Digital zoom

Digital zoom is a method of decreasing the apparent angle of view of a digital photographic or video image. Digital zoom is accomplished by cropping an image down to a centered area with the same aspect ratio as the original, and usually also interpolating the result back up to the pixel dimensions of the original. It is accomplished electronically, with no adjustment of the camera's optics, and no optical resolution is gained in the process.

When comparing the image quality achieved by digital zoom with image quality achieved by resizing the image in post-processing, there's a difference between cameras that perform potentially lossy image compression like JPEG and those that save images in an always lossless Raw image format. In the former case, digital zoom tends to be superior to enlargement in post-processing, because the camera may apply its interpolation before detail is lost to compression. In the latter case, resizing in post-production yields results equal or superior to digital zoom.

Modest camera phones use only digital zoom and have no optical zoom at all. Usually cameras have an optical zoom lens, but apply digital zoom automatically once its longest optical focal length has been reached. Professional cameras generally do not feature digital zoom.

The optical zoom cameras can be set first before its maximum and then followed by its digital zoom in video mode only, but most of the cameras use the digital zoom after the optical zoom reach the maximum for photo and video. Digital zoom use the center area of the optical image to enlarge the image. By reducing the MP image size, using digital zoom can be done without image deterioration and some cameras has Undeteriorated image mode or at least has Image deterioration indicator.

The table below give Undeteriorated (optical+digital) zoom limit for some MP image size of a certain camera with Optical zoom 24x and Digital zoom 4x for its maximum capability:

Note: These lines are interpolation.

When using digital zoom for photo, the Undeteriorated digital zoom limit is 1.3x, 1.8x and 2.25x respectively for 10MP, 5MP and 3MP, but when using VGA, the image quality is always good under Undeteriorated digital zoom limit, because the digital zoom is only maximum 4x, while the limit is 7.2x, but some cameras with 16MP have digital zoom up to 7.2x or using the capability to the edge for VGA. The table above has also shown that from 3MP jumps directly too much too VGA and this camera has no option of 2MP (1920x1080) and 1.3MP, but other cameras have it.

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Wikipedia