HIGH RES WITH LOW RES EQUIPMENT? WHAT HAPPEANS?

[jisaac 0]

I know there has been several post about resolution mismatch.

 

What happeans when you have a high res camera but a low res monitor.

Or

Low Res camera with a high res monitor.

 

And several other related questions. Well I found this. Its an article by charlie price. Thought it might be helpful

 

 

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Dear Charlie,

 

Is there an advantage of using a high resolution (570 lines) camera with a time lapse recorder that has a resolution of 300 lines?. In other words, would the recorded image from a 570 line camera be higher quality than a 380 line camera? How does the video recorder interpolate or "compress?" the higher res image into a lower res image? Is it similar to audio where a higher quality source makes a better recording than a lower quality source, even though the limitation of the recording device may be less than the higher quality source?

 

Thanks for your help. Just sign me "Losing lines in MO"

 

Dear lines

 

After all the hub-bub that is made about resolution, what is this phenomenon that we keep telling you is so important to the video image? More importantly, what is the real affect of high or low resolution images in our security applications? I mean, we all know, or have heard, that you should use a higher resolution camera outside, or for long shots, but why? In the end, does it really matter what style of camera we use? Actually it does, but not necessarily for the reasons that you have been thinking or lead to believe.

 

First let us describe and define resolution. There are several ways to measure the resolution of an image. You can use the actual number of horizontal lines used to manufacture the image (horizontal resolution), pixel resolution, or vertical resolution. To understand any of the different resolutions, we must first go back to the basics. First, how is the video image recreated on the monitor screen? Don't run, this sounds highly technical, but we can break it down to simple terms. To give an image the illusion of motion, we flash a series of fixed pictures on the screen at a rate that is faster than the human eye can detect. Each fixed scene is incremented slightly farther ahead in the action than the one before it. When we put the image on the screen, we don't just flash up a picture, we paint the image one line at a time. This line of video information is painted on the screen from the left side of the monitor to the right and is referred to as a horizontal scan line. We first go down the entire screen painting only the odd lines, then we repeat the process filling in the even lines of information. This process is referred to as two to one (2/1) interface. In the end, we create a total of sixty (60) half images (fields) or thirty (30) frames per second (US) or fifty (50) fields / twenty five (25) frames in countries using 50 Hz power. The total sum of these lines create what we refer to as the vertical resolution of the image. I realize that this seems somewhat confusing, but vertical line resolution refers to the total number of horizontal lines. This is because we are counting the individual lines of information from top to bottom or vertically. Leave it to an engineer to make life confusing.

 

In the US, Canada and many other parts of the world, we work under NTSC (National Television Standards Committee) standards which fixes the video image at sixty (60) fields per second and 525 vertical line resolution (525/60). In Western Europe, Australia, parts of Africa, and the Middle East, they work with PAL (Phase Alternating Line) format which fixes the video image at fifty (50) fields per second and 625 vertical line resolution (50/625).

 

But how do we paint an image on the screen? What magic could possibly exist that gives us the ability to make an image? It's really very simple. If you have ever pushed your face close enough to a monitor or television screen, you have seen rows of independent bright spots. These little spots are referred to as pixel points. In the end, a video or television image is nothing more than a collection of variously shaded pixel points. The total sum of these pixel points on the screen is referred to as the Pixel resolution. The total number of vertical columns of the pixel points (counted from side to side) is referred to as the Horizontal resolution. This is because we are counting from left to right or horizontally. Again, just a little confusing, but par for the course. The horizontal resolution is determined first by the camera, second by the transmission method, thirdly by the weakest link in your video system.

 

The combination of vertical and horizontal lines create an overall format resolution that will determine the quality of the image. Since the vertical resolution is fixed at either 525 lines (NTSC) or 625 lines (PAL), we depend upon the horizontal resolution to determine or define our image quality. Imagine the entire video image on the screen as nothing more than a drawing made on a grid paper. The smaller the squares, the more defined the lines in your drawing can be. Consequently, the more lines used to make the grid, the smaller the squares.

