Tech Focus: Digital Zoom vs. Optical Zoom

There has been a surge in demand for high-quality imaging solutions across many industries, from medical applications to UAVs, and everything in between. For most of these solutions, flexible and responsive zoom options are often critical.

When selecting a camera for your application, you will probably see the optical zoom and/or digital zoom capabilities of the camera listed in the specification (often both). But what do these actually mean, and how do they impact your choice?

Optical zoom offers greater resolution than digital zoom but is limited by the quality of the physical optics of the camera lens. Digital zoom enlarges an image using digital processing but generally results in a lower image quality.

Optical zoom: preserving image quality

Optical zoom functions by adjusting the physical focal length of the lens, thereby magnifying the image without sacrificing quality. To zoom in, the lens moves, narrowing the field of view and magnifying the scene. Optical zoom captures more detail by actually bringing the subject closer optically, unlike digital zoom, which relies on digital manipulation. This results in sharper, clearer images with no loss of resolution.

Optical zoom is particularly beneficial in scenarios where image quality is paramount, such as surveillance applications, requiring detailed identification, and industrial inspection, where precision is critical to guarantee quality. By preserving the integrity of the image, optical zoom ensures that users can accurately capture finer details even at a high distance.

One drawback of optical zoom is that, as the image is magnified, the amount of light received by the sensor is reduced. The Automatic Exposure in modern cameras can usually compensate very well for this (by changing gain, shutter speed and iris settings) but it may be an issue with darker scenes and cheaper low sensitivity sensors.

Digital zoom: enhancing pixels digitally

Unlike optical zoom, which adjusts the lens physically to magnify the image, digital zoom works by digitally enlarging and cropping a portion of the image. Essentially, it increases the magnification of the image by interpolation (estimating a new pixel’s intensity based on neighboring pixel values). This estimation results in lower image quality and less detail than with optical zoom.

Since it merely enlarges the image using the existing pixels, without capturing additional detail, digital zoom is best suited for situations where high-resolution images are not essential, where immediate magnification is required but precise detail may not be critical.

However, recent developments in software have enhanced digital zoom capabilities and more sophisticated algorithms mean that interpolation is more accurate. Digital zoom is also less of a problem if the camera image is downscaled from an image captured using a very high resolution sensor. In this case, when the image is digitally zoomed increased levels of detail can be obtained from the higher resolution image captured by the sensor.

Applications of digital zoom vs. optical zoom

The choice between using digital zoom or optical zoom ultimately depends on the specific requirements of the application.

Digital zoom is well-suited for situations where immediate magnification is necessary, and image quality can be sacrificed to some extent. These include video conferencing, and real-time monitoring systems such as patient monitoring, where reactive zoom capabilities are valued over image clarity. Zooming in on a specific region of the field of view will result in pixelation, particularly if there is a significant amount of digital magnification.

Furthermore, digital zoom can struggle in low-light conditions. This is because digitally magnifying a poor, low-light image just makes the reduced quality more visible.

While this may also be an issue with optical zoom, with digital zoom a bad image (with low detail due to low light) is just being made bigger so it looks worse, even though no additional noise is added. With optical zoom the camera can compensate to some extent by adjusting iris and shutter speed settings to capture more detail.

Optical zoom is usually preferred in applications where image quality is imperative and detailed visualization is essential. This includes professional surveillance systems requiring precise identification, and industrial inspections where capturing fine details is crucial for analysis and decision-making. Optical zoom is also a better choice for applications that require reliable performance in low light or changing light conditions.

Limitations of optical zoom

An optical zoom will not be suitable for every application. Consider these limitations when selecting your camera:

Size and weight: due to the requirement to motorize the position of certain lens elements, optical zoom lenses are typically larger and heavier than the fixed lenses used with digital zoom. Therefore, optical zoom lenses may be less suited to embedded applications which require compact, lightweight hardware.

Fixed central zoom field: Optical zoom narrows the field of view (FOV) of the lens system, and only zooms in and out of the center of the field of view. If better precision is needed in portions of the peripheral FOV, then a separate pan and tilt system are also required to change the orientation of the entire camera. A digital zoom can be applied to any region of the camera view, and both views can be displayed simultaneously.

Cost and complexity: Optical zoom lenses often cost more than their fixed counterparts, because they include moveable optics and a motorized system to allow control of the optical zoom.

Harrier AF-Zoom cameras

While both digital zoom and optical zoom serve the purpose of magnifying images, they differ significantly in terms of image quality and application suitability.

Our Harrier autofocus-zoom cameras all incorporate a lens system for optical zoom and image processing for digital zoom, allowing users to adjust magnification both optically and digitally.

Harrier AF-Zoom Cameras achieve their powerful zoom using a hybrid optical system. This means that the camera first uses optical zoom to magnify the image without sacrificing quality. Once the optical zoom limit is reached, the camera can then switch to digital zoom to further increase magnification, although some loss in image quality may occur.

Our most powerful model, the Harrier 55x AF-Zoom Camera, is slightly different because it uses a higher resolution sensor, so the initial digital zoom is merely reducing the downscaling to the point where the zoomed image can be directly cropped out of the higher resolution image.

All our cameras, including Harrier, Tamron and Sony models, are compatible with our Harrier Camera Interface Boards to increase the output options of the cameras. We therefore offer 10x to 55x optical zoom cameras with LVDS, 3G-SDI, USB3, HDMI and Ethernet IP video outputs. All these cameras also include a digital zoom capability; find more information in the product listings.

Take a look at the full range and get in touch to see which Harrier AF-Zoom Camera is best suited to your vision system.