Peter C.
Veteran
I can see what you did. I think the best resolutions are made on New Years Eve.
Have I been wrong this whole time about resolution?
- Thread starter roxics
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roxics
Veteran
I was just using the analogy to say it's like blowing up an image and making it softer in the process. The 320x240 I used was just an example. I wasn't specifically relating those dimension to the analog world.
This part confuses. Is that a typo? Isn't horizontal resolution and picture width the same?
The horizontal resolution is the vertical lines running up and down that span the width of the 4:3 picture. Like columns stood left to right of each other. Correct?
https://www.dvxuser.com/filedata/fetch?photoid=5681356
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paulears
Veteran
not at all - just different uses of terms - so we have 'horizontal resolution' as in the capability to go from black to white detectably in a single horizontal line - with the digital square and rectangular pixels, and 'horizontal resolution' of each horizontal line from it's vertical neighbour. This is getting more confusing by the second. I do agree though that we normally assume vertical resolution of each horizontal line - but the test charts are clever things - each component designed for a specific purpose. By the way, you were right earlier - you do simply zoom in to these, or bring the camera closer until the corner marks match your display edges. In the US did you have test cards, transmitted out of hours to allow you to set the brightness and colour correctly and check things like circles being circles, not eclipses? Here's an old BBC 1 version
Attachments
Analog had various Improved Definition TV's and stand-along processors that digitally filled in the gaps. I mentioned the old Yves Faroudja processors that were present on the very high end projectors back in the late 80's and the 90's, while the 1989 $5,000 Sony IDTV looked OK for a frame with stationaryimages and horribly with anything moving. By the mid-2000's, I was able to purchase a 27" Advent IDTV for $240. It lasted a decade and looked almost as good as an HDTV.
roxics
Veteran
i don’t know. I didn’t work in tv back then. The most I’ve ever done with tv is shot and edited a few tv spots for clients. I didn’t start working in video professionally until the era of DV, around the time HDV hit the marketI. But I grew up with analog video in the 80s and 90s and made movies with my friends on VHS and Video 8 cameras back then.
I used to edit those movies with just the camera and a VCR. No edit controller or anything fancy. I couldn’t afford them back then.
I’m interested in the technical aspects of these things as purely a hobby and out of nostalgia. So I’m kind of just trying to fill in the gaps of knowledge I had back then, partly because I never got to work with these older formats and tools professionally back then but really wanted to. But also because I’m a fan of alternate history ideas. The “what if” scenarios. Which is why I ask some obscure questions sometimes. Like if a purely analog progressive scan video is possible. Those are always better played out if you know what is and isn’t actually possible in reality.
All of that said, I just want to clarified, when we say something is 400 lines of resolution, we’re talking about the horizontal resolution and not the vertical. The vertical is always 480 or 540 PAL. Or are we saying that it’s only resolving 400 lines out of a potential 480/540?
I feel like I still haven’t gotten a straight simple answer regarding this. Sorry. Although I really appreciate all the conversation and explanation.
combatentropy
Veteran
Yes. I remember them in the mid '90s mentioned in Videomaker magazine, but I never saw one in person. I think DLD was right, that they were called IDTVs (Improved Definition Televisions). I read that onlookers sometimes thought they were HDTVs, because of the improvement that progressive scanning brought. They were very rare, perhaps more instances on trade show floors than in people's living rooms. Soon, HDTVs took over, which brought both progressive scanning and higher resolution.
Why do you suspect that progressive scanning is incompatible with analog? The two features seem unrelated, in my mind.
Yes, 400 lines of horizontal resolution, per picture height. So to calculate the total number of pixels horizontally, mulltiply the resolution by the aspect ratio. So, 400 x 1.33 = 532.
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roxics
Veteran
I'm not sure. I know CRT TVs and analog broadcasts were interlaced. So I guess I just figured the nature of the technology had to be interlaced.
But then CRT computer monitors are not? Or are they and the tubes interlaced but the circuitry just accepts a progressive signal?
Is there a progressive analog recording format?
Ok so if I understand this right, then SVHS (420 lines) has a (roughly) digital equivalent of of 558 x 420 pixels?
Since 420 x 1.33 = 558.6
And that 420 lines is out of a potential technical maximum of 480 lines for NTSC.
Am I finally understanding this correctly?
In 1990, Sony had a 43" CRT with Improved Definition. Yes, a 43" CRT. It weighed a ton. Literally (OK, not quite but it was heavy). It came out about two years after the 27" and the picture was pretty good. The company where I was working only had a model on the floor of their Beverly Hills adjacent location. The set cost $35,000, twice the price of an average car. Allegedly, some rich celebs bought one or two.
https://www.latimes.com/archives/la-xpm-1990-04-08-tv-1907-story.html
https://www.latimes.com/archives/la-xpm-1990-04-08-tv-1907-story.html
combatentropy
Veteran
Interlacement was entirely to reduce flicker. Cathode ray tubes, if progressive, would have had noticeable flicker.
