Digital8 Capture vs DV capture

[Nikos]

Is DV capturing generally uncompressed? If so, how much theoretically is DV better than Digital8 capturing in terms of quality?

Are there any statistics for these two formats anywhere?

[Nikos]

bump ?

[ahfairley]

You are recording the same digital data to tape with either system, so it's the same on mini DV or digital8. DV is compressed, but I can't remember how much.

[Nikos]

Does this mean that using the digital8 format, an 8mm recorded tape will look exactly the same as a hi8 recorded tape (digital8 format)?

[TuxOmatic]

Does this mean that using the digital8 format, an 8mm recorded tape will look exactly the same as a hi8 recorded tape (digital8 format)?

No. Now you are changing things. When comparing mini DV to Digital8, the format of the video after sending it to your computer is the same. The quality of the video, as far as sharpness and clarity, will depend on the camera, lens, chipset, etc. If you have a 8mm tape that was used in a 8mm camera and you put it into a Digital8, you can play it with the camera, but you can't transfer it as a digital file to your computer. 8mm is analog with a lower resolution. You can connect your 8mm camera to your Digital8 camera and copy the video to digital, but that won't improve the quality of the video (garbage in, garbage out). Also, you can record on a 8mm tape with your Digital8 camera, creating a digital file, but Sony doesn't recommend it. The quality of your video will be lower due to the make-up of 8mm tape.

[jtor]

If you have a 8mm tape that was used in a 8mm camera and you put it into a Digital8, you can play it with the camera, but you can't transfer it as a digital file to your computer. 8mm is analog with a lower resolution.

...actually, some Digital8 camcorders will let you do just that; transfer analog video to your computer thru firewire. I know for a fact that TRV410 (an old model) can do this. You just need to check the specs of the D8 cam if she's capable.

[Nikos]

Since I would record a television program off my Digital8 format/camera, would it still record the same lines of resolution on an 8mm as well as a Hi8 tape?

I know Hi8 records up to 400 lines of res, and 8mm records 250 lines of res, but do these numbers even apply if I am using the Digital8 format?

[Xesdeeni]

Lines of Resolution Tutorial

Definition

Lines of Resolution is a term used to quantify the clarity of an image meant to represent a real-world scene (http://members.aol.com/ajaynejr/vidres.htm#Quick). It is an analog measurement. It is normally measured by using a set of alternating black and white lines which get progressively smaller along a graduated scale (http://www.bealecorner.com/trv900/respat/#EIA1956). Where the lines blur into a gray, the annotated value can estimate the lines of resolution for a particular device.

Lines of horizontal resolution refers to the number of vertical lines that can be represented in an image. Lines of vertical resolution would refer to the number of horizontal lines that can be represented.

Since the aspect ratio of various imaging methods varies widely, the definition of lines of resolution is normalized for a square (some references say circular (http://members.aol.com/ajaynejr/vidres.htm#Circle), but the concept is the same) image, a.k.a. "one screen height." So, for example, when measuring the lines of horizontal resolution for a 4:3 television, the total number of lines visible across the entire screen would have to be multiplied by 3/4 to get the lines of horizontal resolution.

Analog

Take a VHS tape as an example: The bandwidth of VHS is about 3.2MHz (http://repairfaq.cis.upenn.edu/sam/icets/vcr.htm). For NTSC, there are 29.97 frames of 525 lines each second (http://www.ee.surrey.ac.uk/Contrib/WorldTV/compare.html). So there are 3.2MHz / (29.97 * 525), or about 203 cycles per line. Only about 80% of each line contains picture (the rest is used for synchronization), so that leaves about 163 cycles per visible line. For lines of resolution, each cycle would contain a black and a white portion, for a total of about 325 visible transitions (vertical lines) per scan line. Adjusting for the screen height equivalency (3/4), leaves about 244 lines of resolution.

Note: The oft-quoted 240 lines of resolution for VHS is also often confused with the number of scan lines. However, VHS video has the same number of scan lines as all other (compatible) formats.

The lines of vertical resolution are a bit more difficult to quantify. It is important to realize that all compatible television devices have the same number of scan lines (525 for NTSC, where about 486 of them contain video; 625 for PAL, where about 580 of them contain video). As a result, most devices have approximately the same lines of vertical resolution. Because of this similarity between devices, most of the time the lines of vertical resolution measurement is ignored today. As a result, the term lines of resolution now normally implies the more important lines of horizontal resolution.

Note: Although most devices have about the same lines of vertical resolution, this value is not the seemingly obvious 480/576 value. Due to an effect called the Extended Kell Factor, the lines of vertical resolution in actuality is lower than this. The effect is essentially the same as the issue when comparing digital video resolution to analog video lines of resolution. See the next section.

Digital

It is not as easy as it seems to compare digital resolution to the analog lines of resolution. Most people think that the number of pixels is exactly equivalent to the lines of horizontal resolution.

