What does TV lines refer to?

[Doug Turner]

Hi all,

I've searched high and low for a layman's answer to what sound like it should be a simple question...

If I'm shooting PAL 720x576, then this is the size of the picture captured in pixels. Simple.

So the question is, my camera states it has 700 TV lines (horizontal resolution) - what does this refer to?

And another question - Nbr of Effective pixels is 752x582... does this mean the pixels in the camera don't relate 1:1 to pixels stored on DV tape? Or does it use the extra pixels for image stabilisation?

TIA, Doug.

[Graeme Nattress]

"TV Lines" resolution has how resolution was measured before digital. Basically you print some sharp,vertical, alternating black and white lines and video them, and count how many clear lines you can see through the system being tested. The lines being vertical therefore measure horizontal resolution.

However, in consumer camera specs, these line measurements need to be taken with a pinch of salt. You don't know wether they refer to the lens, the ccd, the camera output direct to a monitor, or recorded onto DV tape and played back. And you don't know if the lines were actually measured, or because you've got 720 vertical lines in the digital format (and a few at the left and right don't get used) you've got 700 left, and that's what they're stating as resolution.

In reality, you'll be lucky if you can get 500 lines out of the camera, and certainly around that after the filtering that goes on with the DV codec. But don't worry - all DV cameras are about the same. Some high end ones may have lenses and CCDs that can pass through a higher resolution, but it will get dropped to the same as the rest as soon as it gets recorded to tape. Old betaSP cameras were also like this, quoting wonderful resolution figures which dropped to over 400 lines as soon as they get recorded to tape.

However, starting with a higher real resolution does help the recorder part of the camera produce a better picture.

Hope that helps,

Graeme

[Norm Couture]

Doug,
"TV Lines" refer to the horizontal resolution measured in relation with the picture's height. That is, for a standard 4:3 aspect ratio, your 720 pixels accross the screen divided by 4/3 would give a max of 540 TV lines in theory. That's the highest resolution possible from a DV recorded tape. But many camera heads (lens and CCDs) are capable of much more (700 in your example) before going through the processor that digitizes the signal to the DV standard of 720 x 576 (PAL) or 720 x 480 (NTSC).

In short, the more resolution you've got to start with from the optics and CCDs, the sharpest picture you'll have once encoded to the DV standard of 720 x 576.

[Doug Turner]

Thanks for the answers, guys.

I'm assuming that if I capture directly onto my PC via firewire that I won't be improving quality (as opposed to recording to tape and then capturing).

What's stopping me hooking up a nice little laptop to my camera in the field and recording straight to hard disk rather than faff (technical term) around with tapes?

I'm not a wedding doco or dogme-type, so placing a stool (backless chair) next to the camera tripod with a laptop on it and clicking capture instead of hitting record on camera isn't too much of a hassle.

[Glenn Chan]

For purchasing decisions, it makes the most sense to look at the output from the cameras tested so there is little room for manufacturer fudging. Even numbers from one manufacturer can be misleading.

Some consumer cameras are noticeably not as sharp as others. Some people find this softening acceptable and even desireable. A higher resolution camera with a softening filter (in front of the camera or in post) would likely produce better results though (could maintain sharpness and softening).

The following Japanese site has frame grabs from various consumer cameras.
http://babelfish.altavista.com/babel....html&lp=ja_en

Caveats:
1- Your computer monitor is probably very inaccurate in terms of color reproduction.
2- Looking at images might lead you to ignore the larger picture (sound, size, ease of use, etc.).
3- You might like the cameras which are more contrasty and saturated. On some of the more expensive cameras this can be adjusted so you may like them more when contrast and saturation is boosted.

As far as capturing to a laptop, you probably will not gain extra resolution doing so. The analog circuits in the camera (and your capture device) have to be good enough to avoid degrading the video and everything before the DV codec has to be able to support more resolution than the analog-->DV conversion circuits.

[Rob Lohman]

You will not gain any quality by capturing directly to your laptop
or any PC for that matter. The only advantage is longer recording
times and saving wear and tear on your camera (although I would
run a tape as a backup personally).

The downside is having to lug a machine around (with enough
battery time!!!) and a possability you drop frames.

Since DV is fully digital it won't matter if you store it on tape or
on harddisk. The quality is exactly the same. If you where to
capture to harddisk and record to tapen and then capture that
after the event and compare frames they will be 100% the same
(bar recording/reading problems on tape or dropouts on the
harddisk)

[Norm Couture]

Doug,
Back to the last question of your first post.
Picture the CCD of a camcorder as a wall made of small light-sensitive tiles. The more tiny tiles you can stick on your wall, the sharpest picture you'll have. BUT, the more tiles you have, the smaller they must be. And smaller "tiles" will capture less light, so you'll have poor low-light performance.
It's all a matter of compromise...

As for the "effective pixels" ratings, there's one for the still pictures taken to the memory card, there's another one for the video to be transcoded to DV tape, and the extra pixels may be used by an electronic stabilizer that will constantly "recenter" the picture to reduce the shaking.

[Miguel Lombana]

On a similar question, I'm looking for a new monitor for my editing system. I currently use 2 NEC LCD1530v PC monitors for the NLE side of the system and a very old Panasonic CT-1390V monitor for reference and playback.

Now I've been looking at several of the new low priced LCD units at Walmart and Target and no where do they offer a "lines" of resolution statement on their documentation. Are we at a point where we are only able to purchase by pixel and not lines on these units?

What should I be looking for "IF" I were to go in this direction, mind you I'm not convinced that this is the best solution as my nice CRT really shines in picture quality however space has become an issue.

Thanks in advance,
MIGUEL