Comparison of Axis 223M and Mobotix 12M

[Sawbones 0]

Amir? Your posts are absolutely stellar. Thank you very much for taking the time.

Thanks for the kind words Sawbones.

 

While I am posting this, here is a pop quiz: what are those horizontal lines on the black and white picture Marc posted just above?

 

Only guessing here... but are those actually the scan lines?

 

They're even visible (though subtle) in the well-lit areas of the picture (against the side of the vehicle, and on the porch post). I would have suspected some digital noise in a dark scene, but I wouldn't expect that in the better-lit portions.

[amirm 0]

Only guessing here... but are those actually the scan lines?

Good guess but no. Well, OK, it has a remote connection . Note that the camera fetches those pixels the same way all the time. So their appearance in this example versus others has to be something else...

 

I will post the answer soon if no one else wants to guess....

[Monitor Your Assets 0]

Power supply frequency?

[amirm 0]

Power supply frequency?

Another good guess. But no, that is not it. OK, that could also be remotedly related .

 

Come to think of it, power supply noise could also contribute to this....

[cglaeser 0]

The 0.1 lux at 1/60 is applicable for any camera with a night lens

 

No doubt the dedicated B/W lens is a big help for the M12D. The Axis 223M can not come anywhere close to this performance. I would estimate it requires at least 7 stops more light. Each stop is 2x, so 7 stops is 128x more light. Or, approximately 0.1 lux in 2 seconds. Two second exposure time is an eternity when someone is walking; subjects are just a wispy blur.

 

Would love the opportunity to measure the M12D SEC in low light.

 

Best,

Christopher

[Sawbones 0]

Is it safe to assume that the Mobotix's dedicated night camera is IR sensitive?

 

I have a major investment in IR around my home, so that's important.

[amirm 0]

Is it safe to assume that the Mobotix's dedicated night camera is IR sensitive?

 

I have a major investment in IR around my home, so that's important.

From the documentaion yes. The way they get more sensitivity is to remove the IR filter which is necessary for color CMOS sensors for proper color reproduction.

[Monitor Your Assets 0]

From the documentaion yes. The way they get more sensitivity is to remove the IR filter which is necessary for color CMOS sensors for proper color reproduction.

 

Agreed! In the URL below, Mobotix even includes some lighting tips.

 

http://www.mobotix.com:80/eng_US/Products/Camera-Functions/Day-Night

[Monitor Your Assets 0]

The 0.1 lux at 1/60 is applicable for any camera with a night lens

 

No doubt the dedicated B/W lens is a big help for the M12D. The Axis 223M can not come anywhere close to this performance. I would estimate it requires at least 7 stops more light. Each stop is 2x, so 7 stops is 128x more light. Or, approximately 0.1 lux in 2 seconds. Two second exposure time is an eternity when someone is walking; subjects are just a wispy blur.

 

Would love the opportunity to measure the M12D SEC in low light.

 

Best,

Christopher

 

Hi Christopher,

 

I hope to have some time this week to provide some samples with my M12D-IT at night with different exposures. In the mean time, here are a few (!) Mobotix cameras that are open to the public. Unfortunately, there is no way of filtering for M12D SEC cameras.

 

http://www.123cam.com/category-webcam-Mobotix.html

[amirm 0]

OK, here is the answer to the quiz.

 

When there is very little light, the camera increases the "gain" (amplification) of the sensor quite high in order to extract the tiny amount of signal coming from it. The lines get created due to noise in the rest of the camera bleeding through the analog gain stage. The noise is random to the extent that what the camera is doing from line to line may be different (e.g. outputing something on Ethernet port or not).

 

So yes, having power supply noise or reading the pixels using certain logic all contribute to noise which shows up in the final image.

 

While we are on topic of noise, the lower the temprature, the less of it in the image! So your camera will work better in winter than summer. And proper comparison of two cameras requires that they both be run at the same temprature....

