Isn't histogram an entirely different thing? As far as I know, to make a histogram you'd iterate over all pixels and, for each of them, increment histogram[pixelBrightness]. Here the author is not counting pixels, but exchanging coordinates.

Doesn't a histogram throw away the positional element of the pixel entirely and bin by the number of pixels at a particular brightness? This doesn't seem to do that ...

Yes it does. This is similar to what is shown on the video scopes of television engineers in the luma waveform view.

https://support.apple.com/kb/PH12688?locale=en_US&viewlocale...

You can keep one of the dimensions by making a histogram a 3d surface. 3d surface f(x,y)->z can be displayed as flat image with brightness representing z value. Brightness can be displayed using dithering. Putting all that together would result in more or less the same diagrams as described in article. With biggest difference being that information about left part of image is actually visible.

Swapping x with brightness is a bit misleading as dithering effect of white dots on black background give much stronger feeling of varied brightness than actual brightness.

Interesting. Do you have a link to such a histogram?

This type is actually known as a luma waveform histogram:

https://i.imgur.com/Gn4KQTW.png

Source: https://github.com/epistemex/scopes