Lossless zoom

In a network video stream, you use digital zoom to magnify a specific part of a view area. The zoom–in is scaled to the output resolution. This scaling process might cause interpolation and pixelation which leads to a loss of image quality.

With lossless zoom, you can zoom in more without losing image quality, hence, keeping all details in the image as sharp and clear as they were before you zoomed in.

Output resolution significantly impacts image quality. Lossless zoom is effective when the output resolution is less than or equal to the view area resolution. This white paper explains the concept of lossless zoom, how it functions in panoramic multisensor cameras, and the key differences between lossless zoom, lossy zoom, and optical zoom.

Panoramic multisensor cameras have digital PTZ (pan-tilt-zoom), a feature that allows users to pan, tilt, and zoom within a video stream without the need for a motorized camera. Digital PTZ allows you to zoom in and explore a video stream digitally, however, digital zoom can result in a loss of image quality.

Lossless zoom is a type of digital zoom that is particularly more effective in high resolution cameras. High resolutions capture detailed video stream that can be resized and downscaled for display without compromising image quality.

Panoramic multisensor cameras use multiple sensors to provide a single, wide-angle panoramic view. A high-resolution panoramic camera can have multiple view areas and within each view area, you can digitally pan, tilt, and zoom. For more information, see the white paper on Panoramic cameras .

Digital zoom allows users to zoom in on a specific part of a view area, while producing high resolution images. However, digital zoom can cause a loss of image quality due to interpolation and pixelation. When zooming in on a specific part of a view area, the panoramic camera captures the image using the sensor’s full resolution and scales the image to the output resolution. An interpolation process occurs, where the camera has fewer pixels to produce the image, meaning that the view area resolution has become lower than the output resolution. It creates new pixels for the image which results in a pixelated image, also referred to as a blurry image, characterized by loss of sharpness. As you zoom in further with digital zoom, the image becomes increasingly blurry.

The invention and evolution of digital zoom has evolved from having lossy zoom to having both lossy and lossless zoom.

Lossless zoom allows you to zoom in on a specific part of the view area without compromising image quality. For example, a high resolution camera has more pixels than required for streaming. When zooming in, the view area uses pixels from the source resolution and as the zoom continues, the available pixels decreases until lossless zoom is no longer possible. Then, it becomes lossy zoom.

The level of zoom that is possible without loss of image quality is determined by the output resolution in comparison to the view area resolution. Depending on the display monitor, web browsers might downscale or upscale images by default, impacting overall image quality. Zooming in on an image could fall within any of these three scenarios; downscaling, no scaling, or upscaling:

• Downscaling: Downscaling occurs when the output resolution is lower than the view area resolution. For example, the requested output resolution could be 4096 x 1024 from a view area resolution of 10240 x 2560. As you zoom in further, lossless zoom stays effective until the output resolution becomes the same as the view area resolution which then leads to the no scaling scenario.

• No scaling: In this scenario, the output resolution is the same as the view area resolution and there is no scaling. At this point, zooming in will lead to an upscaling scenario.

• Upscaling: The output resolution is higher than the view area resolution and lossless zoom is no longer possible. Digital zoom has switched from lossless zoom to lossy zoom.

There are certain differences between optical zoom, lossy zoom, and lossless zoom:

These are images from a 26 megapixels Axis panoramic multisensor camera when the output resolution (3840 x 2160) is less than the view area resolution (10240 x 2560). The right image shows when digital zoom is in lossy mode.