Ask the Teaboy

Q: Some people say I should be careful when using JPEG's because I can lose quality. What are they on about?

A: Excellent question. The JPEG image file is a compressed file type. In other words - at time of saving the file is made smaller (compressed), and consequently a small amount of data is lost. Some data is lost because the JPEG file uses what is called 'lossy compression' instead of 'lossless compression'. The amount of image data lost depends on how much compression is applied at the time of saving. Image editing software (or your cameras menu) gives you the option to choose how much compression to apply at the time of saving your JPEG file. The higher the compression, the smaller the file, and the greater the subsequent loss in quality.

Q: But why do digital cameras use JPEG files then?

A: Be aware that a print produced from the same scene photographed twice - once as a RAW or Tiff, and once as JPEG - will usually be impossible to tell apart. A JPEG saved with only a small amount of compression will be much smaller than a TIFF or RAW file, but offers extremely high quality reproduction. It's also fairly safe to say that if the Joint Photographics Experts Group (hence the name 'JPEG') didn't invent the JPEG image file type, digital cameras wouldn't be what they are today!! For more information on the relative pro's and con's of shooting with JPEG or RAW, please read this article on RAW files.

Q: How, then, can I use JPEG's and yet avoid loss of quality of my images?

A: The big thing to understand with JPEG's is that compression occurs at the time of saving. It is thus a bad idea to open your JPEG, edit it, and then save again as a JPEG. If you intend to edit your image, open the JPEG file and immediately save it in a format that doesn't compress - like a Tiff or PSD (Photoshop) file for example. You can then edit and re-edit the file without worrying about the integrity of your image being compromised. In other words, always keep your original JPEG file in the state your camera originally recorded it, and save as TIFF files those that you desire to keep in an edited state (we recommend you archive your original JPEG files to CD).

JPEG Trivia: Did you know that two JPEG files taken with your digital camera using the same camera settings will still be different in size (as closed files) depending on the subject matter being photographed? If you photograph a white cat in front of a bleached wall the file will be smaller than if you photograph a parade. The more colours and detail, the larger the file will be. Having said that - as open files they'll be identical in size, as the open size is dependant on the pixel count (resolution) rather than the subject detail and colours.