Different photography file formats on DSLRs and computers apply different levels of compression. Advanced photographers tend to try to avoid compression by shooting RAW files, which have no compression at all applied to them.
It is useful to understand the two different types of compression, so that we can understand the effect they have on files. Read on to answer the question: What is compression?
- Lossless Compression. This is similar to creating a ZIP file on a computer. Data is compressed to make it smaller, but no quality is lost when the file is extracted and opened at full size. It will be identical to the original image. TIFF is the most commonly used file format that uses lossless compression.
- Lossy Compression. This sort of compression works by discarding information, and the amount of compression applied can be chosen by the photographer. JPEG is the most commonly used file format for lossy compression, and it allows photographers to save space on memory cards or to produce files suitable for e-mailing (for example). However, it should be noted that each time you open, modify, and then re-save a "lossy" file, a little bit more detail is lost.
How Digital Compression Actually Works
Digital compression is a twofold process. First, a digital sensor is capable of capturing far more information than the human eye can actually process. Therefore, some of this information can be removed during compression without the viewer actually noticing!
Second, the compression mechanism will look for any large areas of repetitive color, and will remove some of the repeated areas. They will then be reconstructed into the image when the file is expanded.