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Tuesday, August 13, 2019

The Ultimate Digital Preservation Guide, Part Nine: More about file formats

For most of the history of photography and document reproduction, it has been a basic tenet that no copy can be any better than the original and copies of copies always degraded in quality. When digital images came along, all that changed. Theoretically, some digital images can be copied an infinite number of times without any degradation. However, this can only happen when the digital image is entirely reproduced. Many of today's digital image file formats are "lossy." That means that when the file is saved the saved copy has discarded some of the information (detail) of the original image. The most common of these lossy file formats is the ubiquitous JPEG file (.jpg, .jpeg, etc.).

At this point, it is important to realize that there are hundreds of different digital image file formats out there. If you find an image cannot be opened in some strange file format, I suggest doing a Google search on the applications that support that particular file extension. I will only be able to discuss some of the more commonly used file formats. You can usually tell the type of file format from the file extension (the letters after the file name following a dot or period). You can find a fairly complete list of file extensions in Wikipedia: List of filename extensions.

The reason that JPEG or JPG files lose information or detail is that the original file is compressed and the compression process discards some information. Now, if you use a camera or scanner and save the file in JPEG or JPG format, you will get most of the information from the device. It mostly when the original digital image is copied or edited that the image loses additional information. Some cameras and a few scanners will allow you to save images as RAW images. This file format preserves all of the original information from the device. When you edit a RAW image, you can save your changes in many other formats and the original RAW image is not altered. The RAW image is not so much a file format as it is a complete dump of all the information gathered by the camera or scanner's sensor.

An alternative to saving images as .jpeg or .jpg files is to use the .tiff or .tff format. TIFF (Tagged Image File Format) is a file compression format that does not lose any information; it is a lossless file format. Files saved from the digital devices in this particular format are much larger in size than JPEG and RAW files, but few cameras have the ability to create images in the TIFF format. There are a very large number of other file formats out there in common use. Here are a few more:

  • HEIC - currently used by newer Apple iPhone operating systems. Here is a link to an article entitled, "HEIC JPG Comparison: What’s the Difference between HEIC vs JPG?"
  • PNG - "A PNG file is an image file stored in the Portable Network Graphic (PNG) format. It contains a bitmap of indexed colors and uses lossless compression, similar to a .GIF file but without copyright limitations. PNG files are commonly used to store graphics for web images." See
  • .GIF Again quoting A GIF file is an image file often used for web graphics. It may contain up to 256 indexed colors with a color palette that may be a predefined set of colors or may be adapted to the colors in the image. GIF files are saved in a lossless format, meaning the clarity of the image is not compromised with GIF compression.

The scanning software that comes with your scanner may or may not have the ability to save files in all the different file formats

In the past, the file size was a huge issue. Most of the commonly used file formats such as JPEG and TIFF were either used or not used when memory storage was limited. Presently, file size is not as much of an issue. If your computer is old and you do not have external storage, you may still have some concerns about file size but even if that is the case, you can purchase sufficient external storage for a very reasonable price. See The Ultimate Digital Preservation Guide, Part Eight -- Technological Challenges: Scanners. If you have the option, store your images as RAW images. If not, then use TIFF. In event you have neither, JPEG will do. One more option is storing the images in PDF format. This is acceptable to the Library of Congress and is another alternative. Technically, PDF files are not an image format, but images can be stored as PDF files.

Here are the previous posts in this series:

Part One:
Part Two:
Part Three:
Part Four:
Part Five:
Part Six:
Part Seven:
Part Eight:

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