What makes files large?

How to talk to art students about file sizes anno domini 2025? The cloud computing paradigm has made it so that it is essentially no longer fundamental to know these kinds of things to get work done. You can drag and drop a 50 mega pixel photo in to Outlook and e-mail it without issue. Yet, there are practical, ecological and ultimately also creative advantages to knowing about and working with (size) limits.

Avery Lawrence invited Low-Tech Magazine to co-develop a workshop for students of animation at Stamps School of Art & Design at the University of Michigan. The goal was to both inform and then creatively explore compression in the context of animation. The workshop covered compression in a design sense (abstraction, simpler forms), in a technical sense (file sizes, file formats) and in a narrative sense (what is the minimum needed to tell a story).

To give students a sense of what makes files larger or smaller and what the parameters are for them to play with I made a short presentation that discusses four levers. N.b. everything below applies to a hypothetical file format that does not use additional compression.

When talking about an uncompressed file format there are essentially four levers or parameters you can play with. Each adds to total filesize.

Resolution is an obvious one. But what is unobvious is the squared relationship between file size and dimensions. In an uncompressed format, half the resolution equals a quarter of the size. The effect is in reverse when you have a larger resolution. This squared relationship means image size gives you your largest gains.

Colour depth is another. A ‘one bit’ color scheme gives you two colours (monotone). This is best thought of as when doing print work. You have the colour of the ink and the “nothing” which becomes the colour of the paper. A two-bit colour scheme gives you two additional colours. In the case of the tablet I drew this with, the only available ones are grey and white. Then there is full colour, a 24 bit color scheme. This gives you a whopping 16,777,216 colours. But ask yourself, how many of those are you actually using?

Frame Rate is an issue when considering moving images. With moving images, file size starts to have a time dimension as well. Less frames per second (fps) means a choppier animation but also less data per unit of time. More fps creates smoother animations at the expense of more data.

Given Frame Rate, the next parameter is how long the moving image lasts. Longer equals heavier filesize because more seconds equals more total frames.

So then you can think about file size as the product of these four different parameters. You can consider them levers or sliders that you can increase and decrease. To get a smaller file you can decrease them all a little. You can also opt to decrease three of them a lot and thereby fit a full length feature films on a 1.44mb floppy.

Of course the actual file format that you save things in determines a lot. Changing color depth only makes sense if you use a file format which actually uses indexed-colours (png, gif). So these four levers apply only to uncompressed files. Most file formats encode the data in clever ways whereby minimizing amount of colours or frames per second have less or even negative impact.