Irregular Webcomic! #2174

2021-05-29 Rerun commentary: And so we move all the way to black.

Or is it?

The way most displays work, even solid areas of black still emit some light, from the backlighting. You can notice this if you have a black object and put it next to the black area on the screen - you should see that the object is significantly darker than the "black" area on the screen. This will be easier to notice on older displays, as modern displays are being engineered to make the black areas as dark as they can make them, because a higher contrast ratio between the dark and light areas of the screen provides for a more vivid and natural looking image.

In fact, our perception of blackness is often—in fact usually—relative to surroundings. You can take almost any two objects that you'd describe as black and put them next to each other, and one will be noticeably darker than the other. Does that make the lighter one actually "grey", or is it still "black"? Either answer could be sensible depending on context.

And if you place your darkest black object next to something coated with good old Vantablack, your dark black object will look positively bright in comparison.

I remember vividly a lecture I attended on human vision and colour perception many years ago, when I was just learning about this stuff myself. The lecturer was using a projector in a very dark room, and he showed a slide that was dark/black except for a white square on one side. He asked us what colour the square was. Everyone said white. He showed us the next slide, in which the same square was there, but a brighter square appeared next to it. He asked us what colour the new square was, and everyone said white. Then he asked us what colour we thought the old square was, and we realised it was actually light grey.

He showed us the next slide, in which the same two squares were there, but another even brighter square appeared next to them. He asked us what colour the new square was, and everyone said white. Then he asked us what colour we thought the old squares were, and we realised they actually light grey and a somewhat darker grey.

He showed us the next slide, in which the same three squares were there, but another even brighter square appeared next to them. He asked us what colour the new square was, and everyone said white. Then he asked us what colour we thought the old squares were, and we realised they actually light grey and a somewhat darker grey, and an even darker grey.

You can see where this is going. In all there was a sequence of seven brighter squares. By the end of it, the original square that we'd all been convinced was white to start with now looked quite a dark grey in comparison to the brightest, whitest square. It was a very powerful presentation on the relativity of our brightness perception.