More Than JPEGs

Digital Photo Storage Formats and File Types

Digital photographers are all familiar with the JPG or JPEG filename extension for digital images, but the JPEG file type represents only one of many formats for digital photo storage. If you are concerned with image quality and if you use a photo editor, you may want to understand your options for photo storage.

A Little Computer Math

Digital photos are generally represented as a matrix of dots or pixels. Each pixel (picture element) is a color created by a combination of red, blue, and green colors each of which typically is represented by 8 bits (one byte) allowing 256 variations of red, blue, and green. Combined these provide 256 x 256 x 256 colors or approximately 16 million colors. So each pixel requires 24 bits (or three bytes). For a 1600 x 1200 pixel image, 1,920,000 pixels or 5,260,000 bytes (over 5 megabytes) of storage would be required. A 10 megapixel image would require about 30 megabytes of storage.

JPEG

I say “would” because, in reality, images are generally compressed to save space. This is generally done with some reduction in the quality of the image. One technique for doing this was defined by the “Joint Photographic Experts Group” (JPEG) and is the most common method for the storage of digital photo images today. Almost all digital cameras today store images in JPEG format. (I would say ALL, but there may be an exception out there somewhere that I don’t know about!) However, many cameras offer alternative storage options and photo editors always allow storage of images in other formats. (I really believe I am correct on the always this time.)

What Your Camera Captures

Your camera most certainly records images in JPEG format, but many cameras offer other formats such as RAW or TIFF for photo storage. When you select RAW format for your images, you are telling your camera to record all the information captured by the lens. There is no compression, no color correction, and no sharpening. The image data is not processed as it would be with JPEG format.  TIFF or Tagged Image File Format is processed, but, even though it may be compressed, there is no loss of picture quality.

RAW Format

When your images are stored in RAW, you have the highest quality image possible and that you can edit this file to correct exposure, color, sharpness and many other factors. However, there is not a standard RAW format. Each camera manufacturer has its own proprietary RAW format. Consequently, the file type is not “RAW”, but varies by camera: NEF for Nikon, CRW or CR2 for Canon, SR2 for Sony, ORF for Olympus, etc. This means that the photo editor you use to process RAW files must accommodate these unique manufacturer formats. Frequently a raw editor is distributed with your camera, available for download, or available in Adobe Photoshop and Photoshop Elements products. To eliminate this proprietary format issue, some editors, including Photoshop, allow the storage of files in DNG or Digital Negative format, that is a more standard format, although an Adobe one. RAW files are never compressed, so are very large, but provide the most information about the data captured by your camera.

TIFF Format

TIFF is a format designed to allow for compression of the image, but without any degradation of image quality. It is “lossless compression” as compared to JPEG compression that is “lossy” with varying degrees of quality depending on the amount of compression. Files store in TIFF format are not supported by most Internet Browsers, however. TIFF also provides less efficient compression than the newer PNG files.

PNG Format

PNG or Portable Network Graphics format is another lossless format that provides compression with no degradation to image quality. It was created as a replacement for GIF (Graphic Interchange Format), that, although an acceptable Internet format was limited to 256 colors. PNG is an excellent choice for storing photos as there is no loss of image quality, compression to reduce the file size, and compatibility with most Browsers. Many photo editors support saving images as PNG files. If you plan to produce large prints, this is an excellent format for storage.

More on JPEG

For most of us, JPEG will remain the file format of choice. While not providing the highest quality image storage, it significantly reduces file size. JPEG is compatible with all browsers with the smaller file sizes reducing the upload and download times required while providing quality more than sufficient for viewing on a computer screen. One word of caution, however, is that it is true that repeated loading and saving of a JPEG file will degrade the file quality, so this is not a good choice for photos that may be edited and re-edited. Finally, your camera as well as your photo editor allow for specification of the quality of a JPEG image. Higher quality means less compression and larger file sizes. I recommend specifying the highest quality in your camera and photo editor. The cost of higher capacity camera cards and computer storage is not the limitation it once was.

Still More…

This was intended to be a brief overview of file types. There is much more to be said about image files. This article addressed only raster (or bitmap) files. Vector files, generally used for high quality graphics, are an entirely different topic. I also did not discuss editor formats (such as Photoshop PSD files), image transparency, or image layers. Stay curious. Do research on your own. Experiment! Or send me your questions. I’d be happy to hear from you.

A Learning Opportunity

Pasco Parks and Recreation is offering a 3-session digital photography course on Saturday afternoons from 1:00 to 3:30 on June 14, 21, and 28.
Call them at 813-929-1220 for more information. We welcome e-mail with questions regarding classes or photo topics at: info@con2000.com.     
Online: www.con2000.com/photography.