I've only now got to test your regenerated version.  TTF is different but still utterly unreadable, but OTF became recognizable.  Not perfect (it's still lightgrey on dark grey), but far better.

Your commit moving embossed to FreeSerif came as I was about to respond.  It does solve my use case, thanks!

I attached samples on my setup (mostly run of the mill current Debian unstable) at 10pt.  It's a bit apples-to-oranges comparison though as the effective width differs despite nominal size being the same.

You know what...

I misread the specs in that very document.  It talks about the distancd from corresonding dots in neighboring cells, and I understood adjacent dots.

All this time, the patterns in FreeMono have been much too small, even according to the standard I thought I had followed.

This is not to say a different style is out of the question.  But first let's get the most important details right.

Adam, are you able to build the font yourself, or shall I get a copy to you?

I wonder, what if you moved current Braille to a face other than Mono, and either put non-embossed dots into Mono or leave that range empty?

My rationale being, the Mono face is used almost exclusively for terminals or to represent terminal text, where readability is paramount.  It's other faces that are used for fancy display.

I've played with different display settings a bit, and found that non-default antialiasing values make the problem even worse.  With antialiasing off, dots start getting recognizable only at massive 24pt.

Freefont can't use fancy "smart font" techniques that alter glyphs based on some variables like size, right?

(In case someone else reads this bug report: that initial request was #22995)

I'm afraid the Braille range (U+2800..U+28FF, FreeMono only) is useless in its current form.  At font sizes typically used for text I get nothing but greyish rectangles.  At 96 DPI, only around size 16 characters start getting recognizable, requiring a size of 22ish+ to be recognizable without difficulty.

Other fonts don't show non-embossed dots, and thus are perfectly readable even at very small sizes.

This is especially bad as FreeMono tends to get a high priority when searching for font substitutions, and thus prevents fonts with usable glyphs in this range from being used.

I'd suggest one of two solutions:

• remove Braille from FreeMono completely, letting other fonts such as DejavuSans, NotoSansSymbols, Symbola, etc fill in
• copy the range from a freely-licensed font.  This is generally not acceptable for Freefont, but as these characters don't involve any creativity, there's no "style" to be talking of.

An image sample attached, if you want some text that includes real Braille writing you can use for example https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt