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The compression option on your digital camera reduces the size of your image files by eliminating some of the picture data. Unfortunately, this feature has a drawback: Any time you eliminate picture data, you also lose a little bit of picture quality.
Most cameras offer a choice of compression settings, each of which removes a bit more data from the file, thereby reducing the amount of memory needed to store the picture file. The compression controls go by different names depending on the camera manufacturer:
- Most cameras assign the name Picture Quality or Quality to the main menu item that controls compression.
- The specific compression settings usually have labels like the following:
• SHQ (super high quality), HQ (high quality), and SQ (standard quality)
• Superfine, Fine, Normal, Basic
• Best, Good, Economy
- On some cameras, the top quality setting is labeled TIFF. When you choose this option, the camera stores the image file in the TIFF file format rather than the standard JPEG format.
Whatever the labels, the camera applies the least compression when you choose the maximum quality setting. This results in the best picture quality but also the largest file size.
Understanding picture file formats
File format refers to a method of structuring data within a computer file. Imaging scientists have developed several formats for storing digital picture data, each of which handles the task slightly differently.
Digital cameras typically rely on the following formats:
- JPEG: The JPEG format (pronounced jay-peg) is the leading digital-camera file format and is also the best format to use for online photo sharing. JPEG applies lossy compression, which eliminates some picture data to reduce the size of the image file. A high degree of JPEG compression results in very low picture quality, but a moderate amount of compression usually is acceptable.
- TIFF: The TIFF format (pronounced tif) applies a form of file compression that retains top picture quality, which, unfortunately, also results in very large picture files. In addition, Web browsers and email programs can't open TIFF files, so you need to make a copy of a TIFF picture in the JPEG format before sharing it online. You can, however, insert a TIFF file directly into a word-processing document, a page-layout program, or other print-publishing program.
- RAW: This format is the only one of the trio that doesn't have an acronym for a name. This format stores picture files without any of the usual color-correction and other adjustments that are done after you press the shutter button. Those in-camera processing steps typically produce a better-looking picture, so unless you're a purist who wants to do that type of correction yourself in a photo editor, stick with JPEG or TIFF. Be aware, also, that most photo editors and other programs can't open RAW files; you need to convert them to JPEG or TIFF first. RAW files also are very large, just like TIFF files.
 | Only some digital cameras offer a format other than JPEG; check your camera manual to find out what options are available on your model. |
How much compression is too much?
Two types of compression exist:
- Lossless compression eliminates only data that isn't essential to maintaining the picture quality. As you can imagine, this type of compression doesn't reduce the file size much.
- Lossy compression is less discriminating in dumping data, sacrificing some picture quality in the name of smaller file sizes.
The file format that the camera uses to store the picture data determines the type of compression that's applied. Most digital cameras store images in the JPEG file format, which applies lossy (destructive) compression. Some cameras also offer the option of storing pictures in the TIFF format, which applies lossless compression.
If you select TIFF, the amount of compression depends on the picture itself — some images contain more noncritical data than others. You don't have any input in the compression decision.
For JPEG images, most cameras enable you to vary the amount of compression. The more compression you apply, the more data that's sacrificed. A highly compressed image produces a small file size but also a low-quality image. The exact amount of compression that's applied at each setting depends on the camera.
 | For most pictures, choosing the JPEG format with a minimum amount of compression offers a good tradeoff between picture quality and file size. Shoot the same image at all the available compression options and compare the results; you may find that you can get away with your camera's second-highest JPEG quality setting. |
 | Be especially careful about applying a high degree of compression (choosing a low picture-quality setting) for pictures that you plan to edit before sharing them online. You will need to resave the pictures in the JPEG format after you edit them, and the images will then undergo another round of destructive compression. Each application of compression does further damage to the picture, so if you start with an image that's already of poor quality, it will only look worse after your editing. (Merely opening and viewing the image doesn't do any harm, however.) |
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