Adjusting the Field of View of MV Cameras
Overview
This article explains features and terms relative to field of view (FoV) for Cisco Meraki MV smart cameras. A comparison of camera features is provided, along with steps to configure camera features to achieve the best image quality.
Functions that modify the field of view
MV smart cameras have three ways of adjusting their FoV:
- Sensor crop
- Optical zoom
- Digital zoom
Understanding the differences between these features and how to use them together helps achieve the best image quality.
Imaging basics
Light within a certain FoV enters the lens of the camera. The focal length of the camera dictates the FoV. Cameras can have either a fixed or varifocal lens. Varifocal lenses adjust the focal length to produce a wider or narrower FoV, which is how optical zoom is implemented. Fixed lenses do not have optical zoom because the lens cannot be adjusted and maintains the same FoV.
After light enters the lens, the image sensor (image plane) captures the light. The camera then scales the captured image down to the desired resolution (720p or 1080p) to produce the stream. Sensor crop is implemented at this stage.
Digital zoom is a post-processing technique that crops a region and adds estimates of pixels through bilinear interpolation. Digital zoom is performed on the image after the sensor has captured it.
Definitions
Sensor crop
Sensor crop sets a fixed zoom and pan while maintaining the same image quality. Refer to the article Sensor Crop for more information.
Optical zoom
Optical zoom moves the lenses to magnify a far-off image and fills the entire image sensor with the magnified image. The number of available pixels to capture an image remains the same at any zoom level.
Digital zoom
Digital zoom performs post-processing on the captured image, to crop it and stretch out the pixels. In the Meraki dashboard, bilinear interpolation adds new pixels between existing pixels based on the values of the nearest neighbors. Digital zoom does not add any additional detail to the photo.
Comparison
|
Optical zoom |
Sensor crop |
Digital zoom |
||
|---|---|---|---|---|
|
How it works |
What changes? |
Focal length of the lens (optics) |
Region to scale for the desired resolution (after optics, but before processing) |
Region seen on the dashboard video stream (post-processing) |
| Requires physical moving parts within the camera? | Yes | No | No | |
|
What it does |
How does it affect the image? |
Narrower or wider field of view |
Cropped regions are not captured |
Pixelation and loss of image quality when viewing the feed on the web portal (no change to historical footage) |
| Adds detail? | Yes | Yes | No |
Configuration
Follow these steps to configure the FoV on an MV smart camera:
- Configure the optical zoom to capture the desired FoV.
- Use sensor crop to further remove unwanted areas at the top, bottom, or sides.
- During operation, apply digital zoom in the dashboard using the mouse wheel scroll or the "+" magnifying icon options when hovering over the video, to closely examine specific parts of the image.
Step 1: Optical zoom
Under the camera's settings page, configure the optical zoom to capture the desired FoV. The optical zoom option as shown on the dashboard:
Example image at 0% zoom:
Example image at 99% zoom:
After making optical zoom changes to cover the desired FoV, refer to Focusing MV Cameras to adjust the focus.
Step 2: Sensor crop
The sensor crop option as shown on the dashboard:
Before sensor crop (with crop region shown):
After sensor crop:
After making sensor crop changes to cover the desired FoV, refer to Focusing MV Cameras to adjust the focus.
Step 3: Digital zoom
To apply digital zoom during operation, use the mouse wheel scroll or select the "+" magnifying icon when hovering over the video feed in the dashboard. Zooming in and out, as shown on the dashboard:
