VideoCAD

Camera Geometry

 Sensor and Lens

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Camera Geometry

 Sensor and Lens

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Camera Geometry

 Sensor and Lens

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The Sensor and Lens panel can be called up by the Sensor and Lens button on the Toolbar or with the same button in the Camera Geometry box.

 

On the panel you can set:

 

list of possible camera resolutions in pixels;
list of values ​​or range of the lens focal lengths.

 

In addition to specifying the lists, the tools on the Sensor and Lens panel can improve accuracy of modeling the shape of the view area, by taking into account:

 

dependence of size of the active area of the image sensor from the selected resolution in pixels;
effects of lens distortion.

 

Applying these tools requires a bit more knowledge about the applied camera model. But manufacturer's specification , as a rule, contains all the necessary information.

 

If an error about 20-30% is acceptable when modeling the shape and size of the view area, then you can neglect these tools, limiting yourself to traditional tools for specifying  the image sensor format, lens focal length and the number of active pixels in the Camera Geometry box.

 

Click to expand
Click to expand

 

Image sensor

 

See before: Image Sensor and Active area of image sensor

 

On the Image sensor panel you can set the size and aspect ratio of the image sensor or size of active area of the image sensor.

Size and Aspect ratio boxes duplicate the Image sensor size box on the Camera geometry window, but allow you to enter the size and aspect ratio in different boxes.

 

In the Size box you can specify the image sensor size by any of the following ways:

 

Choosing a standard format (type) from the list 1/10",1/8",1/6",1/5",1/4.5",1/4",1/3.6",1/3.2",'1/3",'1/2.7",'1/2.5",1/2.3",1/2",1/1.8",1/1.7",1/1.6",2/3",1/1.2",1",4/3",1.5";

 

This traditional way of setting the image sensor size can be unaccurate for modern cameras.

 

Entering a custom format in inches, in the form of X/Y". For example: 1/7.31";

 

If you enter a format which does not exist in the list, the box turns yellow, and the Image sensor size will be calculated by VideoCAD.

 

Entering diagonal size of the image sensor in millimeters, in the form of dX.Y. For example: d6.0.

 

See more: Specifying image sensor size through its diagonal and aspect ratio

 

Entering sensor side sizes in millimeters horizontally and vertically separated by hash, in the form of W#H.  For example: 4.8#3.6;

 

See more: Direct specifying image sensor side sizes

 

In the Format box you can specify the active area side sizes of the image sensor in millimeters horizontally and vertically separated by asterisk, in the form of W*H. For example: 4.8*3.6;

 

See more: Direct specifying active area side sizes of the image sensor

 

In the Aspect ratio box you can specify the aspect ratio of the image sensor in the form of W:H. For example: 16:9 or 4:3.

 

To save changes click Save.

To cancel changes click Cancel.

 

See also: Specifying active area size of the image sensor/

 

Image sensor's active area

 

See before: Image Sensor and Active area of image sensor

 

On the Image sensor's active area panel you can specify parameters of  active area of the image sensor, involved in forming the image.

 

In the List of resolutions box, you can specify a list of possible resolutions of the active camera, in pixels. For the convenience of filling the list, you can call the drop-down form .

 

See details: List of resolution

 

In the Aspect ratio box displays the aspect ratio of the active area of the image sensor. It is identical with the Aspect ratio of the output image of the camera.

 

See more: Specifying the Aspect ratio of output image

 

Set Aspect ratio from pixels - calculate the Aspect ratio as the ratio of the numbers of pixels horizontally and vertically. This rule is not always fair. If the checkbox is checked, then the Aspect ratio of the active camera will be recalculated with each change of resolution in pixels. Changing the Aspect ratio leads to a change in the shape and size of the view area.

 

In  the Crop box you can set the crop factor - the ratio of cropping active area size of the image sensor when the active area does not touch the edges of the image sensor. In other cases Crop=1.

The Crop factor can be set as a vulgar fraction (separated by slash) or a real number. For example 4:3 0.67 or 16:9 720/1080. If the crop factor is not specified, it is taken to be unity.

 

 

See more: Specifying the crop factor

 

The Calculator icon invokes the Image sensor calculator box for convenient calculation of image sensor's aspect ratio, active area aspect ratio and the crop factor.

 

The Horiz., Vert. and Diag. boxes display sizes of the active area of the Image sensor, which are used in modeling the camera.

