Author Topic: Why modern analog cameras still using TVL(Television-Line) as a spec?  (Read 2105 times)

0 Members and 1 Guest are viewing this topic.

Offline zajusakoTopic starter

  • Newbie
  • Posts: 2
  • Country: us
Hi all.
I understand this value is from old line-scan cameras/TVs, so why modern CCD/CMOS based analog CCTV cameras still using TVL? And why don't that value equal the vertical pixel count?
Thank you.
 

Offline tooki

  • Super Contributor
  • ***
  • Posts: 13156
  • Country: ch
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #1 on: February 17, 2019, 05:50:25 pm »
"Lines of resolution" is the granularity in the horizontal.

For example. NTSC is 525 scan lines, of which historically around 485 are actually visible (due to overscan), which is why we chose 480 in digital standards for SD.

The number of scan lines is fixed, as it is a fundamental characteristic of the analog signal format. So when we look at a stated spec like a standard VHS VCR having about 300 lines of resolution, it means that in each scan line, the VCR can resolve down to about 300 lines. But the key thing to remember is that it's analog, so there are no pixels. It's a continuous value within each line. Whether this signal originated in a vidicron tube or a CCD, the analog signal is still this analog signal.
 
The following users thanked this post: videobruce, Richard Crowley

Offline dmills

  • Super Contributor
  • ***
  • Posts: 2093
  • Country: gb
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #2 on: February 17, 2019, 09:38:33 pm »
TV Lines is also a very useful measure when you look at a whole camera system, in particular with a modern HD or 4k chain, the glass on the front can be a significant limiting factor (particularly as you crank the iris open in low light conditions).

Just because my sensor can manage 3840 pixels or whatever does NOT mean that I can resolve that by the time the prism block & lens have done their thing.

Regards, Dan.
 
The following users thanked this post: tooki

Offline tuzakeyiwe

  • Newbie
  • Posts: 2
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #3 on: April 25, 2019, 10:01:18 am »
TV Lines is also a very useful measure when you look at a whole camera system, in particular with a modern HD or 4k chain, the glass on the front can be a significant limiting factor (particularly as you crank the iris open in low light conditions).

Just because my sensor can manage 3840 pixels or whatever does NOT mean that I can resolve that by the time the prism block & lens have done their thing.

Regards, Dan.

CCTV camera bodies also have that spec, and this is a mystery for me for a long time...
 

Offline videobruce

  • Frequent Contributor
  • **
  • Posts: 476
  • Country: us
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #4 on: April 25, 2019, 12:29:53 pm »
The Chinese CCTV industry appears to use the resolution of the actual sensor, not what the final video output actually is. Which is why these grossly inflated numbers (typical marketing lies) come from. Mostly noticeable with old school analog cameras calming up to 800 lines when the NTSC limit is 480 (more or less as stated).

One look at these so-called hi-res cameras on a high res display (1080p or even  a 720) clearly shows that is a lie.
 

Offline tooki

  • Super Contributor
  • ***
  • Posts: 13156
  • Country: ch
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #5 on: April 25, 2019, 04:30:24 pm »
The Chinese CCTV industry appears to use the resolution of the actual sensor, not what the final video output actually is. Which is why these grossly inflated numbers (typical marketing lies) come from. Mostly noticeable with old school analog cameras calming up to 800 lines when the NTSC limit is 480 (more or less as stated).
That’s not what lines in analog video specs mean.

As you can imagine, the number of scan lines is fixed (525 in NTSC, 625 in PAL), with a fair number at the edges lost to overscan (and some mandatory blank lines, etc), resulting in the ~480 visible lines. We are still talking about scan lines, that is, the lines going from left to right, aka the vertical resolution.

On the other hand, as analog standards, there is no fixed horizontal resolution in NTSC/PAL/SECAM, since it’s a continuous analog signal for each line. So when we say that S-VHS gets around 400 lines, laserdisc 450, broadcast 350ish, and regular VHS only about 250, we are talking about the horizontal resolution. And this is why DVD looked so good: it does 720 lines. 800 is eminently possible, though it requires exceptionally good cabling and signal processing. Only broadcast monitors could do anything close to that.

As for how it’s calculated, it means that when recording a test chart, you can make out that many alternating black/white lines (hence the starburst test patterns).
 

Offline videobruce

  • Frequent Contributor
  • **
  • Posts: 476
  • Country: us
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #6 on: April 26, 2019, 07:05:57 am »
But with a max of 480, resolution numbers above that (up to and over 700L) as these no-name companies advertise are basically meaningless.
 

