Video Resolution
Edited postings by Brian Nestel & Scotty Henderson
 
 
A while ago I posted how resolution is determined on a CCD chip using just a horizontal component, its usually double the pixel size and the dynamic  
brightness/contrast determined by the word size of the D/A converter,  
so a chip with 12.5 micron square pixels would basically have a 25 micron  
resolution which would translate into about 1000 lines per inch.   
That's basically  for the chip, but the resolution drops when the 
video signal is converted to analog, The question is why? If you applied 
a pure horizontal you could have no more resolution than half the lines in 
the raster size, but that is not the way analog tv resolution is measured, 
For commercial TV transmission a formula that uses the Aspect ratio, number of horizontal lines making the picture, the number of frames per second, a constant for commercial tv quality, all together = Bandwidth!  The 
bandwidth for transmitted tv is about 4mhz video bandwidth, this translates to 
about 200 lines per inch, if you notice there is a horizontal and vertical 
component in determining the bandwidth limitation for transmission, This will 
determine how the resolution target is made, if you look at the target 
when it is put up on the web you will see that the lines determining the  
resolution are not pure horizontal and vertical put are tapered at a  
specific angle that has both certain horizontal and vertical components, 
now since we are not transmitting a signal that has to conform to bandwidth 
limitations, the analog video bandwidth is higher so we get more 
resolution on our images, the limiting factor is the actual bandwidth 
of the camera itself, the same CCD can be in different cameras of 
different qualities having different resolutions. 
That's the difference between SVHS and VHS, bandwidth! all other 
things like horizontal lines and frame rate are the same. 

The resolution target above (some quality lost in conversion to .jpg) is 
from a PC23C, I took two images of the target, one direct from 
the snappy, and one that I recorded on a 9" tv/vcr, I could not 
find any differences in the image that was taken direct or the 
one that I played back from the tape and snapped. Surprise! they 
all come up around 400 line per inch, the picture above is 
the image that was taped. Also the 9" monitor showed the same 
which surprised me. 

This will explain why some of you are 
seeing better results than you expected, I have seen mentioned 
the fact that VHS is only good for 200 or so lines per inch, 
guess what, that is the minimum allowed specification, The 
maximum will be determined by the quality of the video bandwidth 
of the components and tape heads, and since much better components 
are showing up on the market you will see better resolution, 

Now I am not saying that this is going to be as good as HDTV 
because there will be limitations on analog as opposed to digital, 

I have another camera that has a much higher resolution and I am 
going to try it in the same setup later and will post the results.
[Brian Nestel]
 
 
FAQs on Video Resolution

What does TV line resolution actually mean in terms of recorders, monitors and cameras?

Resolution is probably the most misunderstood and abused term in video
and television. It needs to be defined depending on what you are
referring to. Like many other specifications in electronics, the various
pieces that contribute to, enhance or limit the resolution will
determine overall system resolution at the output. Another aspect that
needs to be understood is the difference between detail and resolution.

If you have a 625 line TV ( PAL standard ) does this mean you only have a resolution of 625/2 = ~312 resolution of "horizontal lines" ( one every other raster scan line )?
Is TV line resolution the same thing as "vertical line" resolution ?
What is the usual "vertical line" resolution of common TV sets ?
Is there an upper limit to "vertical line" resolution in "broadcast" transmissions?

NO. You have either a 525 NTSC raster or a 625 PAL raster. You do not
have 525 or 635 lines resolution. Imagine spraying a wall with paint
262.5 lines spaced apart and then filling in the other 262.5 in the next
1/60 sec. Now imagine that the TV tube phosphor coating you have just
raster scanned 525 times in 1/30 sec has a mask in front of it with
small holes and there are 750 vertical rows. This is typical of a modern
27" TV set that has a resolution of 750 lines. At least this is the way
I understand it. Almost all references are to vertical resolution.
Bandwidth determines the limits. Modern TV transmissions reach your home via cable TV at 330 lines in NTSC and this is referred by some as
"broadcast resolution". New standards for HDTV have higher resolution up
to 1280 lines progressive or interlaced with in between resolutions.

What constitutes a "monitor" ? 
If you have a >1000 TV line resolution "monitor", does this mean it can resolve more than 1000 "vertical lines" if you fed it the appropriate test signal?