 

Now, to the heart of the matter. The first lesson to remember is that the overall quality or resolution of your image will only be as good as the weakest link in your video system. Consequently, there is a lot of money being spent on high resolution equipment, but the results are coming out equivalent to lower resolution images. For example; the average nine inch (9") black and white video monitor will reproduce, up to, six hundred lines of horizontal resolution. As a quick note, the average television only produces three hundred and twenty five lines of horizontal resolution, which is why a video monitor almost always looks better than a television. Now, let's say that we have a camera that produces an image with eight hundred lines of horizontal resolution. Will the monitor make the eight hundred line image or will it drop off two hundred lines of resolution somewhere and reproduce an image of six hundred line quality? Answer, drop off two hundred lines of resolution and reproduce an image of six hundred line quality. In retrospect, what if we had a camera that manufactured an image of three hundred lines of horizontal resolution. Would the monitor reproduce at six hundred lines? Answer, no. In the end, the monitor is an idiot box with no ability to recreate what wasn't there in the first place. The monitor however, is seldom the problem. Consider that the average video recorder, used in today's surveillance video systems, only has a reproduction capability of an average of three hundred and twenty five (325) to four hundred and eighty (480) lines of horizontal resolution in the playback mode. "But, my monitor has six hundred (600) line capability and I bought a special camera, for a small fortune, that has eight hundred (800) line horizontal resolution!" Oh well, now you know why your video playback is never as good as the image on the screen. Figures, doesn't it. You thought that you had a problem with your video recorder and have just come to find out that you really do. You spent too much money on a camera that the VCR cannot emulate.

 

You have however, also just learned another key reason for using professional, industrial video recorders instead of the two or three hundred dollar consumer units that you buy at the store. It's really simple if you know just one more thing and that is that your television only has three hundred twenty five (325) line horizontal resolution. Therefore consumer recorders are not going to be built at such a level as to produce more resolution than the television can.

 

One place where we need to use higher resolution cameras is outside. This is because the majority of our outside cameras are using longer than usual lenses (more telephoto) and are usually on longer cable runs. Since we can loose resolution or quality of image by looking through telephoto lenses, and we can loose resolution on long cable runs, we prefer to stick with higher resolution cameras up front. Think about it. If the image is going to loose resolution, before it hits the CCD (Charged Coupled Devise), or because of the cable run, wouldn't it make sense to have as much of this stuff as possible? Absolutely! But this isn't the sole or even the most important reason for using the high resolution cameras.

 

OK it's time to get to the meat of the situation. Assume that our position is one of security and that we need to identify various objects or individuals on a video screen. Also assume that we will be doing this from two perspectives. The first perspective is while looking at the screen on the monitor with a direct feed from the camera and the second is during the playback of the image off of the video recorder. For the first example, I will use a camera with a horizontal resolution of six hundred lines (a really, really good one). I am looking at a six foot man and he fills my screen from top to bottom, head to feet. So we can say that our image resolution is about five hundred and seventy (570) lines (assuming a 5% lose due to cable and lens).

 

This is good, however, what is the amount of resolution that we can use for the identification of the person from a facial perspective? Five hundred and seventy lines? No, in fact the average human head (face) takes up only one fifth (1/5) of the overall body. Therefore the true resolution of the mans face is only one fifth of five hundred and seventy lines or roughly, one hundred and fifteen (115) lines. This is still a huge amount of video information and so we will be able to make a solid identification of the individual (provided that lighting and angle of view are adequate). On the backside however, let's say that we are now looking at the play back of our time-lapse video recorder. We have the same man, same scene, same amount of scale and size. The difference here however is that our recorder only has three hundred and twenty five (325) lines of resolution at play back. Now what is the true resolution of the man's face? One fifth (1/5) of three hundred and twenty five or about sixty five (65) line resolution. Still very good and easy to identify, so we're OK.