Offline helius

  • Super Contributor
  • ***
  • Posts: 3688
  • Country: us
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #7 on: April 26, 2019, 07:36:37 am »
Tooki is on the money, except that the lines of resolution (LOR) is actually measured with respect to a horizontal distance equal to the vertical height. So it measures the horizontal resolution, but the result is scaled to the same units as the vertical scan lines. 480 lines of resolution is approximately square "pixels", although they are not addressed as actual pixels in an analog signal. Broadcast resolution is higher, with approximately 540 lines.
Broadcast quality digital VTRs like the D1 use non-square pixel frame formats to achieve this level of resolution. They have higher horizontal resolution than vertical, with a "lines of resolution" over 480.
« Last Edit: April 26, 2019, 07:38:40 am by helius »
 
The following users thanked this post: tooki

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 7854
  • Country: au
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #8 on: April 26, 2019, 08:00:44 am »
Resolution lines are nothing to do with the scanning lines, except in analog TV where the vertical resolution is limited by the number of scanning lines which are available for viewing.

Resolution lines were used in photography many years prior to TV.

Telecines & "Flying Spot Scanners" (FFS) were a common video source for displaying resolution charts in TV.
In this case, the charts were supplied in the form of slides.

You can use a resolution slide with a plain old optical projector, as I did years ago with the one from the FFS at my old work.
I had purchased, at great expense, a "Kodak Carousel" slide projector, & wanted to check it against my old unit.

It was astounding!
The Kodak showed the resolution lines, both vertical & horizontal, out to "near as dammit" the limit of the original photographic process used to make the slide.(My old projector horrible in comparison)

I then fired up the FFS.
It was very good for a TV picture, but it looked crappy compared to the direct optical image.

 
The following users thanked this post: tooki

Offline helius

  • Super Contributor
  • ***
  • Posts: 3688
  • Country: us
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #9 on: April 26, 2019, 12:03:07 pm »
Resolution lines were used in photography many years prior to TV.
This is also true, but that is a subtly different sense of the concept of "resolution". Resolution in photography (and printing, and microscopy) is in lpmm (line pairs per mm): How many pairs of light and dark lines per mm can be clearly seen. The military had an obvious interest in aerial reconnaissance photography, and developed the standard test target: https://en.wikipedia.org/wiki/1951_USAF_resolution_test_chart
This is an empirical test, but does not fully characterize the actual physical process that limits resolution. For that you need to find the MTF which is a spatial frequency response function.

By contrast (no pun intended), TV resolution lines is not a measurement of spatial frequency, but of signal fidelity. There are no mm here, as the video picture does not have a concrete size; instead it is an abstract object with dimensions in megahertz.
 
The following users thanked this post: tooki

Offline tooki

  • Super Contributor
  • ***
  • Posts: 13156
  • Country: ch
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #10 on: April 26, 2019, 01:48:18 pm »
Tooki is on the money, except that the lines of resolution (LOR) is actually measured with respect to a horizontal distance equal to the vertical height. So it measures the horizontal resolution, but the result is scaled to the same units as the vertical scan lines. 480 lines of resolution is approximately square "pixels", although they are not addressed as actual pixels in an analog signal. Broadcast resolution is higher, with approximately 540 lines.
Broadcast quality digital VTRs like the D1 use non-square pixel frame formats to achieve this level of resolution. They have higher horizontal resolution than vertical, with a "lines of resolution" over 480.
Thanks for the added info! I had (naively?) assumed it measured across the whole video line.

I’ll agree that 800 lines within 3/4 of a video line is, um, optimistic. But in pure theory I suppose it’s possible!
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 7854
  • Country: au
Re: Why modern analog cameras still using TVL(Television-Line) as a spec?
« Reply #11 on: April 27, 2019, 03:53:11 am »
Resolution lines were used in photography many years prior to TV.
This is also true, but that is a subtly different sense of the concept of "resolution". Resolution in photography (and printing, and microscopy) is in lpmm (line pairs per mm): How many pairs of light and dark lines per mm can be clearly seen. The military had an obvious interest in aerial reconnaissance photography, and developed the standard test target: https://en.wikipedia.org/wiki/1951_USAF_resolution_test_chart
This is an empirical test, but does not fully characterize the actual physical process that limits resolution. For that you need to find the MTF which is a spatial frequency response function.

By contrast (no pun intended), TV resolution lines is not a measurement of spatial frequency, but of signal fidelity. There are no mm here, as the video picture does not have a concrete size; instead it is an abstract object with dimensions in megahertz.

The only reason it may be expressed in MHz in TV use, is because the scanning line in an analog TV system takes, (for 625 & 525 line systems) approx 64 u/s to complete a scan.("spatial frequency" is a somewhat esoteric concept which has no real place in TV standards).

A sharp black to white transition (or vice versa) produces an electrical signal with a very fast rise time.
The frequency response of the Television system is the main determinant of how well that transient can be reproduced, hence, resolution could be expressed in MHz

This was not commonly done during my 30 plus years in Broadcast Television, where resolution, frequency spectra, & system bandwidth  were treated as obviously related, but separate things.

The horizontal resolution of the old 405 line system is not that much worse than that of the later systems, because the slower horizontal scan time produces lower bandwidth electrical signals that do not require as much system bandwidth.

 
The following users thanked this post: helius, tooki


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf