Taking a digital photograph means recording data for millions of pixels that form the image -- and while digital cameras and contemporary memory cards elegantly handle this storage -- the resulting files can be quite large in size, inconvenient to store, share or post to the Internet. The JPEG file compression standard, introduced in 1992 by the Joint Photographic Experts Group, is commonly used to reduce images to a reasonable file size, while maintaining high quality. Things can go wrong, however, and these files can be corrupted, resulting in damaged or lost images.
Understanding Image Compression
The JPEG format uses complex algorithms that discard image data that has minimal impact on how the human eye sees a photo. It also uses data storage shorthand to encode information that repeats in a photo, such as large areas of a single color. Data that is discarded is lost. Despite this loss of image information, compressed images using this format produce files that are a fraction of the size of the original with high photographic quality.
How Data Corruption Occurs
Storage media can cause data corruption, through events such as bad sectors developing on aging hard drives, scratches on CD or DVD surfaces or failed transistors on memory cards. Transferring files between the camera and computer, or moving files between folders, may introduce errors as well. Because of the compression used in JPEG files, minor data corruption can have a major impact on the image, unlike lossless compressed files or uncompressed images, where file corruption can affect smaller portions of the complete image.
Recovering JPEGs With Utilities
Repairing corrupt JPEG files is tricky, since data is missing from the file even before corruption occurs. For a utility that performs well, much of the repair process depends on what data is lost through corruption. In 2012, website TechRadar tested JPEG repair tools for a variety of file corruptions. Picture Doctor 2.0 had an image recovery rate of 64.3 percent, followed by Stellar Phoenix JPEG Repair 188.8.131.52, at 62.5 percent. In third place, PixRecovery 3.0 scored 51.8 percent (see links in Resources).
Re-Creating JPEGs From Source Material
Re-creating a JPEG image has a better chance of success than a repair. In the case of scanners, if you have the means to re-scan an original, creating a new JPEG is your best option. Some digital cameras allow you to save files in multiple formats simultaneously, such as JPEG and the camera's native RAW format. If you save the RAW images, you can create new JPEGs as well, converting within your camera maker's software or image editing program.
- Why Do Math: Image Compression -- How Math Led to the JPEG2000 Standard
- Microsoft: Windows: Understanding Picture File Types
- File Format Info: Corruption of Graphics Files
- TechRadar: Recover Lost Photos -- How to Repair Corrupt Images
- SoftOrbits: Picture Doctor
- Stellar Data Recovery: Stellar Phoenix JPEG Repair
- Office Recovery: PixRecovery