These sizes are calculated based on the size and aspect ratio of the image sensor, as well as the aspect ratio of the output image.

 

In the boxes, you can directly type any sizes of the active area of the image sensor in millimeters.

In this case, the aspect ratio of the active area will be defined by the ratio of its sizes. The Aspect ratio box will show Custom.

By this method, you can specify an arbitrary aspect ratio of the image and camera angles. To set arbitrary camera angles choose the sizes of the active area of the image sensor.

 

Below you can see the dynamic image showing the position and relative sizes of the active area on the image sensor (aqua color) subject to the selected aspect ratios and crop factor.

 

Examples of images of image sensor of real cameras:

 

Aspect ratio of Image sensor

4:3

16:9

4:3

16:9

16:10

16:10

16:9

(1920*1080)

Aspect ratio of Active area of Image sensor

4:3

16:9

16:9

4:3

16:9

4:3

16:9

(1280*720)

Crop

1

1

1

1

1

1

720/1080=0.67

Image

 

To save changes click Save.

To cancel changes click Cancel.

 

See also: Specifying active area size of the image sensor/

 

Lens

 

On the Lens panel you can see:

 

Lens focal length - the box duplicates the similar box in the Camera geometry.

 

Calculated view angles are calculated from the sizes of active area of image sensor and the lens focal length.

 

Via changing sensor sizes when the lens focal length is fixed, you can set separately arbitrary horizontal and vertical view angles.

 

In the List / Range box you can set a list of possible values or the range of the lens focal length. For the convenience of filling the list, you can open the drop-down form .

 

See more: List/Range

 

To save changes click Save.

To cancel changes click Cancel.

 

Lens distortion

 

See before: About Lens distortion.

 

 

 

As a rule, taking into account lens distortion is relevant for lenses with a focal length of less than 4mm. For long focus lenses, the distortion is usually can be neglected. In cases requiring precision, compare the real view angles (from the camera manufacturer's specifications or obtained by practical measuring) with the calculated view angles displayed in this box. If the angles differ by more than 1-2 degrees, the distortion of the camera lens may be noticeable. You can simulate distortion and evaluate its impact on your task.

 

To specify lens distortion:

 

1. Set or check the correct lens focal length;

 

2. Set or check format or real sensor sizes;

 

3. On the Lens distortion panel mark a checkbox near to a box of known value of real view angle (horizontal, vertical or diagonal) and enter known angle to the box. Clear checkboxes of unknown angles - VideoCAD will calculate them.

 

If real angles calculated by VideoCAD will differ from the real angles from camera specification, you can correct them, by marking a checkbox near to appropriate box. You can also change lens focal length a little. It is not recommended to change sensor sizes to correct real angles.

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.

 

4. Mark Simulate to model active camera taking into account lens distortion.

 

Simulation of distortion for all cameras can be turned on and off in the Options box > Miscellaneous > Lens distortion > Simulate distortion. There, in the Options box, you can change the discretization accuracy of distortion simulation.

 

Attention! Changing the lens focal length or the format / size of sensor at fixed real angles causes view area corruption and requires changing the real angles. Therefore, it is advisable to enable modeling distortion after a preliminary selection of proper lens to increase precision of modeling. To set the actual distortion angles for multiple lenses or for varifocal / ZOOM lenses, use the List/Range string.

 

Under the influence of the lens distortion the view area becomes more complicated, it sometimes becomes infinite . To limit the distance of view area drawing use the Maximum distance of drawing view area.

 

In the 3D Video distortion is modeled with low resolution. You can obtain distorted image model with real resolution by 2 ways:

Check the Real frame size menu item then save image from the 3D Video to a file. The file will have full size, real resolution and distortion.
Use PiP. While distortion is modeled, the particular view of PIP has real resolution. In case of corruption on the corners of image with strong distortion - decrease the size of the particular view.

 

Changing the pixel density under the influence of lens distortion is considered along radial rays from the center of the frame to the edges, without distinguishing between horizontal and vertical.

 

Simulation of distortion increases the demand for computer power.

 

During simulation of lens distortion, the green bold underlined font is used in the lens focal length combo boxes.

 

To save changes click OK.

To cancel changes click Cancel or close the box.

 

See also:About lens distortion Modeling lens distortion, Measuring real view angles of a camera