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photography - digital or optical zoom

Updated on July 14, 2010

Most digital cameras offer both digital and optical zoom features, but what is the difference? It is really important to understand these two very different zooms as they will have a direct impact on the quality of your final pictures.

At the back of the digital camera is a sensor that collects the image as a fine series of dots and stores these in the camera's memory. If the sensor had 1920 x 1200 dots it would be a 2.3 megaPixel camera, a 3840 x 2400 sensor would be a 9.2 MegaPixel camera.

When you zoom in with the optical zoom you are framing the image you want onto all the available dots of the sensor and retaining maximum quality. That is a good thing.

When you then do a 2x digital zoom the camera has to cheat. It takes the central portion of the image the sensor has collected and expands those dots across the whole image area. If your camera is the 9.2MPixel camera mentioned above then the 2x digital zoom will take a 1920x1200 area from the middle of the sensor and blow it up to 3840 x 2400.

The trouble is that in doing that it has to move the dots it has apart and then 'guess' what color the other dots should be. With a 2x digital zoom only 1 in 4 of the dots that make up the picture are from the original image you saw through the view finder or on the screen. The rest are invented by the camera's built in logic.

If you have a 4x digital zoom then each side of your image is expanded by 4x; the total expansion is 4x4 so only 1 in 16 dots of the image are original and the other 15 in 16 are made up by the camera.

2x digital zoom
2x digital zoom

A 2x digital zoom doubles the length of each side of the image. So taking the four pixels at the top and applying 2x digital zoom, the camera produces the matrix below and then has to guess the color of the intermetiate pixels. This is called interpolation and some cameras do it much better than others.

This example would be easy as all the pixels are the same color but suppose they werered, orange, yellow and blue.

This process is simply scaled up for the number of pictures your camera can handle.

The bottom line is that optical zoom is a much better option than digital zoom if the final quality of the image is important, especially if the final image will be enlarger.


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