Gain Control / AGC for Video Surveillance Guide

Author: IPVM Team, Published on Apr 23, 2015

Gain control is a critical, though often overlooked, factor in low light surveillance video. It is generally only noticed when the negative side effective of aggressive gain levels are seen, namely noise / snow on screen. The picture below, from one of our parking lot tests, is a prime example of this problem:

Clearly, the noise is a problem and ideally you would want to remove it. This raises important questions about how to use gain control effectively.

In the introductory video below, we provide a real-time demonstration of gain control:

To learn more, we conducted a series of experiments in a variety of scenes. For each scene, we captured video, images and bandwidth consumption. Here are the scenes we tested:

  • Black and White Mode .5 Lux (Dark)
  • Black and White Mode 20 lux (Low Light)
  • Color Mode 4 Lux (Moderately Dark)
  • Color Mode 300 Lux (Daytime)

Our testing was done across 3 HD cameras from Avigilon, Axis and Bosch to see a range of performances.

Inside the Pro section, we share our results and answer the following key questions:

  • How significant does image quality vary with different gain control settings?
  • Should you use gain control?
  • What is the right gain control settings to use?
  • What alternatives should you seek to using gain control?
  • How do manufacturers approach to gain control differ?
  • How does gain control differ between Black & White and Color modes?
  • What is the bandwidth impact of different gain control settings? What impact does light levels have on bandwidth impact?
  • What impact do VBR and CBR streaming modes have on using gain control?
  • What impact does digital noise reduction (include 2D and 3D DBR) have?

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** ***** ****, ** ********* * ****** ** *********** ** a ******* ** ******. *** **** *****, ** ******** *****, images *** ********* ***********. **** *** *** ****** ** ******:

  • ***** *** ***** **** .* *** (****)
  • ***** *** ***** **** ** *** (*** *****)
  • ***** **** * *** (********** ****)
  • ***** **** *** *** (*******)

*** ******* *** **** ****** * ** ******* **** ********, Axis *** ***** ** *** * ***** ** ************.

****** *** *** *******, ** ***** *** ******* *** ****** the ********* *** *********:

  • *** *********** **** ***** ******* **** **** ********* **** ******* settings?
  • ****** *** *** **** *******?
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  • **** ************ ****** *** **** ** ***** **** *******?
  • *** ** ************* ******** ** **** ******* ******?
  • *** **** **** ******* ****** ******* ***** & ***** *** Color *****?
  • **** ** *** ********* ****** ** ********* **** ******* ********? What ****** **** ***** ****** **** ** ********* ******?
  • **** ****** ** *** *** *** ********* ***** **** ** using **** *******?
  • **** ****** **** ******* ***** ********* (******* ** *** ** DBR) ****?

[***************]

Key ********

***'* ***** **** *** *** ******** ** *** *****:

  • Gain ******* **** *********: In almost any night time scenes, without gain control, surveillance video would be very dark and almost practically useless. While gain control is generally ignored, its role is critical. In low light conditions, trying to turn it off to remove the grain/noise will only result in far worse video quality.
  • Gain ******* ** *********: As the name states, Automatic Gain Control, is automatically controlled by almost every camera. While it can produce lots of noise, disabling it generally will make things even worse.
  • Aggressive ***: Unlike in ********** *********** ***** **** ********* **** ********* *** ** **********, ************ ****** ************* **** to *** ******* ******* ** **** *******. **** ** ********* because ****** **** **********, ** ** **** **** ** ******* scene ******** ** ************.
  • Adjusting **** *******: If you want to minimize the bandwidth impact and visual noise inherent in gain control, the two gain adjustments possible are (1) fixing the gain or (2) capping the gain. The former is dangerous unless you can guarantee constant lighting. The latter, assigning a cap, can be useful.
  • Gain *** *&* *** *****: Both B&W and Color modes use gain and display similar characteristics - bandwidth spikes, visual noise, etc. The big difference is that cameras activate gain at much higher light levels for color than in black & white modes (color at ~50 lux, b&w at ~20 lux).
  • Gain *** ********* ********* ******* **********: As gain increases, bandwidth increases as well in a hockey stick curve. Interestingly, this appears to occur regardless of the light level or mode used.
  • Use ***: Since bandwidth is nearly guaranteed to spike as gain increases, we strongly recommend setting a ******* *** ****.

