CNET editors' digital SLR buying guide: All about image files

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What you need to know, from the kind of user you are to current technologies.

All about image files

Most standard digicams capture pictures in JPEG format only, but digital SLRs give you more choices. Here's a rundown of three important file formats:

JPEG

A lossy, compressed file format. Lossy means that actual image data is discarded to increase the compression ratio.
Pros:

Can achieve very large reductions in file size; the resulting smaller files take up less drive and media space and transmit much faster.
Almost universally supported by imaging programs such as browsers. Sorting, viewing, and cataloging are quick and easy.

Cons:

Produces artifacts and causes loss of detail that may be difficult to notice at low compression ratios but gets progressively worse as compression increases.
JPEGs are finished RGB images, meaning you have limited ability to alter or reverse the effects of in-camera settings such as white balance, tone curve, or sharpening.

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TIFF

An uncompressed, finished RGB file format.
Pros:

No quality loss.
Almost universally supported by imaging programs.

Cons:

Files are many times larger than even low-compression JPEGs.
TIFFs are finished RGB images, meaning you have limited ability to alter or reverse the effects of in-camera settings such as white balance, tone curve, or sharpening.

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Raw

The photographer's power tool--it's hard to overemphasize just how powerful they are. Raw files are minimally processed data from the sensor, which you convert to finished RGB images using special software on your computer.
Pros:

Highest potential image quality.
Depending on your raw-conversion program, you can make extensive changes to image parameters such as exposure, white balance, tone curve, and sharpening.
Typically about one-third the size of an RGB TIFF but with none of the information loss of a JPEG.

Cons:

Images are unfinished, so they need to be converted to another format for printing and posting on the Web, which is often a time-consuming process.
Raw formats are proprietary and usually camera-specific and are often not supported by image editors and other software.

Hint: Think twice about any digital SLR that is not supported by a good raw-conversion program. If the camera's manufacturer doesn't make a decent converter, look for a third-party application. We've counted at least half a dozen for various digital SLR models. And many image-editing apps now include good raw-conversion features for a wide range of popular digital SLRs.

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About colors

The ability to specify your image's color space is a common feature on digital SLRs. What's a color space? In this case, it's a defined range of available colors. The larger the range, the greater the color fidelity and richness your images have. Typically, you can choose between the two color spaces known as sRGB and Adobe RGB. sRGB corresponds well to the set of colors that a typical computer monitor can display. Adobe RGB includes more colors and is a better match for the range of hues produced by the offset printing machinery that is used to make magazines, brochures, posters, and the like.

Some digital SLRs include additional color modes or "looks," which offer different levels of color saturation, color emphasis, and contrast--similar to the varying looks of different films. If you shoot JPEGs and don't have time for a lot of Photoshop tweaking, these color modes can be a handy shortcut to getting the results you like. Most digital SLRs also allow you to create custom color modes by adjusting each of the parameters independently and saving them as a set.

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