Question for Dodcap Users

[mattias]

What Dodcap receives are actually whole, progressive frames, not individual fields.

not surprising, since dv is a frame based format. the dv camera takes the two fields from the ccd, combines them into a frame, encodes it, and only splits the fields again if you're outputting a video signal. perhaps you can team up on my side in the discussion that is bound to follow that statement as soon as roger and crimsonson sees it? :-)

Whether your TV is PAL or NTSC, it will always display every other line starting with the first line

no, i'm pretty sure it actually "starts" with the second line. this is what lower field first means. look at a frame grab of some fast motion and it should be obvious. my guess is what's happening is that you're actually reading the data from the bottom of the file without even knowing it. this is how quicktime, after effects and premiere plugins work, which yook me weeks to realize when i wrote plugins for these architectures, but the plugins worked just fine all along since they didn't care about up and down...

/matt

[digvid]

Mattias -

I spent the entire evening reading everything I could find on the internet about field dominance. I also ran a number of tests on my computer, camera, and tv to see if I could find out how field dominance works.

What I have determined is that A) even though Dodcap receives whole frames, field order does matter, and B) I was doing things correctly for most systems in Dodcap even though I misunderstood exactly what I was doing.

Dodcap originally did allow the configuration of field dominance, but I removed this at the last minute because I convinced myself that it did not matter, since I was receiving whole frames. I see now that it does matter. The tests I ran tonight convinced me that my video equipment is lower-field first, and if the order of the fields in the pulldown frames is wrong, it will look jerky on the tv screen.

As you said, I was actually receiving upside down frames in Dodcap. So when I thought I was pulling out every other line starting with the first (i.e., the top field) I was actually pulldown out the bottom field! Of course, this is exactly what needed to happen to make it work on my lower-field first system, so it looked smooth to me.

I believe that almost all DV systems, whether PAL or NTSC, are lower-field first. However, aside from DV, there is no clear standard. There are some NTSC cameras that are lower-field and some that are upper-field.

The solution in Dodcap I think is to allow the swapping of field dominance. The user would not need to know specifically what the field dominance of their equipment was. They would just need to know that if they get jerky motion with the interpolated pulldown, they can swap the order to fix it.

I will add this to the upcoming release and put a note in the software that points this out.

I guess I learned something new today!

- Jeff Dodson

[mattias]

even though Dodcap receives whole frames, field order does matter

that's because the frame is split again by your camera before it's output to your tv. the incoming frame can safly be treated in every way as a progressive image if it has been scanned from film. you only have to worry about field dominance for the pulled down output.

As you said, I was actually receiving upside down frames in Dodcap. So when I thought I was pulling out every other line starting with the first (i.e., the top field) I was actually pulldown out the bottom field! Of course, this is exactly what needed to happen to make it work on my lower-field first system, so it looked smooth to me.

cool. good luck in your further work.

now, how can we solve andreas' problem? :-)

/matt

[digvid]

Mattias -

I think the way to solve Andreas problem is to modify Dodcap to allow toggling the field dominance. There are already hooks in Dodcap to allow this, so it will not take long to add it.

Of course, this assumes that the jerkiness he is talking about is actually due to a field dominance issue.

Andreas, if you are listening, I could build a special version of Dodcap that allows you to toggle the field dominance and we could see if this solves your problem. Are you interested in experimenting with this?

- Jeff Dodson

[Andreas Wideroe]

Andreas, if you are listening, I could build a special version of Dodcap that allows you to toggle the field dominance and we could see if this solves your problem. Are you interested in experimenting with this?

Jeff, I'll be more than happy to do some test for you. Also, if you like I can send you a CD or two some raw films so you can have a look for yourself?

Maybe it would be good for you to do some tests with PAL stuff in addition to your standard NTSC?

Andreas

[digvid]

Andreas -

Well, I do test the PAL pulldown patterns. However, I don't have the means to test with an actual PAL camera. All I can really do is create NTSC DV files with PAL pulldown schemes.

Also, the pulldown schemes I am using were tested initially by PAL users, because I wasn't sure what would work well, and what the "standard" was for PAL schemes.

Regarding the files you have applied pulldown to, why don't you post one on your ftp site, and I will download it and take a look?

I will post a link on my web site today (this evening for you) with a new install that allows you to toggle the field dominance. This should help you determine whether we are seeing a field dominance issue or if you just perceive the patterns as being jerky.

The tricky thing about field dominance is that it seems to depend on the video camera. About half of all Dodcap users right now are PAL people, and I know of a few specifically that are using the interpolated pulldown, and they all seem to have lower-field dominant cameras, like mine. I think it just depends on the camera or other video equipment you are using. At least this is what I gather from the research I have done.

- Jeff D.

[digvid]

For all those who are interested in a batch processing module in Dodcap: How would you like this feature to work? I realize this is a broad question. However, it is very difficult for me to design this module without knowing how most people are organizing their capture files on their hard drives right now.

When you apply pulldown to files right now, where do you place the pulldown files in relation to the original file? In the same directory? Do you create a special folder just for your new pulldown files? That is the type of information I would like to know.

Later!

- Jeff Dodson

[Barry]

I'm sure everyone will have their own preference, but my suggestion would be to append _pulldown after the name and keep it in the same folder. So video1.avi would be become video1_pulldown.avi after the pulldown. You can move it to any folder you want afterwards.