What Is a Monocular Camera? Single-Camera Vision in Robotics.

What Is a Monocular Camera?

A monocular camera is a camera that observes a scene from a single viewpoint.

In robotics, monocular cameras are commonly used for object recognition, visual navigation, inspection, and tracking.

For example, a warehouse robot may use one forward-facing camera to recognize signs, identify products, or observe obstacles.

A monocular camera captures visual information, but unlike a stereo camera, it does not obtain depth through the comparison of two simultaneous camera viewpoints.

Distance must be estimated using other information or methods.

Key Takeaways

• Monocular cameras capture images from one viewpoint.
• They are useful for recognition, tracking, and visual navigation.
• Estimating absolute distance from a single image generally requires additional information, learned assumptions, or known scale.

How Does a Monocular Camera Work?

Imagine a robot looking at a cardboard box.

Light from the scene passes through the camera's lens and reaches its image sensor.

The sensor produces a digital image.

Computer vision software can examine the image to identify the box and estimate its position in pixel coordinates.

However, the image does not directly provide a unique physical distance.

A small box nearby can occupy approximately the same image area as a larger box farther away.

Additional information is needed to distinguish these possibilities.

How Can a Monocular Camera Estimate Depth?

Several methods are available.

Known object dimensions: If the system knows an object's size, it can use image geometry to estimate distance under suitable conditions.

Camera motion: Images captured from different positions can help estimate three-dimensional structure.

Machine learning: A trained model can predict depth using visual patterns learned from examples.

Additional sensors: Information from LiDAR, IMUs, or other devices can provide scale and improve estimates.

Monocular depth-estimation models can produce useful results, but their accuracy depends on training and operating conditions.

Monocular vs. Stereo Camera

A monocular system uses one camera viewpoint.

A stereo system uses two viewpoints separated by a known distance.

Stereo vision estimates depth by comparing where the same visual features appear in both images.

This can provide geometric depth measurements when the cameras are properly calibrated and corresponding features can be matched.

Monocular systems generally offer simpler hardware, while stereo systems provide additional information for estimating distance.

Why Are Monocular Cameras Useful in Robotics?

Monocular cameras are compact, widely available, and relatively straightforward to integrate.

They can support object detection, visual inspection, and navigation.

A robot may use a monocular camera to recognize a target and another sensor to determine its distance.

The appropriate combination depends on the task.

Frequently Asked Questions

Can one camera be used for SLAM?

Yes. Monocular visual SLAM uses images captured during movement to estimate camera motion and construct maps, although absolute scale can be ambiguous without additional information.

Is a monocular camera the same as an RGB camera?

Not necessarily. Monocular describes the use of one viewpoint. RGB describes the color information captured.

The Bottom Line

Monocular cameras provide useful visual information using a single viewpoint. They are widely used in robotics, although reliable three-dimensional measurement often requires additional estimation methods or sensors.