digital zoom

A feature of digital cameras and digital camcorders that tries to reproduce the effect of a zoom lens electronically.
In some conditions this yelds good results, but in most cases it produces a blotchy pixelated image.

For example, if you are using a digital camera with a 2048 x 1536 CCD, you can use only the central 640 x 480 portion and get something like a 10x digital zoom. But of course, then you are left with a 640 x 480 image; you can either live with it, or digitally interpolate the picture to a higher resolution - and this is when the blotchyness appears.

Digital Zoom

Most digital cameras nowadays have a digital zoom in addition to (or, in some cases, in stead of) an optical zoom.

The optical zoom works like any other zoom would: The glass (or in some cases, plastic) in the lens bends the light onto the CCD, so whatever you are taking a picture of appears closer.

A digital zoom works quite differently. Instead of doing anything with the light that comes into the camera, a digital zoom is a software implemetation that occurs after the image is taken into the ccd chip.

To get a digital zoom, the digital camera takes the picture as normal, but discards the information along the edge of the camera:

+----------------------------------------+
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|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
|XXXX+------------------------------+XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX|                              |XXXX|
|XXXX+------------------------------+XXXX|
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
+----------------------------------------+

If the camera discards half of the pixels from the ccd (i.e only uses the centre half of the pixels), you have a 2x digital zoom.

There are two ways digital zoom can be implemented:

1) The camera discards the outer half of the pixels, and stores the remaining pixels to the flash memory, thus cutting storage requirements in two.
2) The camera discards the outer half of the pixels, and then interpolates the remaining pixels so the final image has the same resolution as a non-digital zoomed picture would have.

Advantages with digital zoom:

• You can impress your friends by saying "Look at the awesome zoom on this camera!"
• It can help you focussing manually when doing macro photography work

Disadvantages with digital zoom:

• If your camera interpolates the image, it's a waste of storage space and battery capacity - you could as well have resized the image in Photoshop or any other image editing program.
• You might as well just take the picture normally, and then crop and resize it in your favorite image editing program

The bottom line: Digital zoom - just don't bother.

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