 

For the second look, let's drop the man's overall appearance in the scene from taking up the whole screen into a little more realistic attitude. Let's make the man one inch (1") tall on an eleven inch screen (11")(as measured diagonally). This would mean that his whole body takes up about one sixth (1/6) of the overall screen. What is the overall resolution of the man this time (assuming the same scenario as described above). For his overall body, we would take one sixth of five hundred and seventy (570) lines of resolution or we would say that his body had ninety five (95) line resolution. His face would be one fifth (1/5) of that or nineteen (19) lines of resolution. Getting low, but we should still be able to identify this individual. Now let's go to the playback at three hundred and twenty five line resolution and take another look. Our first calculation says that the man's body uses one sixth of the overall scene for a total of fifty four (54) lines of resolution. His face is one fifth (1/5) of that or roughly ten (10) lines of resolution. Probably still enough for identification purposes, but certainly pushing the envelope. On the other hand, what if we needed to identify something about this man in specific to make our case.... say his shoes. His feet would represent about six inches of overall identifiable surface area in real life. If we reduce this to screen size, we could say that the top surface area of his shoes (assuming we have an elevated angle of view looking down at the man) would represent about one third (1/3) of the same amount of area that his face did. Therefore, we would have roughly three and one half (3.5) lines of resolution, on playback to use for shoe identification. It would not be enough to make a case.

 

At this point, you may be saying that I am going too far and that a man's shoes is not a good basis for an example. I would wager that you make this statement based upon the lack of believe that such is evidence. However, think back to O.J. Simpson... were not his shoes of some question because of the bloody trail? Several weeks ago, I was involved with an FBI case where they were trying to prove guilt of a man based upon a video tape playback and the nature of his shoes in particular. This man had entered into a large retail store, was dressed in a black coat, black pants, black pullover stocking cap (not that unlikely in Iowa in the winter) and black shoes with some sort of white markings on the top. Turned out to be white doves on top of his shoes and they were the ones he was arrested in. The problem came in the playback of the video that captured his image during the robbery. When I first saw the image, it was played back via a consumer recorder on a color television. His shoes were defined by about two lines of resolution and the doves appeared to be something related to what a dove might leave on your shoulder. Played back on a proper industrial recorder and with a black and white monitor however, his shoes in fact had a full six lines of resolution and the doves stood out like an accusation.

 

In the end, resolution of an image is much more than just how many lines we use to paint the screen. It relates to the overall screen, relative size of the object of identification, and the type of equipment that the image is recorded or even played back on. This is what resolution really means to you in the field. Therefore when you design your systems, keep in mind that the size of an object in perspective to the overall size of the scene is also relative to how many lines of horizontal resolution will be available to describe the object. The smaller the object of identification, the higher the camera resolution will need to be. The larger, less defined the object of view, the lower the overall resolution can be. Keep in mind however, that it is the weakest link of your system (usually the recorder playback) that will be the most important thing in the end.

[kelvin 0]

for HR camera with low-res equitment. result will be low res.

 

low res camera with HR equitment you still get low res image.

 

you have to fit all your camera and equitment with same standard. same as theory like upgrade a car, exp. you cant have a car with 300horse power but using a standard brake.

[kensplace 0]

And dont forget things like multiplexers, quads, humbugs, cable, connectors, baluns etc.

 

I can look at a pic through one multiplexer, and it shows the picture more to 'the left' than just vieiwing it direct would, also plexers that store frames internally can have low res too. Course manu's dont always tell you things like this......

 

As far as that instance goes about the man with the doves on his shoes, I dont really think the problem was the playback device, I think it was recorded wrong in the first place, if they wanted to id someone they should have a close up camera on the entry/exits, and another for following people around, at the least (ideally with p/t/z).

A bad camera/lens setup is not going to be improved much by using a better recorder, even a cheap vhs recorder will be able to record a well captured image, if the system is designed correctly to start with..... But a better recorder is always better in the long run, why throw away most of what is captured by using a cheap (or in many cases not cheap) dvr.

 

Even geovision cards, although I have not used one, seem to record at a lower resolution that what a decent camera can produce, which means some of that nice image detail is being lost - and thats with a industry standard card...

[Cooperman 0]

Hi jisaacmagee,

 

I've just read through this post again for the third time, and quite honestly, I need a stiff drink

 

What should be a fairly simple concept to explain in perhaps a dozen lines, has been given what can best be described as a thoroughly confusing, and in places quite inaccurate and misleading work over, which had me scratching my head trying to work out what was being explained, so goodness knows what some of the less experienced guys would have made of it

 

No disrespect intended J., but with your broad practical experience, and given some of your previous excellent postings, I'm sure you could have explained this concept far better, and in a way that could be easily understood by all.

