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Old April 1st, 2004, 05:58 AM   #271
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<<<-- Originally posted by Juan P. Pertierra : Right now the bits not being captured are the low-order bits, so the scales should be spread evenly, just loose precision. Apparently, doing an auto-levels(spread the values so they cover the entire range) does the trick as shown on the second image.

Juan -->>>

Just watch out that whatever image transformations you do on the RAW data that you're not inducing the potential for banding artifacts. If you run a levels filter on the image when the camera is recording and writing to disk, and then we run another levels filter when we try to color correct our images, that might be enough to start some banding artifacts, which IMHO defeats the whole purpose of getting RAW data at 16-bits.
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Old April 1st, 2004, 10:05 AM   #272
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Peter, your s-vhs or y/c out is before the compression hits the video..so its 4:2:2...that is why you get a better key off y/c out..I used it for a spot I did that I needed a really good greenscreen key
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Old April 1st, 2004, 11:33 AM   #273
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Ok, i have found the source of my confusion...i am using photoshop 6 and whenever I change mode to 16-bits/channel, it won't let me do layering. This is why the files where 8-bit, not because of limitations of the TIFF format.

Is this a limitation of PS6 only? I'm going to try and do it in Shake....
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Old April 1st, 2004, 11:39 AM   #274
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Jason, bitshifting or multiplying the data isn't going to introduce any banding, because you maintain the number of color levels. You go from 4096 to at least 32768, so you're not losing any of that information. When Juan talks about a Levels call, he just means bringing in the In White Point, which is equivilent to multiplying the data.

Also, 4096 values (68.7 BILLION possible colors) gives you a TON of leeway in terms of banding. You'd have to be applying a very extreme levels call to be able to make it band. Keep in mind that 10 bit Cineon only has 1024 values (1 billion colors), and only a fraction of those values are used on the "normal" image range.

Also, any levels call would probably happen in 16bit space, not 12 bit space, which means a value that was 16000 before the levels call could wind up as 15999 or 16001. 16bit space has no fewer than 35 TRILLION colors for you to play with. So those initial 4096 values will be preserved as much as possible.

Basically, data loss resulting from upping the bitdepth is not something to be concerned with...

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Old April 1st, 2004, 11:46 AM   #275
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Juan:

In Photoshop CS, I can do all layer operations with 16-bit TIFFs. I think 7 does as well, but not sure. Many filters and plugins don't support 16-bit operations, but standard PS adjustments (levels, contrast etc.) work fine.
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Old April 1st, 2004, 12:47 PM   #276
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I'm trying to provide as many updates as I can, so here's another one. I have uploaded a complete frame so you have an idea of what frame size i'm getting out of it...important to note is that the CCD has 0.9 NTSC aspect ratio pixels, so in order to see the correct image you would need to use a viewer that can compensate for this.

This image, however, is an extremely bad one not only because of the noise you all know about, but because somewhere along the line I am getting a serious problem with two of my channels...some areas that come out black in the raw file are coming out shifted to a different level, and it has to be a problem with my code, cause the capture is fine.

This is 9-bits/channel at the most, probably very innacturate in the green and blue. Also, i had trouble getting an exact match of the blue layer position-wise, because it comes out inverted from the prism and it's very hard to see and move exactly to match.

http://expert.cc.purdue.edu/~pertierr/ScottsBook.tif

I hope i am not doing something illegal by posting the book cover...it just makes a good test image. :)

Oh and the yellow blotch on the paper is not a highlighter spill, it's actually one of the bits i mentioned before, just went to zero in that whole area....same situation with the noise in the rest of the image....i know where the problem is, i just want to test as much as possible before i start breaking it apart again.
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Old April 1st, 2004, 12:50 PM   #277
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Juan:

I edited your post to make the URL easier to download using the tags...
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Old April 1st, 2004, 01:22 PM   #278
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Thanks Stephen!

About the clips: I am getting continous frames(say what about slow hard disks? :) ), but since the camera is sitting on my test bench there's no motion going on, so there's no point in putting together a clip.

I'm going to try and move it to the window and record something moving this afternoon or tomorrow morning.