***** ** * ***** **** ***** *** ******** *** *** findings **** ********** ** *** **** ***** *** ******:

Configuring *** ********** ****

**** ** ********* ********** ** *** *****:

  • ******:*** *******, ****, ******, *** - **** ** * ****** grained *******.
  • **:*** *******, ***, ****, ****, ***. * **** **** *******, the ***** ***** ** ** **** *** (***) ** **** or ****** (**** **********).

**** ** ********** ********* ** *** ** ***** **********:

  • ****:** *******, **** ******* ************* ********* **** ***** **** ****** be.
  • *****:** ** ***********, * **** *** **** **** ** * specific ***** (*.*., ****** * **). **** *** ** ********* - ** *** ** **** ** *** *** * ***** (like ***) *** *** ***** ******* **** ********** **** (*** 5 ***), *** ***** ******* ** ***** ** ** ***** poor. ** *** ***** ****, ** *** *** ** ** a **** ***** (*** ** ***) *** *** ***** ******* bright, *** ***** **** ** ********* ** ***** ***** / noise.
  • ***:**** ******* ***** *** ***** ** *** *** ******* **** the ****** *** ******. **** ****** *** ****** *** ******** to ********* *** **** *** ****** ** **** ***** *** high *** ** *****'* **********. **** *** ** ****** *** reducing **** ****** ***** *** ******** ********* ******. *******, ** course, **** ** **** **** **** **** **** *** ***** darker **** ******** **** *** ****.

*** ***** ***** ******** ************** ** *** ** *** *** optimize **** ***** **** *** ***** ******* ** ** *******:

Gain *** ********** ****** *************

******, **** ** * ************* **** *** **** **** ****** (e.g., **** ** ****), ** **** *** **** **** *** the '****' ** ******* *** '****' *** ***** ***********. *** they *** **** / ******* ***** *** ****** ****.

Gain *** ***** *** ***** ***********

*** *** ** ***** ** ************* ********* ***** *** ***** performance, **** ***** **** ***********, ************, *******, ***********, ***. *** of ***** *** ***** ******** ***** ** **** ******* ** improve *** ***** ***** *******. *******, **** '***********' **** *******, they **** ** ******** ********* *********** ******* (****** ** *** much ****** ********* ** ******** ********* ************** ***). ***** *** ***** **** ***, *******, ******* ** nor ******* *******. *** ******* ************* ***** **** ******** **** control / ***** **********.

**** *** *** *** ***** *** **** ****** ** ******** abstractly. *** *** ****** *** *****, *.*.,***** *** ***** ** ********** ** *********** ********** ****** ******* ** *** ***-***** ***********.

Varying **** ******* **************

** *** * ***** ** *** **** ******* ******* ***** quality, *** ***** *********** **** *** **** ***** **** *** same ******** **** ********* **** ******. *** *** ***** *** the ******* ****** ** **** **** **** ********** ***** ** a ***** **** *****. **** * ****:

** *** ***** *****, ****** ****** ***** ***** **** *** top ***** ** *** ****. **** **** **** *****, **** gain ******* ******** ** **** ******** ***. ******, **** **** 3dB ** ****, *** ***** ** ***** *****.

***'* ******** ** ******* ***** ***** **** *** *** ****** of *****. **** * ****:

***** ** *** ***** ** ******? **** *** ** ********* much **** ******* **** *** ***** ***** **** *** * lux ********. ** **** *****, **** ** ***, *** ***** with ******* **** ** ******** **** *** ******* **** * lot ** ****** *****. *** ****** ******** **** ****** **** less ****, ****** *** ***** ****** ***** ** *** *** gain ****** **** ****. ** * ***** ** *********, ** estimate **** ******'* ********* **** ******* *** **** ***** ** be ***** * ** * **.

