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Choice of camera model according to known scene illumination

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Choice of camera model according to known scene illumination

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Choice of camera model according to known scene illumination

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See before: About camera sensitivity

 

Problem

 

There is a black/white mini camera with known sensitivity parameters: Minimum scene illumination 0.04 lx with lens F1.2 at signal/noise ratio=10dB, IRE30.

 

Mini lens F2.0 is mounted on the camera.

 

At night the scene is poorly illuminated by the illuminator with a mercury high pressure lamp, placed far from the scene. Illumination measured by the luxmeter is 0.1 lx.

 

It is required to obtain and evaluate image model from the camera.

 

Solution

 

1. Create camera by clicking the Create camera button and place it on layout.

 

2. Modeling the scene.

 

2.1 Open the 3D Video . Enable Image processing if it is disabled.

2.1.1 Click the 3D model  button and place some different 3D models in front of the camera.

 

3. Modeling scene illumination.

 

3.1 By right clicking or double clicking on the 3D Video open the Image parameter panel, open the Scene tab. On the Scene tab switch to the Night tab.

 

On the Night tab:

 

3.1.1 Mark the Model illumination box.

3.1.2 Select in the combo box Background light source = Mercury high pressure.

3.1.3 Select in the combo box Background illumination (lx) =0.1.

 

4. Modeling camera sensitivity.

 

4.1 Open the Sensitivity and resolution . box. In the box select sensitivity parameters on the Camera panel:

4.1.1 Color = black/white.

4.1.2 Minimum scene illumination (lx) =0.04.

4.1.3  At aperture =F1.2.

4.1.4 S/N (dB)=10.

4.1.5 IRE = 30.

4.1.6 exposure (ms) = 20.

4.1.7 Mark the AESC (electronic shutter), AGC (automatic gain control) and Gamma (gamma correction) boxes.

 

4.2 On the Lens panel choose:

4.2.1 Fixed iris.

4.2.2 Aperture limits = F2.0.

 

5. In the 3D Video we see image model and calculated values: signal amplitude 20 IRE and signal/noise ratio (S/N)=2.31dB.

 

Visually the image is unsatisfactory. 3D models are lost in noise.

 

6. Select more sensitive standard design camera with a higher aperture lens: minimum scene illumination 0.04 lx with lens F1.2 at signal/noise ratio=17dB, 50 IRE. The lens F1.2 is mounted on the camera.

6.1 Specify its parameters in the Sensitivity and resolution box and see the image model. Visually image quality at the night time is quite acceptable. Calculated parameters: S/N=17dB, 51 IRE.

 

It is possible to specify resolution parameters, check possibility of 3D model detection and identification at known distances.

It is recommended to perform the test with 3D model of a black man.

It is recommended to set the maintenance factors.

 

External link: "The principles of CCTV design in VideoCAD. Part 4. Illumination and camera sensitivity in CCTV"(*.pdf) .