CTK Companion

[Andrew Phang]

I noticed on the Feautres webpage that the footage was shot progressive scan at 15fps. I'm assuming this is because it was shot with the PD100, which does p-scan at half frame rate.

My question is why? If it were meant to be a real-world professional scenario, wouldn't it be 30fps, or at least 24? What was the intention behind doing it at 15? If it's because of the p-scan, does this then mean that the dvMatte(or any keyer) isn't capable of handling interlaced footage shot with a regular dv camcorder?

[Alex Lindsay]

dvMatte works very well with interlace (test it yourself).

15 FPS is enough to begin with...and takes less time to roto...which is good for training while still acheiving a great result.

Progressive scan was used because, well, interlace stinks. We'll do some specific tutorials for interlace someday but the future is progressive scan. We don't intend to do any day to day work in interlace by year's end.

a

[Andrew MacVey]

i miss understood something you said alex, does DvMatte Work better with interlaced footage, meaning i should key before i deinterlace?

[bensyverson]

Hey yawl,

Maybe the author can chip in here. :)

dvmatte works fine on footage of any frame rate. Of course, when doing visual effects work with interlaced footage in After Effects, it's best to set up your comp at 60fps so that you can work on each field individually. Otherwise, if you work at 30fps, you risk "ghosting" the fields.

good luck!

- ben

[jarek_d_98]

I did a quick little test with my standard settings so 60i and the results were very good considering I didnt care to light the greenscreen right or place it far enough behind the subjects. Ben thanks again for creating such a good plugin. I have been very happy with DVMatte.


Rob:D

[bensyverson]

Cool! I'm glad you like it.

Just wait till you see what we've got cooking right now... it does a considerable amount more, and it's even faster than the original flavor. :)

- ben

[Faisal Naqvi]

Originally posted by bensyverson
Cool! I'm glad you like it.

Just wait till you see what we've got cooking right now... it does a considerable amount more, and it's even faster than the original flavor. :)

- ben

Oh please don't mess with our minds like that by making us drool, ben. :)

[jarek_d_98]

LOL.....oh come on give us a bigger hint than that! It's just no fair..hehe. Faster. how much faster do you need? Damn as long as it gets me there I'm happy.
My quick greenscreen had my room light on it from overhead (yellowish) and so I had a nice spot towards the top of the greenscreen then it gradated down and it still pulled a good matte. Ill try to post a picture of it. The screen was also at an angle so it would stay upright. Im thinking that is almost the worst thing you can do other than:
-leaving lens cap on
-turning all lights off
-punching a hole in greenscreen
-wearing green or for that bit using green objects


Rob:D

[astrofish]

Hi Ben,
My understanding is that one of the main things that dvMatte does to get good results from DV is to blur the chroma channel in order to give more useful chroma values for keying on.

My question is whether it does the right thing for both PAL and NTSC DV footage, since the chroma samples are very different.

If I recall correctly:
NTSC: One set of chroma samples for every 4 horizontal pixels.
PAL: One set of chroma samples for every 2x2 square of pixels, each field seperately encoded (i.e. the two vertical pixels that are combined together for chroma are from adjacent field lines, not adjacent image lines).

I just wanted to check whether dvMatte knows about the differences between PAL and NTSC DV.

Cheers - Steve Baines

[bensyverson]

Hi Steve,

dvmatte does a normal blur on both NTSC and PAL footage. This is basically to create a more uniform-looking image.

Take NTSC for example. There is, as you say, one chroma sample for every four horizontal pixels. So vertically, the chroma sample is fine. The natural reaction might be to blur only horizontally -- like a fast blur set to "horizontal." However, because the chroma information is on a grid, it actually affects the vertical image a great deal. Check out the image I've attached. The pink line represents a border before it was videotaped. As you can see, you do get perfect gradations vertically, but it's creating a kind of stairstep effect. If you do a big enough horizontal blur, you do get a smooth line -- but only in one dimension, which looks weird.

dvmatte just opts for a simple blur, which creates a more uniform-looking image, regardless of the format.

- ben