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Print a 256-colour test pattern in the terminal
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#!/bin/bash | |
# Tom Hale, 2016. MIT Licence. | |
# Print out 256 colours, with each number printed in its corresponding colour | |
# See http://askubuntu.com/questions/821157/print-a-256-color-test-pattern-in-the-terminal/821163#821163 | |
set -eu # Fail on errors or undeclared variables | |
printable_colours=256 | |
# Return a colour that contrasts with the given colour | |
# Bash only does integer division, so keep it integral | |
function contrast_colour { | |
local r g b luminance | |
colour="$1" | |
if (( colour < 16 )); then # Initial 16 ANSI colours | |
(( colour == 0 )) && printf "15" || printf "0" | |
return | |
fi | |
# Greyscale # rgb_R = rgb_G = rgb_B = (number - 232) * 10 + 8 | |
if (( colour > 231 )); then # Greyscale ramp | |
(( colour < 244 )) && printf "15" || printf "0" | |
return | |
fi | |
# All other colours: | |
# 6x6x6 colour cube = 16 + 36*R + 6*G + B # Where RGB are [0..5] | |
# See http://stackoverflow.com/a/27165165/5353461 | |
# r=$(( (colour-16) / 36 )) | |
g=$(( ((colour-16) % 36) / 6 )) | |
# b=$(( (colour-16) % 6 )) | |
# If luminance is bright, print number in black, white otherwise. | |
# Green contributes 587/1000 to human perceived luminance - ITU R-REC-BT.601 | |
(( g > 2)) && printf "0" || printf "15" | |
return | |
# Uncomment the below for more precise luminance calculations | |
# # Calculate percieved brightness | |
# # See https://www.w3.org/TR/AERT#color-contrast | |
# # and http://www.itu.int/rec/R-REC-BT.601 | |
# # Luminance is in range 0..5000 as each value is 0..5 | |
# luminance=$(( (r * 299) + (g * 587) + (b * 114) )) | |
# (( $luminance > 2500 )) && printf "0" || printf "15" | |
} | |
# Print a coloured block with the number of that colour | |
function print_colour { | |
local colour="$1" contrast | |
contrast=$(contrast_colour "$1") | |
printf "\e[48;5;%sm" "$colour" # Start block of colour | |
printf "\e[38;5;%sm%3d" "$contrast" "$colour" # In contrast, print number | |
printf "\e[0m " # Reset colour | |
} | |
# Starting at $1, print a run of $2 colours | |
function print_run { | |
local i | |
for (( i = "$1"; i < "$1" + "$2" && i < printable_colours; i++ )) do | |
print_colour "$i" | |
done | |
printf " " | |
} | |
# Print blocks of colours | |
function print_blocks { | |
local start="$1" i | |
local end="$2" # inclusive | |
local block_cols="$3" | |
local block_rows="$4" | |
local blocks_per_line="$5" | |
local block_length=$((block_cols * block_rows)) | |
# Print sets of blocks | |
for (( i = start; i <= end; i += (blocks_per_line-1) * block_length )) do | |
printf "\n" # Space before each set of blocks | |
# For each block row | |
for (( row = 0; row < block_rows; row++ )) do | |
# Print block columns for all blocks on the line | |
for (( block = 0; block < blocks_per_line; block++ )) do | |
print_run $(( i + (block * block_length) )) "$block_cols" | |
done | |
(( i += block_cols )) # Prepare to print the next row | |
printf "\n" | |
done | |
done | |
} | |
print_run 0 16 # The first 16 colours are spread over the whole spectrum | |
printf "\n" | |
print_blocks 16 231 6 6 3 # 6x6x6 colour cube between 16 and 231 inclusive | |
print_blocks 232 255 12 2 1 # Not 50, but 24 Shades of Grey |
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