Image Format

Close up of the GIF file format

Lossy file saved as both 20% and 80%

In effect, how the JPG standard worked was to rapidly reduce file sizes by averaging the color values of a pixel with those around it. This caused massive reductions in file sizes allowing photographers to post 500kb images in extremely small (20-100kb) files while controlling the loss of quality. To the right you’ll see an image saved at 20% quality to the left and 80% to the right, both the difference in quality and the method JPG uses to reach the results should be evident.

Before I go on, I want to pause and take note of a statement I made in the above description because I’m sure most people missed it or brushed past without much thought … the JPG file format was introduced to the world in 1992. This phrase is critical because it reinforces how much the world has changed in just 17 years. For those of you who are under 20 years old, you’ll most likely have never known a world without Facebook or YouTube but for the rest of us, we sometimes forget the Internet is for all purposes a fairly recent addition to the world. I’m 35 years old and I remember the first JPG photo that I saw, the introduction of this format changed the way we shared images over computers.  Notice that I said it changed the way we shared images over computers? There was no Internet, or at least not what you see today.

In 1996, Unisys became uppity and started threatening to sue over the LZW compression found in the GIF format so the world invented the Portable Network Graphic format (PNG), along the way the format improved upon most of the qualities of the GIF and lost the capacity for animation. The PNG format has 8 bit graphics similar to the GIF but also has 24 bit like the JPG and introduced a new level with 32 bit graphics. While it lacks support for animation, it includes transparant pixels like a GIF. Unlike a GIF, where those pixels can be on or off the PNG allows for alpha transparency making the format extremely flexible and also capable of compressing images. The problem with the PNG format, is that it produces large files.

So which is best? Actually that depends entirely on what you want to accomplish with the graphics. As you’ll see from the image above the file size of the graphic can range from ~25k to ~430k depending on the quality you’d like to achieve.  Photographers for example should use the JPG compression most often to ensure their images are strong, crisp and colorful while illustrators and others who work with line art will benefit from the GIF format. In the end, practicing and experimenting are the best ways to determine what you should be using.

A quick thank you to the Old Shoe Woman for posting the a wonderful photo Sunlight Under a Live Oak Tree on Flickr for me to use as part of this tutorial.