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Front Page » July 3, 2007 » Tech Tips » The mystery behind digital zoom
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The mystery behind digital zoom

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Sun Advocate/Progress Network Administrator

Optical and Digital Zooms are certainly not created equal

Digital cameras are more than common these days and are especially popular among younger generations. They're convenient, fast and easier than ever to use. Unfortunately, most people still have misconceptions about digital cameras, especially digital zoom.

Many digital camera seekers will see advertisements on cameras for high digital zooms and make the false assumption that digital zoom must be some sort of high tech zoom that only comes with digital cameras.

You can't blame consumers for thinking that way. Anything "digital" is always marketed as a technological advancement. From watches to music, any item labeled "digital" is perceived as more sophisticated than the alternatives.

Sadly, most digital camera manufacturers use this perception to make their product seem better than it really is.

For example, a common tactic used by most manufacturers is to multiply the optical and digital zooms to provide a total or overall zoom. Suppose the camera has a 3x optical zoom and a 10x digital zoom. The manufacturer will claim the camera has an effective 30x zoom.

This is a far, far stretch from the truth, however, as a digital zoom isn't really a "real" zoom. The phrase "digital zoom" is very, very misleading.

In fact, the digital "zoom" supplements the optical zoom after the camera has zoomed as far as the optical lenses will go.

To illustrate the point, suppose an outdoorsman spots a young buck in the shrubs. He pulls out his point-and-shoot digital camera and the lenses zoom in as far as they will go

But the deer is still small in the viewing area, and the outdoorsman wants to zoom in on the buck's head and antlers.

So he presses the zoom button another couple of times, invoking the digital zoom, and then presses the shutter button to take the picture.

The actual image the camera captures is of the entire deer. Software on the camera then crops the image down to the head and antlers to match what the outdoorsman is seeing on the LCD display on the camera.

The software then "blows up" the image to the previous size. See the illustration below for a more visual explanation.

In the end, the image quality suffers from clarity and pixelation (as a result of the interpolation & enlargement process).

Step 1. The camera's optical zoom is fully utilized and cannot make the image any larger.

The camera's shutter captures the image at this size, regardless that the outdoorsman wanted just the deer's head and antlers.

Once the image has been captured by the camera's image sensor it then passes to software which performs the digital "zoom".

Step 2. The digital "zoom" software first crops the image to match the same viewing area that is visible on the camera's LCD screen.

The stronger the digital zoom, the more that is cropped from the original image.

In this case, the outdoorsman wants just the head and antlers, which is what he sees on his camera's screen.

Step 3. The camera then enlarges the cropped image to match the size of the original image before it was cropped.

It does this by using a process called interpolation, where the camera intelligently "guesses" what pixels need to be added.

In all reality, this whole process is much like using the zoom tool in your computer's image viewing software.

(Photos slightly exaggerated to illustrate the digital zoom process)

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