[griffonsystems 0]

do this google search and you will find all the mobotix m12 cameras you can take:

 

intext:"MOBOTIX M12" intext:"Open Menu"

 

argentina beach on a scanner - could be interesting in the summer

 

http://cvcogoleto.dyndns.org/cgi-bin/guestimage.html

[cglaeser 0]

When there is very little light, the camera increases the "gain" (amplification) of the sensor quite high in order to extract the tiny amount of signal coming from it.

 

No doubt the high gain is causing the high noise, but it's possible the firmware could be contributing to the horizontal banding. The IT uses the same sensor as the SEC, and the megapixel image is converted to VGA in firmware. If the algorithm uses a relatively simple approach of combining pixels along a horizontal row, that would introduce banding.

 

BTW, that's why the IT and SEC have identical minimum illumination specs. They use the same sensors.

 

Best,

Christopher

[amirm 0]

No doubt the high gain is causing the high noise,

Just clarifying. The banding is different than noise due to high gain. The sensor noise would be random and not lines. It is the side effect of the input amp being at highest gain point (and signal at lowest point) which allows noise from the rest of the camera (which would have more regular pattern) to be picked up.

 

but it's possible the firmware could be contributing to the horizontal banding. The IT uses the same sensor as the SEC, and the megapixel image is converted to VGA in firmware. If the algorithm uses a relatively simple approach of combining pixels along a horizontal row, that would introduce banding.

It is true that improper resizing causes quantization noise (banding as you call it). However, that kind of banding has a very different look. And further, would occur whether the camera is picking up low light or full sun. If you look at the daytime shots, there is no banding at all. So no, this banding is not due to resizing distortion.

 

BTW, that's why the IT and SEC have identical minimum illumination specs. They use the same sensors.

I suspect you are right but I don't know for sure. If it is using the same three megapixel sensor, then it will have a better signal to noise ratio than its SEC brother since the process of resizing will act as noise reduction. Reason is that proper resize algorithm would filter high frequencies and noise spectrum likewise gets filtered down. Let's look at this in detail.

 

Imagine if you resized the image by half by adding two adjacent pixels and divided by two to get your new pixel. Now look at the scenario of one black pixel and one noisy pixel right next to it (typical situation in a low light situation). Add these two together and divide by two. What do you get? The new pixel will have half the intensity of the noisy pixel (0 + N = N/2)! This kind of filter is not that great in practice so it typically is not used but should give you an idea of why a resizing filter like this reduces noise.

[Monitor Your Assets 0]

Hi Chris,

 

I finally got around to the "exposure experiment" where I captured low light motion with three different maximum exposure times: 1/10, 1/30 and 1/60 which seems to be the sweet spot. You won't be able to recognize a face in the image, but instead, a partial license plate is exposed. All images were taken while briskly walking up the stairs. For reference, the distance from the camera to the closest pole (where it meets the rail) is 20'.

 

This experiment was done twice - once with the outside house lights on (~0,8 lux) and once off (~0,4 lux). The links below include 3 images each as an animated GIF so that one can see the difference. Each image includes the available light and exposure time as well.

 

Enjoy!

 

M12D-IT exposure samples w. little light

M12D-IT exposure samples w. less light

[cglaeser 0]

Just clarifying. The banding is different than noise due to high gain. The sensor noise would be random and not lines

 

Right, we agree, the banding is not due to high gain. That's why I provided a different explanation than your original answer.

 

It is true that improper resizing causes quantization noise (banding as you call it). However, that kind of banding has a very different look. And further, would occur whether the camera is picking up low light or full sun.

 

Take another close look at the sunlight photo of the car. Look at the high contrast diagonal parts of the car wind shield and front bumper. See those horizontal bands near the high contrast transitions? Those bands do not appear in the SEC model, and yet, here they are in the IT model, which uses the same sensor. I'm suggesting those bands were introduced by the firmware when the megapixel image was reduced to a VGA image, and at night, those bands are amplified by the high gain.

 

I suspect you are right but I don't know for sure.

