Confused about Lux ratings on brandname body cameras.

[photys 0]

I have a brandname camera that states 0.3lux @f1.2

(also up to 0.002lux using Sens-up but disregard that for this post)

An f0.95 lens.

AGC has options of off/low/medium/high

 

When I use AGC im very happy with its low light capabilities.

 

However, if I turn AGC off, it appears to be more like a 3 - 5 lux camera.

I pretty much have to hold a candle an inch from my face to get an image.

 

 

To my question......

If AGC is digital post processing, how can they say it is a 0.3lux camera?

Or is that 0.3 lux rating the best it can achieve using AGC only?

[CollinR 0]

All those numbers are basically BS, I'm not going to do the math but you can't directly relate that lux number back to 1 candlepower of light like you should.

 

I would assume .3 lux would be the maximum possible performance, so in your case AGC on. I'm pretty sure Sens-up is tied into the AGC as it too should use gain controls. Turning AGC off may well disable it too.

[photys 0]

Cheers CollinR,

I always appreciate when yourself and other knowledgeable members take the time to answer my mundane questions

Yes, your right, Sens-up is only available with AGC.

 

 

Ok, so in general, brandname company's sell their cameras by lux level at max gain?

But gain causes a deterioration of signal which demands yet another digital process which can blur an image (low pass filter or some signal noise reduction).

[rory 0]

Manufacturers will post all kinds of different specs, it can change from one to the next and one product to the next. The Lux level will simply be their rated lowest level the camera can achieve using the specified lens F Stop. It should say whether that is with AGC or not, but that depends on the manufacturer, they are all different.

 

So in your example, it claims 0.3 lux with an F:1.2 F Stop, however your lens is F:0.95 so it will go much lower than 0.3 lux, or at least it should, depends on the camera though, or moreso the chip. Ofcourse typically you can ignore the lux level specs anyway, as like Colin said it is typically BS.

 

I wont even discuss SensUp, as thats just a digital Gimic.

Im guessing its a Samsung or another S Korean brand?

 

What camera is this? That can tell alot.

 

PS. BLC on also makes the image slightly brighter

requires power off and on typically

[CollinR 0]

I guess I will expand a little bit, one foot candle (light of one candle from one foot away) is about 10.75 lux.

 

So as you can see to have something like .3 lux rating you would need to be able to read a piece of paper 1 foot away from the camera and light source (which basically need to be in the same space) and the light source having approx 27/1000th of the light of a conventional candle.

 

27 thousanths of a single candle's light output, thats a very small amount of light.

 

.3 is realistic I guess, 1 foot isn't that far away.

.0000000000000000005 and stuff is totally BS, not possible.

 

 

Boggle yourself with the .002 Sens-Up value.

[photys 0]

Samsung Techwin SDC-415.

Not a true day night.

Im using it as a baseline camera to learn from.

 

Product page

http://www.samsungtechwin.com/product/pro_view_eng.asp?pro_uid=626&cat_uid=14&cat_biz=CTV&cat_lev=AA

 

PDF:

http://www.samsungtechwin.com/product/file_data/manual/20060524_0_0602.SDC-415.E.cata.pdf

[photys 0]

Collin, that clarified the situation a bit

 

The sens-up is an amazing yet useless function in this cam.

It lets you up the exposure time by degrees.

 

I pointed the camera in a very dark area where I couldn't see a thing.

Full sens-up + AGC showed the area in almost daylight conditions but with extreme noise and 1 frame per 3 seconds.

 

Sens-up is exposure time.

Can be used to dodge the noise high AGC adds to an image.

 

Heres where it works:

Set the camera on low AGC to keep a low signal noise and add a slightly longer exposure.

Gives 15 fps, minimal noise and a bright picture.

[rory 0]

many old Box and Zoom cams let you set the exposure manually, mainly the OSD versions. Did that on a Zoom camera a few years back to test .. saw more, but slow. When you add that already slow camera to a DVR without real time, it gets even slower.

[photys 0]

Damn.

Good point.

No way of syncing those 15fps.

 

Ah well, at least my mind is in motion.

[rory 0]

Damn.

Good point.

No way of syncing those 15fps.

 

Ah well, at least my mind is in motion.

 

[CollinR 0]

Point it at a moving fan and enjoy the show.

 

It's a decent enough idea but everything we capture moves.

[CameraGimp 0]

I used to test CCTV cameras and publish lux levels for specifications so have some knowledge of these things. Firstly I'll agree with anyone who says don't trust published lux levels from manufacturer unless you know that both test in the same manner it isn't fair to compare lux levels. It is fair to use figures from independent tester such as magazine reviews but then you should only use these figures to show relative performances. You can't use them to say what image you will get in the real world at 1 lux.

 

Here are the factors you need to know for a sensitivity test to be valid.

The brightness of the light source, obviously

The colour temperature or type of light used. If my camera was sensitive to IR would it be fair to quote a lux level if my light source included IR? Dimmed tungsten is warm and has more IR than filtered fluorescent.

The reflectivity of the test scene. If you are viewing something that reflects better you will see more.

The fstop of the lens.

The signal level coming out of the rear of the camera.

 

My specifications listed the lux level that was needed to give a certain signal out when viewing a scene of 80% reflectance in a quoted fstop lens. Even I didn't quote the colour temperature of my light.