A monitor is a CRT without a tuner. A TV is a CRT with a tuner. A tuner
allows one to pick up off air broadcasts via an antenna or directly via
cablevision. A monitor only has direct line level video inputs, whether
it is composite, S video, RGB, or component Betacam. Many people use the
term "monitor" to refer to any display device whether it has a tuner or
not. Computer displays are correctly called monitors -- we never call
them TV's. Yes, and there are such monitors, for example, made by Barco.

Does the ~600 TV line resolution quoted for the Astrovid 2000 (for example) simply refer to "vertical line" resolution?

Yes. However, compare this data for some older cameras -- but not out of
line with newer cameras.

1/2" ccd 574 h x 489 v
50 dB s/n in mono, res 420 h and 485 v
46 dB s/n in colour, res 360 h and 350 v

You can see that the vertical pixel count is essentially the same as
mono vertical resolution but is reduced by  the addition of colour.

Why do you have more vertical pixels on a chip than there are raster lines on a TV ?

As explained above with the paint example, the raster is just a sprayer
of image information at so many cycles per second. The resolution is set
by the device by masking the electron beam into coherent image areas or
pixels if you like. You've heard of the term dot pitch applied to
computer monitors? The finer the pitch the sharper the picture (more
points making up an image). While a TV tube doesn't turn pixels on and
off like a computer, the beam excites masked areas of the tube to
achieve a similar effect.

You can make a chip any resolution you want. Try 2kx2k or 4kx4k. The
secret in imaging is detail, Detail is achieved by having many points of
reference composing an image, just as in photography, a 4x5 negative has
more  grains of silver representing an area than a 35 mm negative,
assuming image to subject ration is the same. In video detail and
resolution tend to go hand in glove so that a hi-res camera has more
detail. It is well proven in all fields of imaging that acquisition data
needs to be of the highest degree so that normal means of media give a
good representation of the original. Movies shot in 35 mm look great
even on VHS as do HDTV converted to VHS compared to your home VHS or Zumm. That is why for years TV news professionals used Betacam 3-tube
and later 3 ccd cameras costing $ 50,000 apiece. Not only have these now
dropped a lot, but the advent of digital camcorders has had a major
impact on the quality achievable. I can shoot 3.3:1 digital-S on a
$17,000 JVC 850 line 3-ccd rivaling 2:1 digital Betacam at 3 times the
price. Even consumer digital camcorders can achieve 500 lines and
remarkable detail on 3 ccd models for under $6,000. (All prices Canadian
value)

There are still b&w security cameras that have less TV lines than TV
scanning. 330 lines is the basic standard of many cameras in the economy
market.

What does VHS/sVHS do in the recording of a broadcast raster line that reduces the resolution so much ?

It doesn't, necessarily. Tape, or any medium storing an image will have
its own resolution. Digital forms of storage preserve any resolution you
have. VHS can only deliver 230 lines maximum whereas Svhs  delivers 400
line resolution. Record a cable TV program at 330 lines on both systems
and review. There is noticeable degradation and noise in VHS whereas the
Svhs is identical to the original broadcast because it can capture the
330 line quality and play it back exactly as 330 lines.

What equipment do you need to exploit the FULL potential of an Astrovid 2000 ( for example )?  ie what recording standard can record 600 TV line resolution ?  Is it only Betacam ?

Betacam actually has no better resolution than Svhs. The tape is
essentially the same. First generation Svhs versus Betacam with similar
or same type cameras indicates no visible difference. Betacam only has
an advantage over Svhs in the multiple generation department of 7
generations versus 5 for Svhs. Digital recording on a Sony Hi-8 Digital
camera would probably be the best at 500 lines or so. Direct computer
capture will produce best results at 600 lines.
.

.
I've tried to keep this simple. The main point is that I've worked with
all this and proven that, for example, the quality of computer capture
on a 514x514 display such as an older Matrox varies significantly
depending whether you use a 400 lines, 850 line, or 2K camera. The
imaging board can take all the resolution you can throw at it proving my
statement that the input device (camera) is paramount to highest quality
imaging.

Cameras like the PC23 are fine for fun and those who don't have any
budget (and do a very fine job) but it should be obvious by now that
serious work requires the highest quality imager you can afford. The
only thing that will attenuate results will be the optics in front of
it. Coke bottles won't help a KAF400 camera whereas a Questar will.
Lastly the imaging medium will set the final resolution. Drop 8mm and
VHS. Hi-8 and Svhs are much better, digital-8 even better again, and
finally computer is best if you can get decent seeing long enough get a
good series of captures.  [Scotty Henderson]