 

I asked Mobotix tech support and they confirmed it.

 

Best,

Christopher

[cglaeser 0]

I finally got around to the "exposure experiment"

 

Excellent! Thanks for posting this. Do you by chance have access to a photography light meter? I know the Mobotix is reporting reflected lux values, but it would be great if we could independently measure the ambient lux value.

 

Best,

Christopher

[Sawbones 0]

Hi Chris,

 

I finally got around to the "exposure experiment" where I captured low light motion with three different maximum exposure times: 1/10, 1/30 and 1/60 which seems to be the sweet spot. You won't be able to recognize a face in the image, but instead, a partial license plate is exposed. All images were taken while briskly walking up the stairs. For reference, the distance from the camera to the closest pole (where it meets the rail) is 20'.

 

This experiment was done twice - once with the outside house lights on (~0,8 lux) and once off (~0,4 lux). The links below include 3 images each as an animated GIF so that one can see the difference. Each image includes the available light and exposure time as well.

 

Enjoy!

 

M12D-IT exposure samples w. little light

M12D-IT exposure samples w. less light

 

Those are great! Thank you.

[Monitor Your Assets 0]

Do you by chance have access to a photography light meter?

 

No, sorry.

[cglaeser 0]

Here's an image taken with the Axis 223M at dusk.

 

http://tinyurl.com/bfy4u7

 

I waited as long as possible to take the dimmest light that might be usable for identification purposes. The light meter indicates ISO 400, 1/4 second, f/1.4.7 (this meter can measure fractional f stops). That corresponds to about 7 lux.

 

The Axis is set to 1/50 shutter speed and 36 gain. IMO, 1/50 is the slowest shutter speed possible to keep motion blur under control. Setting the exposure time to anything longer (e.g. 1/25) causes too much motion blur to really be useful.

 

I think this image is barely usable at 7 lux. At 1 or 2 lux, the image is too dark with too much noise. The Axis brochures indicates a minimum illumination of 0.2 lux, which is considerably less than 7 lux. Why the huge difference? Because they are using an exposure time on the order of 2 seconds.

 

Here's an example of me walking very slowly when the exposure time is set to 1 second.

 

http://tinyurl.com/b43297

 

Is that me, or is that the dog standing on hind legs?

 

More important, is this really a day/night camera?

 

Best,

Christopher

[ak357 0]

Here's an image taken with the Axis 223M at dusk.

 

http://tinyurl.com/bfy4u7

 

I waited as long as possible to take the dimmest light that might be usable for identification purposes. The light meter indicates ISO 400, 1/4 second, f/1.4.7 (this meter can measure fractional f stops). That corresponds to about 7 lux.

 

The Axis is set to 1/50 shutter speed and 36 gain. IMO, 1/50 is the slowest shutter speed possible to keep motion blur under control. Setting the exposure time to anything longer (e.g. 1/25) causes too much motion blur to really be useful.

 

I think this image is barely usable at 7 lux. At 1 or 2 lux, the image is too dark with too much noise. The Axis brochures indicates a minimum illumination of 0.2 lux, which is considerably less than 7 lux. Why the huge difference? Because they are using an exposure time on the order of 2 seconds.

 

Here's an example of me walking very slowly when the exposure time is set to 1 second.

 

http://tinyurl.com/b43297

 

Is that me, or is that the dog standing on hind legs?

 

More important, is this really a day/night camera?

 

Best,

Christopher

 

Which light meter do u use ?

Thanks

[cglaeser 0]

Which light meter do u use ?

 

I use a Minolta IV, but pretty much any photo light meter will do. You can find conversion tables on the net that will convert ISO/shutter/f-stop to EV to lux.

 

Best,

Christopher

[ak357 0]

Which light meter do u use ?

 

I use a Minolta IV, but pretty much any photo light meter will do. You can find conversion tables on the net that will convert ISO/shutter/f-stop to EV to lux.

 

Best,

Christopher

 

Thx

I use extech it has foot-candles and lux scale