How does the video format work on camcorders?

[neo265]

Im curious to how the sensor captures footage. I have a PAL MiniDV camcorder which I know captures 25fps interlaced over 50hz. Because its interlaced, is it capturing 50 seperate fields per second (making it technically 50fps) or are the fields that make up a frame the same image, just odd and even rows?

Does the sensor capture the image progressivly and the processor converts it to the correct format?

It would actually be great if someone knows where to find some detailed explanations of how this works.

Thanks

[guns1inger]

the same image, just odd and even rows

But 1/50th of a second apart, hence the interlacing lines you see on a progressive display like a PC.

Most older cameras capture 50 fields per second. Some newer DV cameras can do progressive, as do most HD cameras.

Some starter reading : http://en.wikipedia.org/wiki/DV

[neo265]

Thanks for that, Ive been to Wiki and How Stuff Works and they dont explain the capturing side of things.

Most consumer camcorders (the one in my price range) are only able to capture an interlaced image. So they do capture 50 seperate fields then? Sorry Im a bit confused by your explanation.

[guns1inger]

Yes, 50 separate fields per second

[gadgetguy]

Put another way. Every 1/50th of a second, the camcorder captures a half frame, or field. So every 1/25th of a second you have 2 fields making up a whole frame, but the two fields come from two separate moments in time, one containing the odd scanlines, the other containing the even ones. This is why interlacing is obvious when viewing the whole frame in motion scenes where there is drastic change between one field and the other. Because the two fields come from different moments in time it is important to maintain the field order throughout processing and also why deinterlacing results in degraded detail.