Digital Camera Guide
What Is The Difference Between Optical Zoom and Digital Zoom? Which is Better?
Both optical zoom and digital zoom are means to magnify an image, but they work in
radically different ways and yield radically different results. In general, optical
zoom will always yield a far superior image than digital zoom.
How does optical zoom work?
A digital camera that offers optical zoom works the same way as a zoom lens on
a traditional camera. A traditional lens works by collecting light rays and
projecting them onto a piece of film, or in the case of a digital camera,
onto the sensor. The distance from the lens to the point where all of the light
rays are in focus (focal point) is known as the focal length of the lens.
Unlike a fixed lens, a zoom lens has several moveable glass elements inside. By
adjusting these elements, the focal length of the lens can be changed. Adjusting the
focal length both changes the view distance and reduces the field of view, causing
the projected image to appear larger.
In a digital camera with optical zoom, the same number of pixels are captured
when the image is magnified. The only thing that changes is which rays of light are
projected onto the sensor to form those pixels.
How does digital zoom work?
Unlike optical zoom, digital zoom works by scaling up the pixels in the final image
after it is captured. This is very similar to cropping and resizing your picture in
your favorite paint program, except that the camera does it for you.
Because simply doubling the size of the pixels would create a very "jaggy" or
stair-stepped appearance, manufacturers use different techniques to fill in the
missing pixels. The idea is to come up with a reasonable approximation of what color
that pixel might have been had it been captured. Many algorithms involve looking
at the pixel's nearest neighbors and coming up with some sort of an average; other
algorithms are more sophisticated and take several different factors into account.
While some algorithms are unquestionably better than others, the truth is that
all of these algorithms are still only producing "educated guesses"... they are
not able to determine what color the pixel is in reality. It is for
this reason that digital zoom does not produce as crisp or clear an image as
optical zoom, which has true color values for all of the pixels.
Is there ever a reason to use digital zoom?
Many experts would say "no" as there is nothing that can be achieved with digital
zoom that cannot be achieved after the fact - perhaps even with better results - with
your photo editing software. However, in practical use many beginners still
find digital zoom a nice feature versus no zoom at all.
If you are a novice with your computer, you may find it easier and
more convenient to simply use your camera's digital zoom feature rather than to crop
and resize the image on your PC. In addition, the growing number of docking
stations, stand-alone print devices and photo services that will print directly
from your camera's memory card are making it such that you don't necessarily
have to own a PC to use a digital camera. If your camera doesn't have an
optical zoom feature, then a digital zoom feature may still be useful
in these cases.
Will digital zoom improve in the future?
Maybe, but due to the nature of the differences it seems unlikely that
digital zoom will ever replace optical zoom. Some advanced techniques such as
fractal image restoration have the potential to yield serious improvements over
the digital zoom methods commonly used today. However, general-case algorithms -
especially ones that will work with the limited processing power available
within a camera - still have a way to go before you are likely to see
them widely used in this way.
At this time, optical zoom is the superior choice to digital zoom
when selecting a digital camera.