SMART newbie question

[fmctm1sw]

I'v done some research regarding resolutions for VHS, SVHS, DVD, etc...

Here's what I already knew:
My TV can only display 525 horizontal lines on it (actually about 480). So I wondered how in the world I would get DVD (720 lines) to show on it.

Here's what I learned:
The resolution figure refers to the number of individual "blocks" each one of those 480 lines can be divided into. VHS is 240 and SVHS is 400. I fully understand that now.

My question is:
Why are there two resolution figures for DVD (720x480) and VCD (352x240)? And theoretically, it has to be impossible to convert VHS formatted tapes to DVD quality. You cannot turn 240 horizontal resolution into 720 (or 480 for that matter). Or can you?

[SLK001]

There are 525 scan lines on a NTSC television set, as you said. No matter what you do, you cannot change this. DVD has, on a TV, an EFFECTIVE resolution of 720 pixels by 480 pixels. This means that the amount of DETAIL shown on your TV is EQUIVALENT to a picture on a computer screen of 720x480 pixels. Likewise with the resolutions of VHS, VCD and SVCD.

Look at it this way... With VHS and VCD, each horizontal scan line on the TV is drawn with pieces of chalk. With SVCD, each scan line is drawn with a crayon (slightly finer than the chalk). With a DVD, each scan line is drawn with a 0.5mm graphic arts pen. The finer that you make the detail in your scan lines, the more memory space that is required (ie, higher bps) and the harder the encoder has to work (ie, processing power).

But for each case, there are STILL only 525 horizontal scan lines presented to the TV (of course, some of the 525 is overhead for the TV).

[Spicuzza]

fmctm1sw, perhaps this will help as you have touched on an area that I believe causes much confusion when understanding digital video.

First, 720x480, 352x240, 704x480, 320x240, 640x480....etc., are not resolutions in terms of optical quality. They are digital "FRAME SIZES." Pixels x Lines, 720 pixels x 480 lines, 352 pixels x 240 lines and so on.

The optical resolution of your digital video will be determined by the data rate in terms of kbps, NOT the frame size. Yes, large digital frame size 720 pixels x 480 lines coupled with high data rate 9,000 kbps can produce stunning results depending on the quality of the source material.

However, when capturing analog tape such as VHS and or Hi8 there simply is not enough data represented on those formats to be able to capture at a frame size of 720 x 480, generally a 352 x 480 quality capture encoded to 352 x 240 is the best you can achieve and at a data rate of about 2300 kbps your final project should be just under that of your source material.

Personally, I find that a 480 x 480 uncompressed AVI capture from my Hi8 camcorder encoded to compliant SVCD specifications is about the best quality I can achieve with the equipment I have.

Well, I hope this has helped as I know the term resolution is used all the time when actually referring the frame size and the immediate assumption is that to get the BEST quality you start with the DVD specifications. It simply doesn't work that way.

[fmctm1sw]

Look at it this way... With VHS and VCD, each horizontal scan line on the TV is drawn with pieces of chalk. With SVCD, each scan line is drawn with a crayon (slightly finer than the chalk). With a DVD, each scan line is drawn with a 0.5mm graphic arts pen. The finer that you make the detail in your scan lines, the more memory space that is required (ie, higher bps) and the harder the encoder has to work (ie, processing power).

Thanks for the response. But with only approx. 480 horizontal lines, how can you change the thickness of those lines as your example implies?

[SLK001]

It's not the thickness, but the detail in the scan line. Take, for instance, VCD resolution of 352x240. Each "pixel" is made of an area of 0.5" by 0.5" on your TV screen. Quite a few scan lines are part of this "pixel". This is not too difficult to encode. For SVCD, the area maybe of the order of 0.3" by 0.3". Less scan lines per "pixel" and a little more difficult to encode. For DVD, this "pixel" may be only the height of the scan line by the height of the scan line. So you see, the actual scan lines don't increase or decrease, but the effective scan lines do.

NOTE: The sizes used are for illustrative purposes only.

[fmctm1sw]

It's not the thickness, but the detail in the scan line. Take, for instance, VCD resolution of 352x240. Each "pixel" is made of an area of 0.5" by 0.5" on your TV screen. Quite a few scan lines are part of this "pixel". This is not too difficult to encode. For SVCD, the area maybe of the order of 0.3" by 0.3". Less scan lines per "pixel" and a little more difficult to encode. For DVD, this "pixel" may be only the height of the scan line by the height of the scan line. So you see, the actual scan lines don't increase or decrease, but the effective scan lines do.

NOTE: The sizes used are for illustrative purposes only.

Ok, it's getting clearer now. So each scan line may not be any different from the one before it? I'm still confused on the two numbers thing. 352x240 for VCD for example would look way better on a 20" TV vice a 50" TV then since all TV's have 525 (480 or so) scan lines. That can't be right... can it?