A Primer: The JPEG Bakery
As I’ve mentioned here before, digital photography has made life so much better. The ability to select an accurate white balance, choose the most favorable ISO speed, view images on the fly, just to name a few. To put these tasty morsels in play, we’ve had to expand our horizons and elevate our learning curves. Are you ready for more? Hang onto your hats, because here we go again. JPEG or RAW?
In case you already didn’t know it, JPEG is the acronym for the Joint Photographic Experts Group, the name of the committee that created the standards in 1986 for still image compression. According to Wikipedia, “JPEG itself specifies both the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, and the file format used to contain that stream.” Your camera makes adjustments to maximize the data, eliminating colors the eye can’t see and then compresses the image with a reduced color depth to save the file in the JPEG file format. Because this process discards what it decides is redundant data, JPEG is referred to as a lossy (not lousy) format. Keep in mind, however, that when the file is opened in a computer the lost data is for the most part well rebuilt, especially if a low compression ratio was used.
Unlike JPEG, RAW is a format that requires little or no internal processing by the camera. These files also contain lots more color information, which provides more data but that data now requires external processing. When choosing the RAW setting all of the raw data from the camera’s imager is saved without any kind of processing. Effects such as Contrast, Saturation and Sharpness are not applied to the image file. Perhaps these food analogies that my friend Barry Staver uses will help explain the difference between a RAW capture and a compressed (JPEG) capture:
- Cake. You can purchase one ready to eat in the bakery department of most grocery stores or you can make one at home from scratch. The store bought cake is like the JPEG, since most choices are made for you. The bakery decides what ingredients to add in what quantity to meet their standards. You take it as is. JPEG photographs are processed in-camera, compressed. You take it as is. On the other hand the scratch-made cake allows you to choose the ingredients, altering here and there to suit your personal taste. The same thing goes for the RAW images. You decide in post-production.
- Chocolate chip cookies. Off the shelf brand x, y, or z. The chips are already baked into each one, the softness of the cookie predetermined, all are uniform in size. The JPEG version. Baked at home with almost any recipe gives you these choices: milk, dark, or white chocolate chips, the number of chips to fold into the batter, and the size of the cookies baked. The RAW version.
When should you use RAW and when should you use JPEG? Ahh, there are lots of discussions on this subject and I direct you to what Scott Bourne and I have written over at the Photofocus blog. Read what we have to say and make up your own mind.
Barry Staver & Joe wrote “Better Available Light Digital Photography” that’s available from Amazon.com and better bookstores everywhere.