Color **** - **** ******

*** **** ********* **** **** ******** ****** **** ***** ****. The *** **********, ** *** ********** ***** ***** ** **** with *****, **** ** ****** **** **** ** ****** ***** levels. ** *******, ** * ***, *** * ******* ************* adjusted ***** **** ******* ** ******* ******. *** *** *** this **** *** ***** ******* ***** ****** **** *****.

color mode-gain max vs disabled 4 lux

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Gain's ****** ** *********

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***** ** ****, ** ********* *** ***** **** *** ***** bandwidth ***********. ** ** ** ***** ****, *** ** * gain ******* *** ****** *** *** ******** ** **** *** manufacturer's ******* *******.

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bandwidth impact at max gain

Gain ****** ****** *******

*******, **** ** * ******* ********** ** **** ****** ***** levels, **** ******** *** ******* ******. **** * **** *** compare *** *********** ********. ******* *** **** *********** ******* ** saw **** *** **** **** ****** ***** (*** *** ** the ****** ** *** **********), *** ******** ******* ** ******* the ******** ***** *******. *******, **** *** ****, ********'* ***** essentially **********.

impact of varying lux and gain across cameras

Digital ***** ********* *** ****

** ******* *** ****** * ********** ** ****** *** ***** generated ** **** **** ******, ***** ** ******* ***** ********* (DNR).

*** **** ** ****** ******* ***** ** ********** ********** ****** (2 ***********) ** ****** * ****** ** ****** (* ***********) to ******** ***** ******* ** ***** ** ********* **** ** and ** *** *****. ** ******** ******* ***** ** *** image, ********* ************ *** **** *******, ********* ************.

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*** **** *******, *** ********* ******* ***** ********* *************** ********* **. *** *****.

Quiz ******** ** *** / ****

**** *** *** / **** **** ***.

Comments (12)

Note: The first version of this post was written in 2011. We have updated it significantly adding in sections about 'super low light' and digital noise reduction, two key technological advances that have occurred in the past 4 years.

I wondered where the intro splash for the video was...?

Interestingly Axis eliminates the need for DNR thru meticulous cooling:

...digital noise reduction is widely used in image processing techniques to eliminate visible noise. The purpose is to improve image quality and lower the bandwidth used for encoding...

Axis has chosen a different approach. The image sensor is meticulously cooled and in doing the need for digital noise reduction is eliminate. The advantage of this system is that it does not need any computing power or extra equipment, such as fans. Instead, it removes the noise ‘from the source’. Beyond Standards - Axis 2015

IMHO, Axis images are typically sharp (except for 4K) but gritty, this might explain why.

Since relying on a mfr's SNR is, at best, useful as a relative measure within a mfr, what is the best way to measure/compare noise in general?

Does anyone know the reason the 20lux image gets darker from the 18db to the 27db? Is the iris or shutter going too far in trying to compensate for the excessive gain?

After a quick review I was a little surprised there was no mention made of what the effect of AGC noise can have on motion detection recording. The turning OFF of lights in a room, in an effort by customers to save power costs and be more 'green'', will almost without doubt cause unwanted, false triggered, recording(s) of non-occupied areas, thus impacting hard drive space and calculated retention of video data.

AGC noise can be a problem, but we didn't find it to be major in our tests. In fact, of the seven manufacturers we tested (Avigilon, Axis, Bosch, Sony, and Dahua, Hikvision, Samsung), none of them frequently triggered based on noise in dark scenes. Opening or closing a door or someone walking by a window in a lit hallway triggered motion, yes, but pure noise, no.

Compared to years ago, when we originally tested VMD, this is much improved.

Also, with integrated IR becoming more and more popular, lower gain levels and less noise are becoming more common, since the illuminator adds usable light to the scene.

I'm not saying it can't happen, and I'm sure it does, but at least for cameras I see lately, the problem of all night recording due to noise is at least reduced.

This link could not be found - 'commercial videography where gain control'

Christophe, thanks. It looks like in the past half year that the site linked to was shut down or bought. Here is a link to the archived 'commercial videography where gain control' article.

Good writeup

Good pictures to show the differentiation.

Interesting to know the table comparison between different camera vendors on the bit rates with DNR feature on and off...

Getting better understanding in the relationship between bandwidth and gain.

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