowes, I used that to paint our cyc wall and it works very well..make sure it's the most pure green they have..
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Old May 17th, 2004, 02:01 AM   #653
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0.9 pixel aspect

Juan,

I don't think you understand what I mean. The DV clip is 720 x 480 right?... which will appear a bit wider unless you apply the 0.9 pixel aspect ratio to it. That will reshape it to something proportionate to 640 x 480 square pixel... and thus it will look normal on a monitor... But what I'm seeing is a difference between the the DV frame you uploaded (720 x 480... which has not had the 0.9 applied and is therefore a bit wider than normal, agreed) and the RAW frame (773 x 495... which has not had the 0.9 applied either AND YET is even more "stretched" wide than the DV frame.) Why wider than the DV frame?... the DV frame is stretched wide enough... applying the 0.9 pixel aspect to DV 720x480 will correct it to the normal propotion, but if the RAW frame is even more "stretched" then it needs an even lower pixel aspect than 0.9 to correct itself. Am I crazy... does anyone else understand what I'm seeing?

John
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Old May 17th, 2004, 08:09 AM   #654
 
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Does anybody know about this new Final Cut Pro HD? It claims 10 bit 4:2:2 uncompressed 1080p at 90-160 MBps via PCI transport . . . and from SOFTWARE alone (No additional hardware)?

I'm not sure I buy this. I will say that if it does what it claims, it would limit the 4:4:4 idea, but sure gives us enough for Hollywood level acquisition.

Somebody tell me what I'm missing here:

http://www.apple.com/finalcutpro
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Old May 17th, 2004, 11:04 AM   #655
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Don't spend a lot of time trying to light the blue/green screen setup. Just point one light at it and the subject. I know it will give harsh shadows on one side but that isn't important right now. We just need to test the side the has no shadows. Besides it would be nice to test how well the mod performs with a very bad keying setup. I assume even with bad lighting a 4:4:4 signal would be much easier to key than a DV signal would. If it was a perfect screen with perfect lighting we might not be able to tell as easily how much better the mod is. Clearly it would be better but we would get the full effect by having a badly lit setup.

If you can't get to the store you could always print out a piece of paper full of a solid 255 green image. This of course would be a huge waste of ink.
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Old May 17th, 2004, 01:38 PM   #656
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John,

Ok, here's what i see. I do understand what you are saying but I am not experiencing the same problem.

The RAW frame DOES cover a wider field than what is on the DV footage. The camera crops that off but we can see that area in the RAW footage, so right away the image is dimensionally wider. However, as for 'stretching', as long as I apply the 0.9 pixel aspect ratio on the RAW footage, it looks fine. I can especially see it on some shots of resolution charts, you can judge by the circles. The circles are ellipses without the pixel aspect ratio correction, and become circles with it applied.

What has everyone else noticed?
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Old May 17th, 2004, 02:10 PM   #657
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John,

I think i found what you are talking about..in the DVComp2, the DV version covers a slightly wider field of view, and i just noticed this...however i'm pretty sure that the camera must've been moved when i pressed the record button, it's a pretty shaky setup.

I'm going to try and take another set without movement.
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Old May 17th, 2004, 09:43 PM   #658
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DV vs Raw

Juan, is part of the 773 x 495 image being cropped or masked by the camera in order to fit the 720 x 480 DV dimensions? or is the whole thing being resized? If it's being cropped as I had assumed from previous postings, then while yes it does seem that there's a different field of view in the DV (like you accidentally moved the camera), I wouldn't say the FOV is SLIGHTLY wider. In the DV you see almost an entire plank of wood more than in the raw version. If there was even more area of the DV image that was cropped than that extra plank then that setup must have been shaky indeed... you would have had to really knock the camera in order to change the FOV that much. Anyway, those two clips are too different to compare and analyze correctly. If you could capture another two that would be great. This time hit the record button first and then start the capture. And if you can, it would be great if you could take it off letterbox mode... that would help the comparison process... I want to figure out what's going on in that Green Channel and why the DV footage doesn't seem to have it.

Thanks,
John
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Old May 17th, 2004, 09:48 PM   #659
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Will do...you're right, the only way is if i hit the zoom by mistake a bit...but we all know how touchy the zoom is when it is set to manual.

I will take another outdoor set tomorrow, and hookup the joystick so I can set the letterbox off.
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Old May 17th, 2004, 10:19 PM   #660
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Juan, I figured something out

I went back and took a look at that test chart you posted a couple weeks ago... very interesting.

First I scaled the image horizonally to match a 0.90 pixel aspect. And yes the circles appeared more like circles... but then I compared them to a perfect circle I created using the elipse tool while holding down shift. The circles are not perfectly round, they're a bit wider than the perfect circle I made. Of course if you've been looking at the wider version for a while then the 0.9 version certainly looks more natural, but it's still not totally propotionate.

Then I just tried resizing the 773 x 495 image to 640 x 480 (which is the size that a 720 x 480 w/pixel aspect 9.0 applied scales to.) and the circles were perrrrrrrrrfect. There's no doubt that you knocked the camera on the last comparison shots, but there's also no doubt in my mind that the raw image is more stretched out than the DV images. It actually appears that what's happening is that the camera is simply reshaping the 773 x 495 image to 720 x 480 before or durring the DV compression. So there is actually no extra part of the image we're seeing... we're just getting a higher resolution image... which is still fantastic.

Thoughts? Am I missing something? Getting somehting wrong?... I'm no expert, but this is what I'm seeing.

John
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