progressive or interlaced for stills

[Terry Lyons]

well my decision has gone from xl1s to dvx 100a to pd 170. right now I am looking to buy probably the 170 although does it shoot in 30p and if not will I be able to pull stills from the frames or would the dvx 100a shine because of its progressive mode for an occasional still. The specs for the 170 say it only shoots 480p for stills, what that means I dont know.n Thanks again TL

[Alan Christensen]

Progressive mode for stills is much better than interlaced. With interlacing, each frame is made up of two fields that are captured 1/60 of a second apart. The first field contains all the odd lines in the frame and the second field contains all the even lines. If there is any movement in the picture during the time between when the two fields are captured, then you will have what is essentially two different pictures superimposed on each other. This is unacceptable for stills, so interlaced frames must be de-interlaced in order to use them as stills. De-interlacing basically throws out one of the fields, for example all the even lines in the frame, and then replaces them with new even lines that are interpolated from the odd lines. This essentially limits your effective vertical resolution to 240 lines of resolution, rather than the 480 lines that you would ordinarily get from an interlaced frame.

When you shoot in progressive scan mode, the two fields are captured at the same time. There is no need for de-interlacing and you preserve all the vertical resolution that the DV format allows.

The PD-150 does shoot progressive scan video, although it is only 15 full frames per second. This makes for unacceptably jerky "live" video, but is just fine for capturing stills. I would expect the PD-150 stills to be as good as the DVX-100a stills, assuming both were shooting in progressive scan mode. The DVX-100a would have a slight advantage in that it shoots 30 frames per second rather than the 15 frames of the 150. This means that you would have more individual frames to choose from per second with the DVX-100a. However, for most applications where you want to choose stills from video, 15 frames per second is plenty.

Hope this helps.

[Boyd Ostroff]

Another solution is to shoot regular 60i and use an adaptive de-interlacer afterwards, such as DVFilmMaker, Magic Bullet or Joe's Filters for FCP. These programs attempt to have the best of both worlds by handling areas of the image with motion differently from static areas. They do not just throw away alternate fields like the simple deinterlacing Alan describes. They can produce a pretty good facsimile of 30p video in most cases. Downside is that rendering is required.

Do a search here on "deinterlacing" and you will find lots of info.

[Terry Lyons]

Thank you guys very much. It looks like the still ability of either cam shouldn't play much of a role in the decision of one cam over the other. Now the 30 or 24p thing over 60i for better quality video is the next hurdle, althought watching the tele seems to have alot of 60i that looks good. Probably most are 1/2" ccd's but maby some are 1/3's I don't know. Being my first purchace in this level is hard as I don't have any first hand knowledge of what they both look like on the monitor.

I have seen some really nice stills made from 30p but don't know of any deinterlaced to look at.

As far as video the only stuff I have seen has been on the computer and it is hard to get a good representation because of compression, how it was shot, etc.

There is definate bias between both groups but at this point that is all I have to go on. Here in Bakersfield the stores dont cary either one so it is hard to go check it out. Any thoughts are very appreciated.

[Mike Rehmus]

I believe that if you shoot stills to the memory stick with the 150/170, it automatically runs in progressive mode.