Understanding Compression in Digital Photography

Why Photographers Need to Concern Themselves with Image Compresssion

Compression in digital photography
A professional photographer is more likely to shoot in the RAW image format, which involves no compression, than JPEG. PeopleImages / Getty Images
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Compression is a big issue when it comes to photographs and it is very easy to ruin a great image by compressing it too much and too often. It is important to understand compression in digital photography, so you can control it properly to meet the needs of a particular photograph.

What is Compression?

Compression is used to reduce the size of any file on a computer, including image files. Files are compressed to reduce their size and make them easier to share on the web.

However, when it comes to photographs, compression is not always a good thing. 

Different photography file formats on DSLR cameras and computers apply different levels of compression. When an image is compressed (in the camera or the computer) there is less information in the file and the finer details of color, contrast, and sharpness are reduced.

With a compression format such as that found in a JPEG file, you will be able to fit more files onto the camera's memory card, but you are also sacrificing quality. Advanced photographers try to avoid compression by shooting RAW files, which have no compression applied to them. However, for general photography, the compression found in JPEG is not a significant drawback.

Noticing Compression

The difference in compression formats may not be noticeable on the camera's LCD screen or even a computer monitor. It will be most evident when printing an image and will play a greater role if you intend for that image to be enlarged.

Even the quality of an 8x10 print can be impacted by too much compression. But if you're just sharing a photo on social media, a loss of quality through compression should not affect you enough to be noticeable.

Digital photography has progressed greatly in recent years. Many photographers want the latest camera with the most megapixels and will continually upgrade.

However, if that same photographer does not pay attention to compression from the time an image is captured through post-production and storage, then they have simply wasted the extra quality that they paid for.

How Digital Compression Actually Works

Digital compression is a two-fold 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.

The Two Types of Image Compression

It is useful to understand the two different types of compression so we can understand the effect they have on files. 

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 or posting online. 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. 

Tips for Avoiding Compression Issues

There are steps that any photographer can take to avoid losing the quality of their photographs to compression.

  • Shoot in RAW if your camera allows you to. If file size and storage capacity is an issue for  you, get cards that hold more information. RAM is now cheap and it is extremely affordable to purchase 16 or 32 GB memory cards. This is no longer an excuse!
  • Save your working and finished image files as a TIF. Once converted from RAW and you have enhanced your images, save those final images in a lossless file format and store that securely. Only use JPG for sharing, but every time you need to work on that file to make revisions, go back to the lossless file.
  • Stop saving over JPG files! As mentioned above, every time that you open and re-save a lossy compression file like JPGs, you lose image quality and before you know it, you will be left with an image of mush.