 

I'm not going to go through this epic piece line by line, but for what it's worth, here are just a few of the points which perhaps need clarifying:-

 

1) Two fields combined into a single frame are described as being 2:1 interlace... not interface.

2) You don't just use higher resolution cameras outside - the golden rule is to use the highest resolution camera that can be afforded, whatever the application.

3) Suggesting that the maximum number of lines in the scanning system ( i.e. 525 EIAJ / NTSC & 625 CCIR / PAL / SECAM ) equates to vertical resolution is patently wrong. The scanning system will only limit the maximum available vertical resolution, and in most cases, the average camera VR is nearer to 400 lines.

4) I'm suddenly getting a serious case of deja vu; I'm sure we've been through this before

5) Image resolution, or to be more accurate camera resolutions, are often subject to many types of degradation which have absolutely nothing to do with the principles of system engineering; for example, smoke in bars, heavy rain, fog, dirt on housing windows etc.

6) In practice, the resolution chain is only as strong as its weakest link, and based on the sequence in the article, it should be ... camera, lens, illumination, transmission, recorder, monitor, and whatever else you want to throw in to the circuit. Actually, come to think of it, illumination was never even mentioned, and low light causing camera AGC circuits to work hard, with increased noise on the image, is a sure fire recipe for reducing resolution.

7) Suggesting that "we can loose resolution or quality of image using longer than usual lenses" is quite misleading.

In general terms, telephoto lenses are far better corrected optically than standard or wide angles, so in most cases, are capable of much better resolutions than their shorter cousins. This is particularly true of longer lenses, which are normally designed for use on larger formats. It is also true however, that where longer lenses are used to observe over greater distances, then atmospheric conditions can serve to reduce the perceived quality and resolution.

 

I'm way too tired tonight to cope with much more, but suffice to say, I agree with much that kensplace has already said.

 

If you capture a cracking good image on an average camera, it will always beat a poorly configured high resolution camera. Personally, I never use anything but high res. for my own work, but that's not to say that I don't on occassions have to get the best out of some clients poorly designed systems, when they're not prepared to spend any serious money on improving it.

 

Life is way too short to be making things overly complicated, and difficult for many people to understand

Maybe I'm just getting a bit picky as I get older, so apologies if this sounds a bit like a rant, but sometimes keeping things simple is far more worthy of respect, than when some experts just simply try too hard to prove how clever they are.

[kensplace 0]

If I had not tried long range zoom lenses, I may have been put of by that explanation, saying quality can be lost, but as you say, it usually not the lens that causes the problem.

 

I use a 7.5 to 75mm zoom (also have a 12 to 120, and even a 25 (or thereabouts, cant be bothered to dig it out from the cupboard) to 350mm lens)

 

The 7.5 to 75mm is brilliant, wide enough at one end to see a wide overview, and powerful enough to zoom in to distant faces/plates if need be, lovely lens (would hate to buy em new though, pricey!)

 

The 12 to 120 is good, but a tadge trickier to control, but great results non-the-less, I just prefer the 7.5 to 75 as it has a better wide angle.

 

The 350mm monster (which is about a foot long, and weighs a LOT) is the one that I rarely use, mainly due to its size (as the cam is indoors) and the fact that its just sooo powerful, its overkill for my needs. If I wanted to monitor a area from a block of flats then it would be great, but catching local kids smashing windows etc does not need such a beast

 

 

All the zoom lenses give brilliant results (as far as I know, cant compare them to a modern dome cam, not got one of those to play with yet....) though, even at max zoom, probably because of the size and quality of the optics. As you said, the atmosphere does come into play, but I only notice it a bit on the 350mm, the others dont seem affected, and I can still see fine at night through the other zoom lenses when they are on a decent cam.

[jisaac 0]

your right he did get into his own little world there for a little bit before bouncing in and out of reality. And I probably could have shortened it. But the thing that was in favor of cut and pasting the article was the fact that it was already typed out and I was out of my adderall (add medicine). And if I made a post without my adderall in me you would really be confused!!!