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Modeling lens distortion

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Modeling lens distortion

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Modeling lens distortion

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There is a difference between the actual values ​​of view angles given in the specification of cameras(lenses) and angle values ​​obtained by calculation.

The reason for the difference is the lens distortion. Distortion can lead to a significant deviation of the view area form from a regular pyramid and warping of the pixel density distribution.

See more: About lens distortion

 

Accounting distortion when designing CCTV provides models of the view areas and images more close to reality, and thus more fully use cameras in the project.

 

 

Camera specifications do not contain a "lens distortion" parameter, therefore VideoCAD simulates distortion based on real view angles, which, as a rule, are given in the specifications.

 

The easiest way is to simulate lens distortion of cameras whose specification contains at least two real view angles (horizontal and vertical). To simulate distortion, it is enough to enter into VideoCAD values ​​of two real view angles and the image resolution in pixels (from the image resolution, VideoCAD will calculate the Aspect ratio).

 

It is somewhat more difficult to model the lens distortion of cameras, the specification of which contains only one real view angle (horizontal). To simulate the distortion, in addition to the value of one real angle, the exact sizes of the active area of ​​the image sensor are required. The sizes of the active area of ​​the image sensor can be determined by other parameters available in the specification, however, this may be difficult for an inexperienced user.

 

See: Specifying active area size of the image sensor.

 

If the camera specification does not contain any real view angles, then the Lens distortion can be simulated only approximately using the real view angles of similar cameras with the same lens focal length and the size of the active area of ​​the image sensor. It is possible to measure real view angles practically.

 

Problem

 

There is a camera AXIS M1045-LW. It is required to obtain a model of the view area, the distribution of the pixel density and image from this camera with taking into account lens distortion.

 

Camera parameters according to manufacturer's specification:

Sensor format - 1/3";
Lens focal length - 2,8mm;
Real horizontal view angle - 110 degrees.
Real vertical view angle - 61 degrees.
Number of pixels 1920x1080 (max)

 

Since the spec contains 2 view angles and pixel resolution, it is possible to simulate lens distortion in a simple way.

 

Order of work

 

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

2. Open the Camera geometry box and specify camera parameters:

Sensor format - 1/3";
Lens focal length - 2,8mm;
Active pixels - 1920*1080.

 

The Aspect ratio combobox must contain 16/9 (1920/1080=16/9).

 

 

3. Click on the button to open the Sensor and Lens box.

In the box, pay attention to the difference between the calculated horizontal view angle - 81.2 degrees and the actual view angle from the manufacturer's specification - 110 degrees. The difference indicates that the lens distortion is present.

 

 

4. On the Lens distortion panel, mark the By two angles and aspect ratio switch. Check the checkboxes Horiz. and Vert then enter into the boxes the known values of the real view angles horizontal (110) and vertical (61).

 

 

5. Turn on modeling distortion, by checking the Simulate checkbox. After that we will see significant change of view area in the Graphics window.

 

Without simulating distortion

With simulating distortion

 

If you set real angle values too differed from calculated angles or set other inconsistency, then the boxed will colored in Red and (or) the view area will be corrupted.

 

6. To observe influence of the distortion on the image from the camera, open the 3D Video and place several 3D models within camera's view area.

 

Without simulating distortion

With simulating distortion

 

7. To observe influence of the distortion on the form of the view area in 3D, open the 3D World .

 

Without simulating distortion

With simulating distortion

 

The pictures show that under the influence of the lens distortion, the field of view expands, but the spatial resolution deteriorates, especially at the edges. Modeling distortion allows this to be taken into account.

 

See also: Sensor and Lens>Lens distortion, About lens distortion, Measuring real view angles, List/Range, Specifying active area size of the image sensor