CameraGimp

Bear with me, I've just come back from the pub so I may read this different in the morning. Are you simply saying viewing something head on it is brighter than if you light it at an angle? Which makes sense but makes me go well yes. However I can see how that causes problems to cameras because their exposure circuits can't cope with low light and bright spots. I don't work in cctv though, I just have a head full of it. Perhaps cynically I doubt many people would make a low cost IR illuminator when they can market expensive ones and make people think IR is something special when in fact it is just a light. Heck, why are high end 1/2" IR exviews so expensive when they are identical to a cheap monochrome except they use a $5 more expensive CCD which is pin for pin identical to the cheap one? Marketing maybe?

Can anyone explain why having the camera and the light source close together is a bad thing. I'm happy to accept it as true if experience says so but I'd like to understand the reason for it. Here is how my head sees it and it may well be wrong but where I don't know. Everything we see (apart from light sources) is reflected light and all light we see comes straight at us cos light doesn't bend. Now to see something the light has to hit us in the eye. If it whizzed past our ears we wouldn't see it, right? So why would it matter what angle the light was reflected from? All light we see always comes straight from the object to the eye. Headlamps on cars and torches work ok and they are straight out/straight back. Why is this any different?

I can't say I agree with a lot of that. An aspherical lens allows you to open to a wide fstop without it going soft focus it has nothing to do with IR. Perhaps you mean an IR corrected lens? Look into chromatic aberration and remember IR is just like visible light but past red to see how they work. An IR cut filter stops IR so having one on an IR camera kind of defeats the main reason for having an IR camera. Perhaps your thinking about a true day/night camera? That would require an IR cut filter. You have to spend to get clear images with IR. Simply not true. You just need to know what you are doing. The most expensive IR camera has nothing in it that will give you sharper pictures than the cheapest IR (lens excluded). Or if there is I'd love to hear what it is. Here is what I think is happening. The camera is viewing a dark scene, the majority of what it is viewing is not well lit. When your wife walks close to the camera she is being hit by a lot of strong light (forget it's IR just imagine she is standing in front of a headlight). The camera sees a mainly dark scene plus a brightly lit area (your wife). This brightly lit area is not enough to really influence the cameras exposure circuit so it continues applying gain to boost the dark areas and a side effect is it allows your wife to white out. Cameras are dumb and they don't know that your want to see your wife, they have to make a guess and they guess you'd prefer to see the whole scene and allow some areas to be too dark and some areas to white out. We have features like BLC and peak/average to try and get round this but they aren't perfect. To test my theory put some things in the scene that will reflect more IR and make the camera apply less gain. If it works the camera won't clip your wife as much. The down side is the dark areas in the scene will be darker.

Here are a list of common functions you might get on a four dipswitch camera and how to spot them. AGC - Cap the lens, flick the switches and look for one that makes the picture noisy, when off it won't be. Sync, Linelock/Internal. Power the camera with AC, flick the switch and if the picture rolls for a second chances are it's switching between line lock and crystal lock. Can confirm by powering with DC and then the switch will have no effect. As previous poster said, it's not used nowadays unless switching with an analogue switch. Gamma. It will change the contrast. EI on/off. Point the camera at bright light with a manual iris lens. Open the iris so the camera overexposes. If it doesn't EI is on in which case flick switches until it does over expose. If it does white out flick switches until it doesn't! BLC on/off. Going to be hard to spot but with ei on and the camera viewing a bright scene flick the switches and see if one changes the exposure slightly. That'll probably be BLC. AI and AI-AMP. One will be DC lens and the other video iris.

Hi, What do you mean by dome infrared? Just to clarify. Are these day/night cameras that are going mono at the wrong time or colour cameras that are going mono. I don't suppose you can connect an oscilloscope and do you know what a colour burst is? Perhaps the colour burst is being degraded for some reason. If the colour loss is regular can you unhook from the dvr and go straight into a monitor and check if it still goes mono. I wouldn't have expected baluns to have problems over such sort distances but weirder things have happened.

