How is a digital camera different from a film camera? What are pixels and why are they important? What's the difference between optical and digital zoom? What advantages do digital cameras have compared to film cameras? Let's address these and other questions as we discuss digital camera technology.



First a short history and overview of digital imaging…

The technology began with television in the early 1950's when researchers discovered how to convert video images to electrical signals for storage on magnetic tape. In the 1970's electronic still photo cameras were developed. These employed the first generations of solid-state image sensors. By the late 1980's megapixel sensors were introduced - the technology that paved the way to today's modern digital cameras.

Fundamentally, film and digital cameras do the same thing. Both utilize camera lenses to focus photographic images on a light sensitive medium where they are stored for later retrieval. But the way each camera does this is radically different.

Instead of capturing the image on film that must be developed and printed, digital cameras measure light and color characteristics using photodiodes built into a sensor - either a Charged Coupled Device (CCD) or Complementary Metal-Oxide Semiconductor (CMOS). An Analog-to-Digital Converter (ADC) then converts the signal to binary, or digital, code. This code is sent to a Digital Signal Processor (DSP) which adjusts photographic elements such as contrast and color, and compresses the file for storage in the camera's memory, compact flash card, or other memory device.

Digital cameras have huge advantages when it comes to viewing and printing photos. It's nearly instantaneous! We can immediately look at the picture on the camera's LED screen, and if we don't like it, delete it and shoot again. Or we download and view it on our computer's monitor. And the pictures can be cropped or enhanced in minutes on the computer with photo software and printed with a photo printer. Plus many digital cameras have optional printer docks that don't require a computer at all.

What's a Pixel?

The human eye perceives a nearly infinite blending of light and color which high-quality film can approximate in a photograph. A digital image however, is a binary code file that records these variations as elements called pixels - short for picture elements.

Pixels are tiny squares of light and color, that when assembled create a mosaic. And like a mosaic, if the squares are small enough we see a smooth, photographic image. However, if the pixels are too big the transitions appear jagged or out of focus.

More pixels equal higher resolution and photos with clearer sharper detail, much like when you look at a mosaic with very small elements. For example, a 3 Megapixel digital camera can produce pretty good snapshots and even enlargements to about 8” X 10”. But the more you enlarge, crop or otherwise manipulate the image, the larger the pixels become, degrading the photo's quality.

Does size matter?

The number of pixels the sensor produces is important, but so is the quality. The CCD sensors of many small digital cameras are about the size of a small fingernail, while some larger models will feature sensors up to about 1” across. There are conflicting opinions about sensor type and size, and the technology is advancing. But in general it can be argued that the photodiodes in a tiny CCD probably won't be as powerful or effective as an equal number in a larger sensor.

So unless your most important considerations are the smallest and/or cheapest camera, you're likely to be happier with the picture quality from a slightly larger model, assuming both have the same number of pixels.

All Zooms are not equal

The specs say the camera has 3X optical and 4X digital for a 12X total zoom. Sounds good, right? The answer is yes and no. Optical zoom works like a telescope, while digital zoom crops the picture. Using these zoom specs with our 3 megapixel camera example, here's what happens.

Optical zoom brings the image 3X closer and uses all 3 million pixels. But digital zoom crops up to 75% of what the lens sees and the sensor is exposed to, so the photo now has about 750,000 pixels. Depending on lighting and other conditions, using full digital zoom may not even get you a good 4” X 6” print.

The Future of Digital Photography

The last few years have seen tremendous advancement in digital imaging technology. Some high-end digital cameras can now generate more than 12 million pixels and produce photos that rival medium-format film cameras. As with all electronic technology, it's reasonable to expect even better cameras will come to the market over the next several years.

Photography “purists” will probably resist abandoning their film cameras as long as possible. But when comparing convenience, flexibility and quality, it seems inevitable that the majority of photographers will opt for digital over film photography – and probably sooner rather than later.