 

Here are the ways that manufacturers vary (cheat?) figures. Drop the signal level, say 30 IRE instead of 40 IRE. You need less light to achieve this so you lux level is lower. Use a faster lens. So beware!

 

On the question of should AGC be on or off? I say on for this reason. If a camera is tested with AGC off you are in effect testing the sensitivity on the CCD only. There is very little any camera manufacture can do to alter this apart from cool the CCD which no one is going to do. So a cheap camera with the same Sony CCD will perform as well as the most expensive with the same chip. AGC is where the good cameras stand out. A good camera will have better signal to noise than a cheap on. When the light level drops and the signal is low you need good snr to keep the image useable. Unfortunately testing images with agc on is subjective. I could make a camera with very high gain and view a scene at low light and achieve a signal of 40 IRE but I might not actually have a useable picture. Ultimately the true test is to put cameras side by side.

 

On the point that BLC makes the image brighter. It may well do so but this is nothing to do with sensitivity. BLC changes the way a camera sets its exposure algorithm. A certain image may become brighter as the camera has changed it's exposure but another scene could cause the image to darken. Neither will change sensitivity.

 

Hope this makes sense

 

CG.

[Ascend 0]

Very well said.

[rory 0]

So a cheap camera with the same Sony CCD will perform as well as the most expensive with the same chip.

 

Has to be the same exact chip, for example, there are variations of Exview chips that run from cheap to expensive. Even so, I would still not say they would perform the same.

 

Take 2 Computers for example, same Intel Chipset, Both with Core 2 Duos. The one with the cheaper Core 2 duo is definitely going to be slower. Ofcourse one can tweak Windows like mad to make it perform close to if not better than the faster more expensive one running with default Windows, but still not the same thing, as that same faster one could also be tweaked and then it too would be even faster. Features play a big part, but unless the hardware is up to spec to begin with, then its not really a fair comparison.

 

Also, I never leave a camera with AGC enabled, as it is fine for nighttime, but daytime is useless, at least down here. Personally when I test a camera I always test it with AGC disabled, as thats how it will be in the field.

 

As to BLC, I agree, I was just putting that out there for the OP so he would at least realize that when he leaves that enabled, when there is light, typically it will be a brighter (glare) image. I always leave that disabled.

 

PS. good post btw, and welcome to the forum

[photys 0]

Welcome to the forum CameraGimp.

Glad to meet you.

 

Those comparative tests sound interesting. Can any of them be made available to us?

 

Regards,

photys.

[CameraGimp 0]

Hi Guys,

 

Rory - Yes you are right about the chips, in my defense I meant the same as you but wasn't clear in the way I said it. Two cameras with identical CCDs will perform pretty much the same with AGC off, two different types of Exview will perform differently. I haven't been involved with CCTV cameras for nearly 3 years now so I am out of touch but in my day there weren't different flavours of Exview. It was HyperHAD, SuperHAD and ExviewHAD. There was a new Exview just on the horizon when I left but I never tested it. Due to the time I've been away I'd say all my tests would be out of date (and I don't have any anyway!)

 

Here's an interesting technical point for you in the form of a question. If you have two CCD's that are identical except for the resolution (standard resolution and high resolution), will there be any difference in sensitivity and if so why?

 

I am pretty amazed to hear that you do not turn AGC on in the field. I worked for a camera manufacturer and it is possible that I suffered from iving in an ivory tower syndrome but I would have bet money on most installers turning AGC on. I am slightly puzzled by this line in your post.

 

Also, I never leave a camera with AGC enabled, as it is fine for nighttime, but daytime is useless, at least down here. Personally when I test a camera I always test it with AGC disabled, as thats how it will be in the field.

 

Are you saying that AGC effects your camera in daytime? It shouldn't, can you confirm.

 

Ta.

[rory 0]

Are you saying that AGC effects your camera in daytime? It shouldn't, can you confirm.

 

Ta.

 

Yep. Image is too bright when the sun is out, this is the same with all brands and cameras I used.

[CameraGimp 0]

Hi Rory,

 

That is really weird. If a camera is set up in a well lit scene the video level should not change when AGC is turned on. If it does then something is wrong with the camera or the way it is set up but as you see this with all cameras I am worried that I am pointing a finger at the way you set up cameras.

 

A camera producing 1v pk-pk video a camera will not apply AGC. (unless you are using something like BLC that changes exposure and even then it is unlikely).

 

If the video level increases when AGC is switched on (on a well lit scene) I would say the lens level is set too low. Sorry to question you on this.

[rory 0]

Going by the major brand name box cameras, they have something called S-AGC. That is mostly what I am talking about, S-AGC ON, S-AGC Off

 

If the camera cannot perform without AGC on, then I dont want to use it. The sunlight here during the day is enough to blind you. So basically going back to Photo's original question, I personally rate the cameras without AGC manually turned on (S-AGC or otherwise). I do adjust the lens accordingly also, but thats another thing.

 

Anyway, the brightness in the image outdoors increases when AGC is turned on with all the cameras I have used, well lit scene or not, doesnt matter how the lens is adjusted, same always. Been a while now though since I used box cameras so things may have changed especially with the OSD in most cameras now, along with other features and new technology.

 

Unfortunately some of the new Korean cameras require their form of AGC to be turned on for their Sens up or Night mode to work, but I dont use those cameras though.

 

Box cameras I used were GE and Sanyo. I've also tested a couple others but never actually used them in the field.