No I am not. The cheapest CCD camera has an electronic iris that is more than enough for daylight with or without an IR filter. You need to look at the effects of removing an IR filter on greyscale reproduction because I can assure you IR sensitivity does not effect exposure in the way you think. Ok there is more light falling on an imager when you remove the ir filter but the effect is no different from switching to a faster lens, the sun coming out from behind a cloud or someone turning lights on, the cameras auto exposure circuits will adjust and it can cope with sunlight without an filter. Electronic iris is proven and there are 1/2" IR exviews installed outside with manual iris lenses without exposure problems. I think you are getting over exposed confused with washed out. We know that an IR sensitive camera sees things differently to us or a colour camera, we know IR messes up colour but it messes up other things too. Look at the leaves on a tree with a colour camera and turn the colour off on your monitor. The leaves will go from dark green to dark grey. View those same leaves with a monochrome camera that can see IR and the leaves will look a lot paler. This isn't washed out because the camera can't cope. They are reflecting IR and that is how they look to something that can see IR. If a monochrome camera appears to have less contrast it is because the scene it is viewing has less contrast but it is not washed out because the IR is swamping the exposure circuit, it is coping as it should. If only we could see IR that is how it would look. Hope that makes sense.

HQ1 has nothing to do with low light performance. It is a DSP that gives better resolution (520TVL). If you want to compare sensitivity you need to find out what CCD the HQ1 camera uses.

It's not possible to say. SuperHAD is a type of CCD whereas HQ1 is a DSP not a CCD so it is like comparing apples with oranges. Anyone that says HQ1 CCD (and many do) has it wrong. Cameras have a CCD and a DSP. The CCD is the chip that you know as the sensor, this bit captures the light and it is fair to say that Sony make the best ones (in general cctv anyway) and the DSP is the processor that does the rest. The bigger the CCD the better it is at low light, the sizes are 1/6, 1/4, 1/3 and 1/2" with 1/2" being the most sensitive. Sony make a number of ranges of CCD, SuperHAD, HyperHAD, ExviewHAD and a new one I don't know the name of. The sensitivity goes up as I've listed them. Now this is a bit of a sweeping statement but the CCD goes a long way to determining a cameras low light performance. So if you have two cameras from two reasonable manufacturers that use the same CCD then they will perform about the same. I'm sure that will cause some arguement but it's my opinion. Any way if you have one spec saying HyperHAD then you know the CCD in that camera (and it's an ok one) but if the other camera says HQ1 CCD then I think they have it wrong and HQ1 is the DSP that gives 520 TVL. It may use a HyperHAD ccd but then again it may not.

I think you may be falling foul of unclear or poor marketing and specifications. Firstly, SnR on its own is not a good indicator of sensitivity, so the camera with the best SnR may not be the most sensitive. Also I think that HQ1 is a DSP and not a CCD so you can't compare the two.

Sorry but exposure will not be affected by a filter. Pixels in a CCD gather charge. They do not know and cannot differentiate between white light, blue light, pink light, IR or anything else. If it puts a charge in the pixel that is all they care about. DSP's create colour as colour CCD's (which are exactly the same as mono CCD's except for this) have coloured filters over pixels and they calculate colours and brightness from these four pixels. IR light of any wavelength is just charge to a pixel. Any camera that will automatically adjust exposure will do this just as well for natural light as it will for IR light. So although a colour camera with a notch filter may be one f stop more sensitive than one with an IR cut it's exposure algorithm will operate exactly the same. The only exception is if the light levels are so high that the shutter speed or AI lens fstop cannot cope but that is very unlikely in any camera made in the last ten years. I fully accept the colour balance will be thrown out the window but not exposure. The camera will see a bright spot of IR light exactly as it would a bright spot of natural light and adjust for it. Again, how can a monochrome camera work otherwise. They use the same CCD except for the YMCK filters over the top but they do not over expose during the day. IR cut filters only affect colour balance and grey scale reproduction. The camera becomes more sensitive but the camera can cope with that in exactly the same way as it would if you put a better lens on it. Perhaps the issue is the poor greyscale reproduction? A camera that can see IR may show a dark object as light grey. It may look black to us but if it reflects IR it won't be black to a camera.

That's not right. The IR cut filter is needed to ensure correct colour reproduction. It has nothing to do with correct exposure unless you wanted to guarantee correct greyscale reproduction on objects that reflect IR. If an IR cut filter was needed to prevent over exposure how would any monochrome or IR sensitive cameras work in the day?

I know that with some (maybe all) DM units you can't just swap faulty drives and the units work. New drives need to be formatted (or some other magic) it a certain way before they will work. Here is a link to someone asking something similar. You may need different software. http://www.cctvforum.com/about7369-15.html

As the camera gives a colour picture it can't be a black and white camera and as it is IR sensitive at all light levels I would have thought the assumption that the camera doesn't have an IR cut filter is quite good. What is a digital day/night and how do they work?

