Tuesday, 23 February 2021

Colour Names 2

The companion colournames.html web page, contains experiments with naming colours.

As mentioned previously, HTML5/CSS colour names are highly subjective and lists have developed organically over many decades. As the 140 unique names mentioned in the first post derive from the original X11 list, I'll refer to them as X11 colours.

When plotted in RGB space, it is obvious that named X11 colours aren't evenly distributed:

The 140 unique X11 colours plotted in RGB space

There is a large cluster of very pale (near white) colours. But what about hue distribution?

A simplistic mechanism for dividing a colour space is to slice it up according to HSL parameters. If we use the following pseudocode, we get nine colour groups:

if lightness >= 95% then group = "whites"
else if saturation <= 15% then group = "blacks"
else if hue < 20° or hue >= 320° then group = "reds"
else if hue < 45° then group = "oranges"
else if hue < 75° then group = "yellows"
else if hue < 155° then group = "greens"
else if hue < 185° then group = "aquas"
else if hue < 255° then group = "blues"
else group = "purples"

For the X11 colours, we get 12 whites, 9 blacks, 23 reds, 20 oranges, 12 yellows, 17 greens, 14 aquas, 19 blues and 14 purples. This sounds like a fairly good distribution until you plot them as the number of colour names per degree of HSL hue:

X11 colour names per degree of HSL hue

We can see that the red-orange-yellow hue range is much more crowded.

One way to deal with this lack of uniform distribution is to pick colour points that are uniformly distributed and then name those points according to some dictionary. Our first attempt could be to pick RGB colours at regular intervals.

Web-safe colours are limited to six levels for each RGB channel (0%, 20%, 40%, 60%, 80% and 100%) for a total of 216 distinct colours. However, they are mostly unnamed. If we reduce the number of levels to five (0%, 25%, 50%, 75% and 100%), we get 125 distinct colours, similar to the number of X11 colours. Obviously, the X11 colours won't align perfectly, so there must be some fettling.

In the process of performing this experiment, I found that jan Misali has attempted something very similar. But it's an experiment, right? So repeating it cannot hurt.

The names in the so-called RGB-125 dictionary come from a variety of sources:
I also wanted the colour names to be single words, without qualifiers and unambiguous. For instance, "Chocolate" has very different RGB values in the various source dictionaries. "Lavender" is another example.

To compare colours objectively, I used the CIELAB ΔE*(1994) colour difference metric purely because there was a JavaScript function readily available. I should probably have used CIEDE2000, not least because the CIE94 algorithm is frustratingly quasimetric , i.e. CIE94(a, b) ≠ CIE94(b, a).

I had to invent ten names: "majorelle", "leaf", "lagoon", "felicia", "frog", "lettuce", "roxo", "sororia", "limon" and "kovidar".

See the full RGB-125 table here.

Thursday, 18 February 2021

Tetrascii 3

I took the plunge and animated the tetromino character set with each glyph made up of 25 pieces falling in order: https://chilliant.com/tetrascii.html

The final code to produce the animations is surprisingly concise, but the process of generating the data tables was a bit more involved.

Firstly, I originally drew each glyph in PowerPoint, so the construction wasn't very data-friendly. I had to screen-grab the slide and process the resultant image via JavaScript and HTML5 canvas elements.

Each screen-grabbed glyph was "pixel walked" to work out which of the 10x10 texels were directly connected to their neighbours. From the 100 texel neighbour data, I was able to reconstruct the shape, position and orientation of the 25 tetrominoes that made up the glyph. The pixel intensity was used to determine if a tetromino was foreground or background.

The 25 tetrominoes for each glyph were ordered so that they stacked correctly, from bottom to top. This involved finding candidates (pieces whose lower boundaries all fit exactly on top of existing pieces) and picking a random candidate. Note that this simple scheme disallows overhangs, so pieces can drop vertically.

The glyphs are string-encoded as 25 groups of three characters: "<letter><x><y>".

"<letter>" indicates the shape and orientation of the piece. Lowercase letters are background pieces, uppercase are foreground:

     +---- +---- cyan
AB   |#### |#
     |     |#
     |     |#
     |     |#

     +---- +---- +---- +---- orange
EFGH |###  |##   |  #  |#
     |#    | #   |###  |#
     |     | #   |     |##
     |     |     |     |

     +---- +---- +---- +---- blue
IJKL |###  | #   |#    |##
     |  #  | #   |###  |#
     |     |##   |     |#
     |     |     |     |

     +---- +---- +---- +---- purple
MNOP |###  | #   | #   |#
     | #   |##   |###  |##
     |     | #   |     |#
     |     |     |     |

     +---- +---- red
QR   |##   | #
     | ##  |##
     |     |#
     |     |

     +---- +---- green
UV   | ##  |#
     |##   |##
     |     | #
     |     |

     +---- yellow
Y    |##

"<x><y>" is the coordinate within the 10x10 glyph grid of the top-left corner of the piece.

The resultant 75-character encoding for each glyph therefore encapsulates:

  • The order that the pieces fall
  • The shape and orientation of each piece
  • The column that each piece falls in
  • The row that each piece comes to rest on
  • The colour of each piece
A few more hoops have to be jumped through to convert this information into the final animated SVG elements, but that's because of the baroque relationships between SVG, HTML and CSS.

Wednesday, 10 February 2021

Tetrascii 2

Well, it turns out that the Tetrascii lowercase letters are relatively easy if you open up the smaller counters:


It's not too bad a bitmap font, given the limitations imposed. Some of the glyphs are necessarily quirky, but that just adds character. Cough, cough.

Tetrascii 1

What do we get when you cross two old computer phenomena: ASCII and Tetris?


The "rules" are as follows:
  1. Each glyph must fit within a 10x10 grid.
  2. The foreground pixels must be constructible from standard tetrominoes.
  3. The background pixels (including counters) must be constructible from standard tetrominoes.
It's surprisingly difficult to construct a readable font. Obviously, I've cheated with the lowercase letters; but in my defence, the counters of the uppercase letters are hard enough. The minimum counter size is four pixels and you can see the trouble I had with the dollar sign.

A project for another time would be to animate the construction of text by falling pieces.