Irregular Webcomic! #2571

Lossy compression is a method of compressing digital data files so that they take up less storage space, with the characteristic that the original data cannot be recovered exactly from the compressed file.

Why would this be useful? Well, firstly there is another type of compression called lossless compression, which compresses data files into smaller files in such a way that you can reverse the procedure and recover exactly what you started with. That sounds great, and in fact is what is needed for compressing files containing things like financial records, scientific data, or your latest novel. When you uncompress your compressed data file, you want the exact same information you put in.

So why don't we just use that all the time? Because there are some types of files for which it doesn't matter so much if you lose some of the original information. And if we don't care about losing a bit of the original data, then we can compress the file into a smaller size than if we used lossless compression.

What sort of files might you not care if you lose some of the data? There are lots of them: photos, music and other audio files, and videos. For these sorts of files, a little bit of loss of quality is often acceptable, especially if it means you can fit 1000 songs on your iPod rather than just 30, or if you can take 500 photos with your camera rather than just 50.

While some people claim they can detect the loss of quality in images or music when the file is compressed in a lossy fashion, if it's done right then the information which is lost will be stuff that is imperceptible to a human being when you either view an image or listen to an audio file. It can be done wrong too - in which case the quality will be obviously affected - but most lossy compression algorithms these days are pretty good and you'd be very hard pressed to notice the tiny difference between the original and the compressed version.

In fact, the compression algorithms are deliberately tuned so that the parts that are lost are precisely the parts that human beings are the worst at noticing in the first place. The bits that we pay most attention to are retained in their detail, and the bits that humans don't notice are thrown away or reduced in quality. It's really quite clever stuff.

Indeed, if only it could be applied to our work schedules, tasks, and deadlines...

2024-03-31 Rerun commentary: Unfortunately I only saved the first 223 Irregular Webcomic! strips as JPEG files, with lossy image compression. From 224 onwards I saved Photoshop files, which are compressed losslessly, so I can modify and create different versions without losing quality if I want to.

Well, except that comics that early are saved at the now relatively tiny resolution of 730×260 pixels. Now I make comics at 2030×680 pixels, almost 3 times the resolution in both dimensions.