Digital zoom is a method of decreasing the precise angle of view of a digital photograph or video image. It is accomplished by cropping an image down to an area with the same aspect ratio as the original, and scaling the image up to the dimensions of the original. The camera's optics are not adjusted. It is accomplished electronically, so no optical resolution is gained.
In cameras that perform lossy compression, digital zoom is preferred to enlargement in post-processing, as the zooming may be applied before detail is lost to compression. In cameras that save in a lossless format, resizing in post-production yields results equal or superior to digital zoom.
Lower-end camera phones use only digital zoom and do not have optical zoom, while many higher-end phones have additional rear cameras, including fixed telephoto lenses that allow for the simulation of optical zoom. Full-sized cameras generally have an optical zoom lens, but some apply digital zoom automatically once the longest optical focal length possible has been reached. Professional cameras generally do not feature digital zoom.
Digital zoom is implemented in one of two ways:
- Cropping - the software crops the image so that the subject would appear bigger on the screen of the phone but the resulting image is smaller than the maximum resolution of the camera. The photo of the subject does not have any more detail than a non-cropped photo would.
- Stretching - this is similar to cropping but instead it stretches the cropped photo to the selected resolution. Since the stretching is done by an algorithm that uses just the information from the cropped photo no additional detail is visible.