I think the idea that a bar chart is usually improved by narrowing its bars while keeping them in the same positions is pretty silly. Yes, the article does say that one can take it too far, but I think that's the wrong framing. It's not that using less ink is good, but sometimes if you take that too far then it competes with visual clarity. Visual clarity is always the goal; sometimes clearer designs have more non-data ink, sometimes less; many designs are too busy so "less non-data ink" is usually good, but not always.
Tufte's "data-ink ratio" is a pretty good heuristic, but e.g. it would probably become a better match for actual visual clarity if what you counted wasn't "amount of ink" but something that measures spatial change in ink. It's the transitions that feel like noise, much more than patches of constant colour. But "data-ink ratio" is easier to say and easier to read than "ratio of integral of norm of gradient of colour".
Also, I think this sort of graph is better with very light gridlines than with no gridlines, though I think Tufte would disagree.
Also also, in Tufte's book, immediately before the section about "data-ink" there is an copy of a graph drawn by Playfair showing a country's balance of trade over time. Tufte gives it as an example of a good informational graphic. You can see it at https://en.wikipedia.org/wiki/William_Playfair#/media/File:P... if you like. This graph uses shading to indicate which direction the balance of trade goes in; that information is completely redundant with the curves by which the shading is bounded; but it would very much not be improved by removing that "redundant" ink even though according to his principles as interpreted by the page linked here that would make a huge improvement in the data-ink ratio.
If you only take that idea in one direction then I agree that it is pretty silly. However, the spirit of the visualization suggests finding a balance and optimizing the data-ink ratio rather than searching for a perfect value. If you follow the link you'll find the article I wrote talking about this: https://scienceux.org/articles/data-ink-ideal-vs-minimal
All the points that you make are very much valid, and it is good that you have pointed these things out because I wouldn't want people to follow these principles blindly without thinking about it for themselves.
I haven't considered the 'ratio of integral of norm of gradient of colour' too much (because it is easier to start simple and build on it), but I hope you might consider elaborating on it.
Narrowing the bars is not reducing non-data ink ratio imo and against the spirit. The bars are the data. And they therefore should be maximally visible, the same way that you BOLD text (make it thicker) that you want to emphasize rather than thin it to "reduce non-message ink ratio."
For the width of the bar there is practically speaking a middle ground that uses thick bars but not too thick/close together such that it harms legibility.
Exactly, in this case the middle ground is right, just as with text, if everything is highlighted as BOLD UPPER CASE, then effectively nothing in the message is highlighted
Tufte's "data-ink ratio" is a pretty good heuristic, but e.g. it would probably become a better match for actual visual clarity if what you counted wasn't "amount of ink" but something that measures spatial change in ink. It's the transitions that feel like noise, much more than patches of constant colour. But "data-ink ratio" is easier to say and easier to read than "ratio of integral of norm of gradient of colour".
Also, I think this sort of graph is better with very light gridlines than with no gridlines, though I think Tufte would disagree.
Also also, in Tufte's book, immediately before the section about "data-ink" there is an copy of a graph drawn by Playfair showing a country's balance of trade over time. Tufte gives it as an example of a good informational graphic. You can see it at https://en.wikipedia.org/wiki/William_Playfair#/media/File:P... if you like. This graph uses shading to indicate which direction the balance of trade goes in; that information is completely redundant with the curves by which the shading is bounded; but it would very much not be improved by removing that "redundant" ink even though according to his principles as interpreted by the page linked here that would make a huge improvement in the data-ink ratio.