Lines per inch really doesn't apply to video. It's best to just forget about the concept all together so you don't confuse yourself in the future. Lines per inch only applies to a format such as hard copy prints or scanners, where the objects have a fixed physical size.

In video, the important factor is resolution. For example, NTSC DV is 720x480, whether viewing it on a 3 inch monitor or projecting it on a 30 foot screen. Since the image size is approximately 4:3, you can see that you won't have the same number of pixels per in horizontally as vertically anyway.

Now, if you're planning on scanning some pictures to use in a video presentation, then you can choose an appropriate scanner dpi to get an image close to the video resolution. If you're scanning 4x6" prints, then using a resolution of 150dpi will result in a 600x900 image, which is just right for allowing a little cropping when adding it to the timeline.

I came across the following:

"The latest innovation in digital imaging is digital video (DV). DV’s greatest advantage is the sharpness of the picture. On a standard scale used to measure video clarity, a VHS recording has 240 lines of horizontal resolution, while broadcast or cable television have a maximum of 330 lines. High-resolution home camcorders (Super VHS and Hi-8 formats) boast between 400 and 425 lines of resolution, provided they are connected to a television using separate audio and video inputs, rather than a single-line radio frequency (RF) connection that combines the audio and video. The new DV camcorders record a picture with 500 lines of resolution."

I am confused. But would like some kind of explanation, otherwise I will drive myself nuts.

The explanation you are dealing with is always confusing to everybody. It involves quite a bit, but comes down to the following:

In the conventional description of DV, there are 720 dots on each line of 480 horizontal lines in the DV format. These lines are NOT what they are talking about.

Imagine each of those 720 dots being stacked, one on top of each other for 480 times. The effect is 720 lines going up and down. VERTICAL lines.

From early days of TV, when they used to actually broadcast the "Test Pattern," quality of a signal was defined as follows:

Take the center 75% of the screen and divide it into lines going up and down. They took the center 75% because it was the clearest area. The left and right edges were not nearly so clear, especially in the old days. The lines were alternating black and white.

The thiner the lines, and the closer together they were, the harder they were to tell one from the other. If they all blured together, there wasn't much quality, but if they were sharp and clear, the picture was judged by the number of fine lines, close together, that you could count on a "monitor" at the signal source.

From a technical standpoint, take the 720 vertical lines in the definition of the DV Standard, and multiply it by .75 (75% center). The number is 540.

If you have a PERFECT picture, you can see 540 distinct lines. Most, if not all decent Mini-DV camcorders can "resolve" at least 480 lines. Many, especially the better ones, can resolve 520. Recently, I have seen units advertising 530, and even 540 lines of resolution. Nice and sharp.

The VHS and other numbers come from the maximum number of lines visible in THOSE systems. That 240 lines, which was quite impressive, once upon a time, is rather sad by today's DV standard.

On the other hand, in true HDTV, with 1920 x 1080i, the goal will be 75% of the 1920. In otherwords, 1440 vertical lines would be a most excellent HDTV resolution. Just a coincidence, I suppose, but that 1440 is exactly twice the total number of dots POSSIBLE with 720 x 480 DV.

wcoxe1,

If you count 540 pixels across (75% of the screen), how can you resolve 540 transitions from black to white if a pixel can only be one color or the other?

You might never see 540 lines, since you only count the black ones, eh?

Wondering, mph

A white line is a white line. A black one is a black one. I have no trouble counting either.

Try this for a detailed but somewhat convoluted description.
http://members.aol.com/ajaynejr/vidres.htm

What always fascinated me was how a TV picture is actually painted on the screen one line at a time and that the process is interlaced meaning that every other line is skipped, then it goes back to do the other lines. So the pixels are painted left to right every other line one sweep after the other at roughly 60 screen fulls a second, left to right so your eyes are tricked into thinking it is seeing a moving picture, when in fact it is rather different. Hope I got that right, too lazy to check specifics, goes back to when I built my Heathkit color TV. Those were the days and a rush, when you plugged it in and it actually worked without burning the house down.

Hi All,

Here's more food for thought:

"The DV format has a native pixel resolution of 720 x 480 but 720 lines of pixels do not translate to 720 lines of resolution. This is because if you were to display 720 lines across the screen, they would have to be right next to each other and therefore indistinguishable as lines. One formula to arrive at maximum 'visible' line resolution is to multiply the horizontal pixel value by .7. By doing that you get a maximum possible line resolution of 540 for the DV format. It's all a bit confusing because lines are also used synonymously with pixels in denoting resolutions, but that usage is different from the use of lines as a measurement for horizontal resolution which refers to 'visible' lines. In any case the whole horizontal lines of resolution thing is really a kind of mess because there is not a consensus on the math used to calculate it so pixels are a more certain measurement."

From:
http://video.multimedian.com/school/digitalfilmmaking.html

This is a fairly accessable article, I haven't surfed the site, but it looks like it might be helpful for some basics.



Regards, MPH

Can someone relate the actual lens performance which have always
been rated in lines per millimeter resolution to the DV performance
in pixel resolution? As it seems to me the pixel resolution is
the final link in the chain.

James J. Kizak

James, that depends on the quality of the lens and the size of the CCD that the lens projects the image on and how many CCD chips the camera contains. I would say though that since half-frame 35mm film has a resolution equivalent of around 3000 lines vertically, and the best HDTV systems are only 1200 verticaly, that the lens is far from the weak point in the link. DV is 480 pixels vertically. That's what you've get, 720x480 pixels. There's no per millimeter anything involved.

Chienworks:
Thanks for the info. I was just wondering out loud if someone
had come up with a formula to equate the two, like 480 pixels
is equivalent to 300 lines per millimeter, mainly to give
the "old film guys" something to reference to.

James J. Kizak

James, AH-HA!!! Now i see what you're after. As i mentioned, half-frame 35mm is commonly considered to have about 3000 lines resolving power, although this varies widely with the type of film, ISO speed, processing, etc. Since a half-frame is 18mm high, you could say it has about 167 lines/mm. So, a DV frame is about the same resolution as a 4x3mm piece of movie film, or a little better than half that of the ol' 8mm stuff. Sounds pretty sad, huh?

Chienworks:
Thats great. I can see how the ISO and processing can affect
the outcome and even confuse it. I always wondered when the
Digital was noise free how it equated to film.

James J. Kizak

>>One formula to arrive at maximum 'visible' line resolution is to multiply the horizontal pixel value by .7. By doing that you get a maximum possible line resolution of 540 for the DV format.>>

Is it the display, the camera or the DV tape stock then that determines how close to this maximum you can achieve? I assume that all of those would affect the DV resolution. I would think that some cameras aren't optimized to give the full 540, and if the camera (and stock) is able to maintain it, then I guess it could still be degraded depending on the quality of the display monitor or TV.

Finally, if one camera rates at 540 and another rates at 500, is there much of a difference on a standard NTSC monitor?