Tech Features

The computer helper: Deciphering digital camera jargon

By Jay Dougherty Jan 13, 2007, 12:06 GMT

Washington - Digital cameras stem from computers as much as they do from the optical heritage of film cameras.

It's no wonder, then, that today's digital camera users are bombarded with a plethora of acronyms, just as computer users have been for years.

Buy a digital camera, and you'll be confronted with terms such as

RAW, ISO, and noise. What does all of this mean? Read on for some answers.

Q: What's a RAW file?

A: Many digital cameras take images in one of two formats: JPG and RAW. Some cameras even offer the option of recording images in both format simultaneously.

A RAW file records image data directly from the camera's main imaging chip, with little or no internal processing in areas such as contrast, saturation, and sharpness. JPEG files, on the other hand, are the result of a digital camera's internal interpretation of the data it receives from the camera's imaging chip, often called a 'sensor.' JPEG files are also compressed, meaning they have digitally thrown away some of the data that came from the camera's imager, and as a result they're almost always smaller than RAW files.

Just about any graphics viewer or editor can work with JPEG files. RAW files, on the other hand, often require the software that came with your camera. Many enthusiasts and pros prefer RAW files because they want to be the ones who enhance the file in software.

Q: What is ISO?

A: ISO is a term that the digital camera makers borrowed from the film industry to describe how sensitive a camera's sensor is to light. Short for Internatianal Standards Organisation, ISO levels on today's digital cameras typically range from values of 100 to 1600, with the lower numbers representing less light sensitivity.

When your camera's sensor is more sensitive to light, it can be used in lower light situations, such as indoors. Brightly lit situations require less sensitivity to light, so lower ISO settings can be used.

Your camera's internal metreing system, which ensures properly exposed images, works in conjunction with the ISO setting of your camera to control how long the camera's shutter must remain open to obtain a well lit image. If your ISO setting is too low for the light level available, your camera's metre will force the shutter to remain open longer to let more light in, and you'll have to hold the camera very steady - or have it on a tripod - in order to get a shake-free image.

For outdoor photography, ISO settings of 100 - 400 are appropriate. For indoor photography, settings of 400 - 1600 are preferred.

Generally you want to use the lowest ISO setting possible in a given light situation in order to avoid digital noise.

Q: What is digital noise?

A: When a digital camera has to boost its sensitivity to light in order to record an image properly, digital noise occurs. Digital noise manifests itself through tiny red and blue dots in an image - often more perceptible in large areas of uniform colour, such as the sky or ocean.

Analogous to digital noise would be the hiss you hear in audio sources when you need to turn up the sound in order to hear a weak signal. Digital noise can also be akin to film grain in photographic prints from film cameras.

At lower ISO settings, generally in the range of 100 - 200, digital noise is almost nonexistent. As you increase the ISO of your digital camera, digital noise becomes more apparent. Noise will be so apparent at ISO settings above 800 that some camera users feel pictures taken at these higher ISO levels are unusable.

--- Have a computer question? Send it to the Computer Helper at jayd@csi.com.