Not that I know of.
No, 558 x 480.
NTSC video always had 525 horizontal scan lines. That was the standard. As you know, some of them were not used for picture but sync and maybe overscan, so you wind up with about 480 visible on most TV sets (I think 483 or 486 to be exact?). That's the vertical resolution.
Among NTSC formats (VHS, S-VHS, Video 8, Hi-8) the only variation was the horizontal resolution. They always had 525 scan lines, which again was about 480 visible So the horizontal resolution was the only thing that differed.
So VHS and Video 8 were about 320 x 480. And S-VHS and Hi8 were about 560 x 480.
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roxics
Veteran
Interesting. So why do people even bother saying 420 lines for S-VHS or 240 lines for VHS if you always have to multiply that by 1.33 to get the actual horizontal resolution and the default for vertical is always 480-6 (visible)? Why not just say S-VHS is 560 lines and VHS is 320 lines?
[EDIT] Nevermind. I just assumed a default 4:3 ratio for every TV. I didn't realize they were creating a measurement that was aspect ratio independent. In which case I understand now why it's just 240 or 420.
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paulears
Veteran
We've answered all these questions over and over now, and we're just covering old ground with little extra bits.
You really cannot compare old and new. Interlaced pictures were also necessary because of phosphor spot decay - the odd or even frame was still glowing as the next frame was painted in the gaps.
The horizontal and vertical resolution is totally different. If you have 525 lines in America, the first thing was that some were off the screen anyway. The TV might have 525 lines, and the scan rate is fixed and we know how many are capable of being seen. So we might be able to say that we have 257 horizontal lines at any one time. Differences between varying quality televisions is going to give varying quality pictures. How wide each of the scan lines is, how sharp the focus is, is the overlay of even and odd frames totally different or a slight overlap? The video recorders with their 240 line resolution is nothing to do with the 257 horizontal lines we're talking about here. If the video can do 240, then that measurement is sort of progressive, as a measurement, but as we've said test charts generally are measuring the frequency response of the chain, buy measuring the capability of a black to white to black vertical grid - a square wave, the scan trace moving horizontally. The little squares of vertical black lines on a white background let you assess the frequency response from about 1.5MHz to 5.5MHz.
The bit about aspect ratios is to do with the frequency response. The distance the scan has to travel alters the ability to display the square wave - more divisions of the same size across the screen. This is not the same as the discussion about 240 vs 400 lines - both of those are not even linked to the PAL or NTSC system, which have different numbers of lines. Two different specifications, depending on what you are talking about - resolution in lines, limited by maximum frequency response, and screen display lines, set by the TV system format
You really cannot compare old and new. Interlaced pictures were also necessary because of phosphor spot decay - the odd or even frame was still glowing as the next frame was painted in the gaps.
The horizontal and vertical resolution is totally different. If you have 525 lines in America, the first thing was that some were off the screen anyway. The TV might have 525 lines, and the scan rate is fixed and we know how many are capable of being seen. So we might be able to say that we have 257 horizontal lines at any one time. Differences between varying quality televisions is going to give varying quality pictures. How wide each of the scan lines is, how sharp the focus is, is the overlay of even and odd frames totally different or a slight overlap? The video recorders with their 240 line resolution is nothing to do with the 257 horizontal lines we're talking about here. If the video can do 240, then that measurement is sort of progressive, as a measurement, but as we've said test charts generally are measuring the frequency response of the chain, buy measuring the capability of a black to white to black vertical grid - a square wave, the scan trace moving horizontally. The little squares of vertical black lines on a white background let you assess the frequency response from about 1.5MHz to 5.5MHz.
The bit about aspect ratios is to do with the frequency response. The distance the scan has to travel alters the ability to display the square wave - more divisions of the same size across the screen. This is not the same as the discussion about 240 vs 400 lines - both of those are not even linked to the PAL or NTSC system, which have different numbers of lines. Two different specifications, depending on what you are talking about - resolution in lines, limited by maximum frequency response, and screen display lines, set by the TV system format
roxics
Veteran
For some reason it wasn't clicking with me before. But after the last time combatentropy explained it, I get it now.
The way I used to think of it was that we were measuring 240 vertical lines (VHS) inside a 480 vertical line (NTSC) system standard. As in, not resolving the full 480 because VHS just wasn't good enough to do that. But now I understand that number is always referring to horizontal resolution and vertical resolution is always fixed at 480 lines.
That said, I understand that different equipment performs differently and that some cameras and televisions may not be able to meet that spec. In the same way that a poor quality lens may not resolve the full resolution of a sensor. As just an example.
I just wanted to understand what the measurement was referring to when people said VHS is 240 lines or S-VHS is 420 lines, etc. Now I know it's horizontal lines per picture height.
