Digital Compression of Image Files

Digital compression uses complicated algorithms and mathematical formulas to compress digital images. In fact, digital cameras digitally compress files as a standard part of data storage in order to consume less memory.

As the name suggests, compression reduces the size of the files so that a camera can hold more data for other files. However, because some forms of digital compression alter the original image, be sure to know the compression method before saving data to a file.

How Digital Compression Works
Digital compression uses two techniques to compress an image file. The first step is to remove repetitious colors. For instance, a sunset will have large areas where the colors are the same. Although the compressed file removes these repeated colors, it can reconstruct them when the file is expanded.

Secondly, digital cameras capture images that contain more information than the human eye can process. Some of that information can be removed from the image during the compression process without noticeable image degradation.

Digital Compression in Digital Cameras
Digital cameras compress digital files to conserve memory space. Without digital compression, both internal and external memory cards would fill up very quickly. The type of format used when compressing digital files varies, depending on the make and quality of the digital camera.

Some cameras allow the photographer to choose what type of file to use to store pictures. For example, if the exact image is crucial, then the photographer is likely to save the picture as a TIFF file. Conversely, if the photographer wants to load more pictures on his camera, he’ll save his pictures as JPEG files.

Reasons to Compress Images
Saving storage space is the main reason to compress digital files, whether the images are stored in the digital camera, on a hard drive or in other storage formats.

The amount of space that a photographer saves through data compression depends on the file type he chooses. For instance, because compressing digital files into JPEG format creates much smaller files than PNG format, a photographer will open up more space on his camera’s memory by choosing the JPEG file type. JPEG is generally held as the standard when compressing digital files to send as email attachments or for websites.

However, the small size of JPEG files comes at a price. JPEG files are “lossy” files. Every time the image is modified and saved, the compression system loses a little more detail. Although the initial detail loss is not noticeable, the repeated compression of JPEG files has a cumulative effect that eventually ruins the image.

For this reason, lossless compression files are preferred for archiving digital images or creating exact replicas of the original subject. A lossless file does not deteriorate every time it’s saved. Popular lossless file types include TIF and PNG formats.

While lossless files are the preferred digital compression tools for long-term archiving of images, they take up significantly more space than JPEGs. In fact, even compressed lossless files can be as large as the uncompressed file. The tradeoff is size versus quality: although lossless digital compression consumes more memory, the image quality and durability are much better than those of compressed files as JPEGs.

Keep in mind that once images are downloaded onto computers from digital cameras, the photographer has to decide which type of digital compression to use. Most often, compressing digital files is part of the software editing program’s job.

Digital Compression Settings
The average photographer may not be too concerned about the choices available when compressing digital files. Learning to change the compression settings on his or her digital camera, however, is quite important.

You won’t find file types listed in most digital camera compression settings. To find the type of file the camera used when compressing digital files, you’ll probably have to check the instruction manual for your camera.

Instead, the usual settings for digital compression are listed as either “Good, Better, Best,” or sometimes “Normal, Fine, Superfine.” For example, “good” and “normal” take up less space but will produce inferior pictures. Conversely, “best” and “superfine” will take up more space in order to produce better quality pictures.

Consult the following table to see the ratio of the compressed file to the original file. These vary from camera to camera, so these ratios are only approximate.

For the amateur photographer, “better” or “fine” settings are a good balance between photo quality and file compression. Professionals tend to use “best” or “superfine” to get the best quality pictures. Because these settings take up more memory space, professional photographers tend to carry extra memory cards with them to compensate for the lower rate of digital compression.