Compressing Picture Files for emailing

Don Bradbury looks at your options

Few things are more annoying than to log on for your email and find that someone not quite in the know has squirted to you several megabytes of picture files from their latest holiday or whatever, and for which you have to sit and twiddle your thumbs while it all downloads to your computer.

While those with fast Broadband access may not lose much sleep over this, dial-up users will be especially upset as the process can take tens of minutes to complete. In fact this lack of know-how can lose friends quicker than you can say "ADSL".

The know-how involves file compression, and that's carried out within a graphics editor such as Paint Shop Pro, for example. While your digital camera or scanner will probably let you save the images in JPEG format, and apply some compression on the fly in doing so, there's more to be had for the inveterate picture emailer.

An example

Say you have four pics to send to another computer user, each taken at 2048 x 1536 pixels resolution. They might amount to something over 2MB of data; far too much for regular emailing. In fact I tried four picture files at random from a digicam and they totalled 2073K. Now, what are the options?

First, decide what loss of quality you, or rather the receiver of your pictures, can tolerate, for the JPEG compression you are going to use is a so-called lossy process, inducing compression artefacts into your pictures that will be visible if the images are magnified too much. For all practical purposes, however, a great deal of compression can be applied before the pictures are essentially destroyed if the receiver merely wants to view them on screen.

To the four pictures I first applied 70% JPEG quality within Paint Shop Pro, using Save As for each image and entering a different filename - otherwise the compressed images would over-write the original higher quality ones, and you probably don't want that to happen. I then noted the amount of compression. It averaged 67.2%, no less, and the resultant images totalled just 679K; a very useful reduction but still probably too big for emailing.

Another image was then created from each original by resizing them to 40% of the starting size (number of Pixels) followed by the same 70% JPEG quality I used before in the Save As process. That achieved 92.6% reduction overall, with a final total file size of only 154K from the four pictures. That, I considered, would be tolerable for emailing. Even though compression artefacts were noticeable, such loss of quality was acceptable for the purpose.

If you ask the reasonable question, "why can't I just Zip the files (using Winzip or similar) and compress them that way"', the answer is that zipping JPG files achieves very little by way of compression. Take a look at the table of test results. The only advantage of zipping (which you might decide to apply to your already compressed files) would be that of sending a single file instead of several. But then your receiver would need to unzip the bundle, and you'd have to be sure he was equipped to do so.

Whatever the resolution from your originating source, copy a few files to a test folder and play around in your graphics editor to see what can be achieved before you think of sending multi-megabyte packages to your associates.

Summary

Don Bradbury