Juan
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Old April 3rd, 2004, 04:50 AM   #279
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Y/C Out

Obin... you're saying that if you record the signal coming out through the s-video connection using a video card that supports uncompressed video direct to disk, that the video isn't gonna be 4:1:1 re sampled to 4:2:2 but just clean 4:2:2? If that's the case then Juan's prospect of pulling 4:4:4 video off the chips is really the only exciting feature of this work, right? Don't get me wrong, it's EXTREMELY exciting, but this thread started out by saying that this process could most practically be used to turn the DVX100 into a camera with the kind of recording power as the 900. If you can already record the signal as 4:2:2 before it's gone through the DV downgrading process then wouldn't that be the same recording power as the 900? Excuse me if I sound naive... I may be missing something.

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Old April 3rd, 2004, 09:39 AM   #280
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I've never agreed with the practice of capturing through Svideo to get a better image. First of all, Svideo is much lower resolution than MiniDV, so you lose a ton of your image right there. Secondly, the image may technically be "4:2:2", but if you look at the chroma channels, they are actually very blurry, and *less* detailed than the MiniDV footage. Furthermore, you have the classic problem of analog video, chroma drift. This is where the chroma is smeared off to one side, so that it's not quite aligned with the Luma.

The blurry chroma channels are why people think this method is better for chroma key -- but really, you can get a far superior key (and image) by capturing normally to MiniDV and blurring your chroma channels moderately before keying. The advantage here is that you have control over how much blurring is going on, and you don't have to worry about Luma/Chroma alignment.

Of course, maybe I'm biased because I wrote a plugin called dvmatte, specifically designed for keying with DV footage... ( http://www.dvgarage.com ) It handles all the chroma blurring internally, and includes special techniques for re-introducing detail into the key...

I challenge anyone to post a "4:2:2" frame of a blue/greenscreen shot next to a MiniDV frame of the same shot. It should be clear to the naked eye which is the superior image...

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Old April 3rd, 2004, 09:50 AM   #281
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Ben I love your plugin! but in the end after all is said and done I got a much better key from y/c capture direct to disk then I ever could from your plugin....and I really really tried to make yours work...for many shots your plugin is great but some the y/c capture just worked better...you don't have to challenge anyone, I KNOW dv is "better" but sometimes it's keys are not...
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Old April 3rd, 2004, 09:56 AM   #282
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Ben, y/c out has no chroma blockies like dv does..that is the ONLY reason I could pull a better matte...i'ts not that y/c suppresses them,,they just dont exist period...i talked with Panasonic and they also told me that y/c does NOT hit dv compression on the way out... Peter y/c sucks Juan's 4:4:4 digital out is MUCH MUCH better then Y/c.....
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Old April 3rd, 2004, 09:59 AM   #283
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Since all the Svideo capture is doing is massively smearing the chroma, one thing to try when dvmatte is not working out is increasing the chroma blur. You should never see the "blockiness" of MiniDV chroma after dvmatte is done with it. Besides blurrier chroma channels, there are really no other reasons why keying Svideo would work better than MiniDV.

Especially if you're using dvmatte pro, you should have no trouble getting a better key from MiniDV than with Svideo footage....

Sorry, I know this is OT -- I'll shut up about y/c capture now. :)

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Old April 3rd, 2004, 10:30 AM   #284
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Move this thread to Alternative Imaging?

There's a new forum Chris has but up (Alternative Imaging) and I'm wondering if that might be a better home for this thread for several reasons:

(1) Due to it's popularity and longevity, most DVX100 users here are quite familiar with it. Juan could post results later.

(2) The technology he's developing could apply to any camera (e.g. XL1s with mini35, JVC HDV etc).

(3) Input from other "alternative imagers" might enhance the thread

What does everyone (esp. Juan) think?
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Old April 3rd, 2004, 02:04 PM   #285
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Stephen,

I think it's a good idea, either way I will post results in this forum later.

Update:

That last complete frame i posted had much less precision than 9-bits, at least in the blue and green channels...you can tell from the color shades on my hand that it's pretty decimated. The partial frame i posted before had a bit more precision.

Today I am working on fixing this problem to get the full 10-bits out of each channel, it's only a physical contact problem, but these are pins less than 0.5mm in width, so it takes some time to work with them.

The continous capture is working, so this is the only hurdle to getting the full quality video my capture card can handle. A second capture card would allow me to capture the full 12-bits per channel, but it costs ~$700 so this will have to do for now....

Will update again tonight.

Juan
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