Hi, I can't be 100% sure but I would guess that the camera uses chroma suppression triggered by AGC gain to go from colour to monochrome. From what you have said and tried out it seems to fit. So although your camera has a photocell, it only uses this to turn on the ir leds, it doesn't use it to switch the colour off. Most colour cameras slightly reduce the colour strength at low light (it gives a cleaner picture) and if I had to make a choice I would say that is how your camera goes to monochrome. It probably suppresses chroma totally. Some cameras suppress based on how much agc gain it is applying. The logic being if I'm applying 0db of gain it is bright, 10db it is getting darker, 20db darker still, etc. The settings in the camera firmware would be at this agc level start suppressing by this much. I don't know how to suggest you test this. You might be able to try turning AGC off. If your camera supports this you might stop the camera going into monochrome completely. Not much help if you want to force the camera into monochrome though.

Mmm. There an a few different flavours of day/night cameras. Good ones (or proper ones) will have a mechanism to move an ir filter across the ccd. It should be there during the day and away at night. The switch to monochrome isn't really necessary. Can you check if you have a moving IR filter. Point an ir tv remote at your camera with the tape on/off the sensor. If you see it/don't see it you have a moving filter. Ta

I can't say what's wrong but I can confirm that it shouldn't take 5 minutes to get a stable picture with that camera.

I would have thought the answer would depend on which country you live in.

No, it is one standard ptz camera with a plastic insert with four fake lenses moulded into it. The one real lens is the one you can see poking through the insert. As the real camera pans it turns the insert and it looks like four cameras or it disguises where the real camera is looking. There is only one camera in the housing

Yes, an IR pass stops everything below a wavelength but allows those above. I'm fairly sure this is how some anpr cameras operate. You remove all the useless parts of the image so the computer has less trouble finding the plate and you control the light level not the sun. Filters are available via the net or maybe try the glass fitted over old ir lamps, the ones that use filament bulbs. They stop visible light and pass ir.w

Here is how I would make a camera to capture number plates. Start with a fairly low cost monochrome camera that allows you to set fixed shutter speeds. Set the speed so you get sharp images of fast moving plates. Leave it at this speed. Don't use electronic iris, this ranges from 1/50 - 1/100,000s and you will get blurred images on the slow shutter speeds. Fit an IR pass filter (Note - this passes IR and is not the IR CUT filter as used on colour and day/night cameras). With this in place the camera will only see IR light. The camera won't be bothered by headlights as it won't see them. This will make the camera useless for everything but seeing number plates. Shine IR at your on coming cars. The IR will reflect off the plate and you will see it. You won't see the car, its headlights or the road just the plate.

Your question is too vague. What kind of lighting in the scene? What distance will the camera be from the subject? How will you control the ptz? Is size or cosmetics important? Internal or external Budget

Here is a guide to camera functions. It is a few years old now but it has information on everything except DNR and SENS UP. www.darkdata.co.uk/camera_lenses.pdf DNR - Digital Noise Reduction is a feature to reduce AGC noise. SENS UP also known as Slow Shutter or Digital Slow Shutter or Frame Intergration is a feature for low light. Usually a camera has a maximum exposure (shutter) of 1/50 or 1/60 second. Slow shutter extends this. Leaving your shutter open for 1/2 a second allows you to gather more light per picture however moving objects tend to blur. Everything that moves looks light the starship Enterprise going into warp. It is good for watching perimeter fences but not good for catching a face.

I'd say that your finger is being seen by the camera as a large bright object, so the camera isn't applying a lot of gain and so the number plate isn't clipped. In the scene without your finger the number plate is a smaller portion of the scene but the brightest part. The camera applies gain so you see the dark areas but allows the highlights to clip so you can't see the number plate. Try bringing the number plate closer. It'll probably do the same thing as your finger if you get it close enough.

I've never come across your camera but.. The motor will move the ir cut filter. Most likely it will be controlled by the camera based on light level. Line lock is a feature used to sync multiple cameras for use with analogue switches. It isn't used much nowadays. I'd suggest you set it to Internal or crystal or off. I not sure on this one but I'd expect the lens holder isn't available off the shelf.

Your comparison with photography is pretty accurate and the reason we'd use shutter over iris is usually cost. A fixed lens costs less than a motorised one. There are advantages to motorised lenses but they cost more. The big differences are the depth of field and smearing. In CCTV we want low light perfomance so if we use a fixed iris lens with shutter we will always set the iris wide open and as a consequence we end up with reduced depth of field. A motorised lens will give us more depth of field during the day. Smearing is less of a problem nowadays but CCD's can suffer under extreme bright light, light bleeds into the registers and you get vertical streaks. A motorised lens stops this. The blurring you refer to isn't usually an issue with either shutter or motorised lens as both will have the same max shutter exposure.