As a result I also now understand where the resolution 320x480 comes from. I have seen people refer to it multiple times for VHS and always thought it was wrong. I always thought that VHS being 240 lines meant the resolution should be 320x240, with the 240 referring to the vertical height. But now I get it.
That said, I still think it's an odd resolution as 320 horizontal is less than 480 vertical so you would think you would end up with a squished looking picture, but I guess since we're in the analog world here, those 320 lines just get stretched over the width without any issue. Despite there being more vertical resolution.
combatentropy
Veteran
You're right. It is weird.
However, Wikipedia corroborates our testimony:
"The horizontal resolution is 240 lines per picture height, or about 320 lines across a scan line, and the vertical resolution (the number of scan lines) is the same as the respective analog TV standard (576 for PAL or 486 for NTSC; usually, somewhat fewer scan lines are actually visible due to overscan)" --- VHS
"a horizontal resolution of 420 vertical lines per picture height" --- S-VHS
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This topic is becoming a rabbit hole. Some articles seem to say that the horizontal resolution was not only per picture height but took into account the Kell Factor. Therefore the total number of horizontal pixels for VHS may have been 456. And that would mean that Super VHS was nearly 800, more than DVD!
However, Wikipedia corroborates our testimony:
"The horizontal resolution is 240 lines per picture height, or about 320 lines across a scan line, and the vertical resolution (the number of scan lines) is the same as the respective analog TV standard (576 for PAL or 486 for NTSC; usually, somewhat fewer scan lines are actually visible due to overscan)" --- VHS
"a horizontal resolution of 420 vertical lines per picture height" --- S-VHS
---
This topic is becoming a rabbit hole. Some articles seem to say that the horizontal resolution was not only per picture height but took into account the Kell Factor. Therefore the total number of horizontal pixels for VHS may have been 456. And that would mean that Super VHS was nearly 800, more than DVD!
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Analog CRT displays may not have discrete fixed pixels like digital displays, but they have finely focused electron beam dots. On color displays the "pixel" resolution was determined by the size of the phosphor dot mask scanned by the electron beams. Those occupied a fixed space just like a digital pixel, but the luminance value of any particular dot was continuously variable.
Interlacing was created to limit the transmission bandwidth of video to fit within a 6 MHz bandwidth RF channel. When NTSC color became standard, YUV encoding with subsampled chroma kept color transmission within the same 6MHz limit.
Interlacing was created to limit the transmission bandwidth of video to fit within a 6 MHz bandwidth RF channel. When NTSC color became standard, YUV encoding with subsampled chroma kept color transmission within the same 6MHz limit.
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paulears
Veteran
Aha! Lets not stray into the NTSC Vs PAL area of TV as we'll never get to the end. Looking back, the whole thing was quite confusing. Just remember the test cards, with their vertical black and white bars. That was pretty much the only thing that mattered when you were talking about resolution. The UK and the US systems had different numbers of lines, and different colour systems, but we were all glued to those frequency limiting bars. They were pretty good really - because drops in quality anywhere in the transmission chain, right from camera to TV screen would impact those resolution bars. The differences between 3 dots, or 3 little slots, or Trinitrons could be measured by those bars, but the visual differences between them were quite obvious when you watched a picture.
Analog CRT computer monitors were progressive scan. Interlace was just a way to maintain resolution while reducing over the air transmission bandwidth of NTSC color TV to match the 6MHZ RF channel bandwidth of progressive scanned black and white. 6MHz RF channels are still used today. With ATSC compressed digital signals we can fit one 1080i 59.94HD interlaced signal or one 720p 29,97 progressive signal plus two SD resolution signals into the same channel bandwidth. Now that can extend to 29.97 progressive scan UHD as the only signal.
Kell factor is roughly the analog equivalent of Nyquist factor regarding the capability to optically resolve an image without visible artifacts. In practice a 1080HD image will resolve between 600 and 850 lines per picture height without noticeable aliasing and moire artifacts. An SD signal between 240 and 350 LPPH.
We used to run similar LPPH resolution charts setting up film projectors in theaters. The best resolution for Academy format 4-perf 35mm test prints I ever saw was around 800 LPPH, limited by jitter and gate weave of the film as it moved through the projector.
Analog SD programs that were originally shot on videotape have not held up well. Most look pretty bad, which is why they are seldom rerun. Those that were shot on S16mm film or 35mm film still look very good with modern restoration.
roxics
Veteran
I knew the VGA connector (or whatever it's actually called) is analog, just wasn't sure if the display was interlaced. I didn't think it was, but I wasn't sure.
Also I had no idea B&W TV signals were progressive. That's really cool.
I had heard that before. That film prints were somewhere around the digital equivalent of 720-1080.
It amazes me how good modern upscaling can look for SD to HD content that originally was shot on film. Where they are not doing a new film scan, just upscaling the video tape. Really goes to show how important that front end capture is.
In fact I used to say years ago I would be fine with a camera that recorded onto VHS, if the front end gave me a picture that looked like 35mm film.