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Digital Photography Success
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Digital Zoom vs Optical Zoom
Perhaps the most misleading of all features advertised for digital cameras is the digital zoom range. Manufacturers realize that consumers
will try to compare digital cameras on the basis of features that have a number attached. This is expected considering that most novice
buyers don't know what to look for, let along what many of the features mean. The most common comparison points for buyers besides
price are probably: the number of megapixels (resolution) and zoom range. Unfortunately, too many people get conned into comparing the
heavily advertised digital zoom, and ignore the important one: optical zoom.
Digital Zoom
Typically only found on digital point and shoot cameras, digital zoom is an attempt to increase a camera's zoom range beyond what the
lens is capable of through optical magnification alone. Digital zoom can reduce the quality of the resulting image, and as digital SLR
cameras generally strive for optimum quality over ease of use, such a feature is rarely included in these cameras.
At a more detailed level, most digital SLR cameras do not include any digital zoom because an assumption is made that digital SLR users
don't want their camera to do any post-processing. Digital zoom is just another type of post-processing, and any in-camera processing will
be of lesser quality and flexibility than what can be achieved in software on your home computer. For this reason, it is best to leave these
operations to full-featured computer software, rather than having the camera guess at the appropriate settings and algorithms to use.
What is digital zoom?
Digital zoom is simply a software program running in your camera that enlarges your original image (as if you were zooming in with a real
optical zoom lens). The resolution of the digital sensor is fixed and no more image information exists to help create this "zoomed in"
simulation. Therefore, the software must attempt to make an educated guess at what the additional pixels might look like. This process is
called interpolation, and is the act of estimating what data might exist between any points of known data.
For example, let's say that your camera has 2.0x digital zoom. When the camera is set at 1.0x digital zoom, the camera is capturing exactly
what it sees with its sensor array through the lens (ie. the digital zoom is disabled). But if one were to increase the zoom to 1.5x digital,
then we are basically inserting an extra pixel for every two real pixels. Many algorithms exist for this interpolation, but they all generally
involve averaging the contents of the known pixels surrounding the unknown / new pixel.
The amount of digital zoom is often quoted as the product of the real optical zoom and the amount of digital magnification. In other words, a
camera that advertises 3x optical and 6x digital zoom is really 3x optical with an additional 2x magnification simulated through digital
enlargement.
As would be expected, the digital "zoomed" version of a photo will generally show less detail and not be as sharp. This is because what
used to be a sharp edge (eg. a bright line in the photo) would now be blended across multiple pixels. Advanced digital zoom algorithms
might try to compensate for this by adding in sharpening and edge detection. Even with these additional methods, the camera is only
making educated guesses about the content for the new pixels and cannot obviously add any new detail to the original image.
Optical Zoom
Optical zoom is the visual magnification we were all familiar with prior to the advent of digital cameras. A set of moving lenses allows a
range in optical magnification that runs anywhere from 2.0x to 10.0x. The ultra-compact digital cameras either offer no optical zoom (easily
spotted by no protruding / moveable lens element), or they may go so far as to provide up to 3x optical zoom. Prosumer digital point and
shoot cameras with the ultra-zoom lenses sometimes provide zoom range up to 10x. Most people will find that 3x optical zoom is an
absolute minimum requirement for their digital camera.
Disable Digital Zoom
Many digital cameras have designed their zoom function to automatically switch over from optical zoom to digital zoom once the optical
range is at maximum. Usually, the camera will indicate on the LCD display that it is now using digital zoom instead of just optical zoom. If
image quality is important to you, make sure that you never exceed the optical zoom range and enter the digital zoom range. Most cameras
provide some means of disabling digital zoom, which would prevent you from zooming past the real zoom range. I strongly recommend that
you find this option and disable it, preventing accidental use of the digital zoom feature.
If you need to enlarge part of a digital photo, leave it up to software such as Photoshop, where you will have much better control over how
the enlargement is done (eg. using bicubic smoother, etc.)