fix!: remove broken dominant border

[knarewski]

Background

I was looking into spec discrepancies between local development and github CI

When running specs on ubuntu 24.04, the "dominant" border rendered using completely different and clearly wrong colour. It turns out that the entire feature is thoroughly broken.

Expected (left) and actual (right) render of dominant coloured border on ubuntu 24.04

Problems

1. The generated histogram information is plain wrong, suggesting the colours which clearly aren't dominant. These are mostly blueish, with some brownish and two flashy greens. I don't know why that happens, possibly the image preprocessing somehow conflicts with the histogram option.

Test image and colours generated using current command on 24.04 ("dominant" colour at the bottom)

2. In the ubuntu 22.04's imagemagick version (used to find dominant colours), the pixel count is not padded, leading to incorrect sorting. That happened to have picked the brown-ish value for border colour in the spec example, which didn't look perfect but also wasn't so clearly wrong. However, ubuntu 24.04's imagemagick adds padding to pixel count, so the sorting is correct, but as per point 1. the entire histogram is wrong. This leads to selecting bright green colour for the border.

Test image and colours generated using current command on 22.04 (that one uses wrong sorting, "dominant" colour at the bottom)

Solution

The colorscore gem seems unmaintained, so one alternative is to reimplement dominant handling ourselves. What made the output sane to me was substituting current colorscore's command:

convert spec/fixtures/reference_images/plasma-no-op-output.jpg -resize 400x400 -format %c -dither None -quantize YIQ -colors 16 -depth 8 histogram:info:-

with the following one:

convert spec/fixtures/reference_images/plasma-no-op-output.jpg -resize 400x400 -format %c -dither None -quantize YIQ -colors 16 -depth 8 gif:- \
      | convert - -define histogram:unique-colors=true -format %c histogram:info:- \
      | sort

Test image and colours generated using fixed command on 24.04 (fixed sorting and behaviour, "dominant" colour at the bottom)

Ideally natural sorting should be used to handle unpadded output.

That said, I don't expect anyone to miss that feature, so I'm just removing it, leaving the hints about possible fix here in case that's needed :) .

References

original code from colorscore

Appendix

Raw convert output for original command on ubuntu 24.04

# convert spec/fixtures/reference_images/plasma-no-op-output.jpg -resize 400x400 -format %c -dither None -quantize YIQ -colors 16 -depth 8 histogram:info:- | sort
           979: (135,127,127) #877F7F yiq(135,127,127)
          1298: (104,128,127) #68807F yiq(104,128,127)
          3311: (151,127,127) #977F7F yiq(151,127,127)
          6098: (147,127,127) #937F7F yiq(147,127,127)
          6423: (48,87,197) #3057C5 yiq(48,87,197)
          7039: (70,190,195) #46BEC3 yiq(70,190,195)
          7360: (148,127,127) #947F7F yiq(148,127,127)
          7622: (50,66,193) #3242C1 yiq(50,66,193)
          8989: (51,93,176) #335DB0 yiq(51,93,176)
         11721: (57,157,178) #399DB2 yiq(57,157,178)
         12308: (76,162,165) #4CA2A5 yiq(76,162,165)
         12321: (102,127,127) #667F7F yiq(102,127,127)
         12525: (76,107,165) #4C6BA5 yiq(76,107,165)
         13314: (87,217,159) #57D99F yiq(87,217,159)
         18692: (80,248,173) #50F8AD yiq(80,248,173)

Raw convert output for original command on ubuntu 22.04 (note wrong order)

# convert spec/fixtures/reference_images/plasma-no-op-output.jpg -resize 400x400 -format %c -dither None -quantize YIQ -colors 16 -depth 8 histogram:info:- | sort
    11721: (57,157,178) #399DB2 yiq(57,157,178)
    12308: (76,162,165) #4CA2A5 yiq(76,162,165)
    12321: (102,127,127) #667F7F yiq(102,127,127)
    12525: (76,107,165) #4C6BA5 yiq(76,107,165)
    1298: (104,128,127) #68807F yiq(104,128,127)
    13314: (87,217,159) #57D99F yiq(87,217,159)
    18692: (80,248,173) #50F8AD yiq(80,248,173)
    3311: (151,127,127) #977F7F yiq(151,127,127)
    6098: (147,127,127) #937F7F yiq(147,127,127)
    6423: (48,87,197) #3057C5 yiq(48,87,197)
    7039: (70,190,195) #46BEC3 yiq(70,190,195)
    7360: (148,127,127) #947F7F yiq(148,127,127)
    7622: (50,66,193) #3242C1 yiq(50,66,193)
    8989: (51,93,176) #335DB0 yiq(51,93,176)
    979: (135,127,127) #877F7F yiq(135,127,127)