First, the "screen height" ratio must be used. For example, the DVD format contains 720 pixels per line. However, only 720 x 3/4 = 540 pixels are in a width equivalent to the screen height for a 4:3 display. For a 16:9 display, only 405.

But there is another, often missed factor that affects the comparison as well, known as the Extended Kell Factor (http://members.aol.com/ajaynejr/kell.htm). Assume that you are going to display 540 black and white lines. If they line up with the pixels, all is well. But what if there are 539 lines? 541 lines? Here is an example of what will happen with slightly fewer or slightly more lines than pixels: http://members.aol.com/ajaynejr/resol2.gif. Since the input is an analog waveform, even though it may be limited in how many lines it can hold, it is not limited in how those lines are aligned! So the number of pixels does not equal the lines of (horizontal) resolution.

If we halve the number of lines, then the digital device can certainly represent this reduced number of lines. So the relationship between the number of pixels and the lines of resolution lies somewhere in between. The fraction of the digital resolution at which all the lines become visible is called the Extended Kell Factor. It depends on factors like filtering, analog-to-digital conversion technology, and others. But the bottom line is it also depends on when an individual's perception of the image can distinguish all the lines. Since this is a personal perception issue, there is much debate about the actual value of the Extended Kell Factor itself.

Note: The Extended Kell Factor is also a player when determining the lines of vertical resolution for all video format. This is because the scan lines are discrete entities, just like the pixels of a digital device.

And Now Back To Our Story

Since you say you will record a television program on your camcorder, I assume you mean the camcorder has an analog input that you will use to record the program.

In this case, your digital8 camcorder will record the video digitally (I don't think any of the digital8 camcorders can also record Hi8, they can only play it back...I don't know about 8mm compatibility). The lines of resolution that you actually capture will depend on:

1. The quality of the source video (DVD will be better than over-the-air, which will be better than VHS, etc.)
2. The quality of the source video playback component (all DVD players are not created equal, for example)
3. The type/quality of your analog connection (S-Video will be better than composite)
4. The quality of the analog decoder in the camcorder
5. The quality of the compresion chip in the camcorder

So how many lines of resolution is a function of the worst qualities of each of these. If your source is VHS, then you cannot expect more than about 240 lines of resolution. Over-the-air video provides about 330 lines of resolution, while SVHS provides about 400 lines of resolution. A DVD player is normally listed as providing about 500 lines of resolution (but this is a misnomer--see above).

It is likely that the analog decoder will be of sufficient quality to handle any of these. Theoretically, 720 digital pixels is roughly 415 lines of resolution (see above), so all of the above sources should be handled.

Xesdeeni

[Nikos]

Normal cable broadcast is only 330 lines of resolution?

[Xesdeeni]

(((4.2MHz / (29.97 * 525)) * .8 ) * 2) * 3/4 ~= 320 lines of resolution.

This means about 426 visible lines per scan line. So applying an (conservative) Extended Kell Factor of 1.3 means that it would take about 550 digital pixels to represent one over-the-air scanline.

BTW, this also explains why 352 pixels per line isn't quite enough, even for VHS: 244 * 4/3 * 1.3 ~= 423 pixels

Xesdeeni

[Edited to remove inadvertent smiley made by 8 )]

[yg1968]

Thanks Xesdeeni for the very informative posts.

[MagmaManno]

Dang, my head hurts now...

Magma

[Nikos]

I am a little confused Xen..I have a Sony DCR-TRV320 Camcorder I use to record cable (televison with). That has enough to capture most of the information (if not all of it technically right), altough the picture might not look as good as the ORIGINAL television broadcast.....

So its ok to use the digi cam right for televsion recording?

[Nikos]

While we are on the subject, how does satalite compare with cable in terms of quality and lines of resolution?

[Nikos]

bump ?

[BJ_M]

do a search here on the forum -i posted a lenthy comparison of the two already

[Xesdeeni]

Nikos,

That depends on the channel. They vary the resolution and bitrate of the channels. They also pre-filter the channels to reduce noise and detail and make it easier to compress.

I assume it is a $$$ thing. The bigger networks probably get more bandwidth. And I understand the best quality is for the pay-per-view. This is probably 1) to keep you paying for the next pay-per-view, and 2) because the content can be encoded offline (not real time), so the quality can be better.

So some channels probably look better than analog cable. But unfortunately, for my taste anyway, most channels look worse. I would personally rather see a light analog noise across the whole image (or course my analog cable doesn't always have a "light" noise), than see halos and other MPEG artifacts around moving objects over a static background, or complete breakups of the image as the scene pans (I read in the propoganda from one of the satellite services that the human eye can't see such things in moving images...boulderdash!) or over-filtered (take a look at the Golf channel and see greens with no discernable detail), over-compressed, reduced-resolution MPEG. I love digital video, but the implementation in this case is poor.

Xesdeeni