Makes a series of A3 posters for cutting from a bunch of images

make-posters.rb

#!/usr/bin/env ruby

# This script makes a series of A3 posters for cutting from a bunch of images.

require "rational"

R_4_3 = Rational(4, 3)
R_3_4 = Rational(3, 4)

system "rm -rf out"
system "mkdir out"

images = {}

Dir.glob("*.jpg") do |file|
    info = `identify '#{file}'`
    w, h = info[/(\d+x\d+)/, 1].split("x").map(&:to_i)
    ratio = Rational(w, h)

    new_w = 0
    new_h = 0
    rotate = false

    if ratio == R_4_3
        new_w = w
        new_h = h
    elsif ratio == R_3_4
        new_w = h
        new_h = w
        rotate = true
    elsif w > h # horizontal
        if ratio > R_4_3
            new_h = h / 3 * 3
            new_w = new_h / 3 * 4
        else
            new_w = w / 4 * 4
            new_h = new_w / 4 * 3
        end
    else # vertical
        if ratio < R_3_4
            new_h = w / 3 * 3
            new_w = new_h / 3 * 4
        else
            new_w = h / 4 * 4
            new_h = new_w / 4 * 3
        end
        rotate = true
    end

    images[file] = {w: w, h: h, new_w: new_w, new_h: new_h, rotate: rotate}
end

min_w = images.map { |k, v| v[:new_w] }.min
min_h = images.map { |k, v| v[:new_h] }.min

images.each do |file, info|
    if info[:rotate]
        system "convert '#{file}' -resize #{min_h}x#{min_w}^ -gravity center -extent #{min_h}x#{min_w} -rotate 90 +repage 'out/#{file}'"
    else
        system "convert '#{file}' -resize #{min_w}x#{min_h}^ -gravity center -extent #{min_w}x#{min_h} +repage 'out/#{file}'"
    end
end

# Verify
Dir.glob("out/*.jpg") do |file|
    info = `identify '#{file}'`
    w, h = info[/(\d+x\d+)/, 1].split("x").map(&:to_i)
    ratio = Rational(w, h)

    if ratio != R_4_3
        puts "#{file} aspect raito is not 4:3 but #{ratio}"
    end
end

# Make tiles
system "montage out/*.jpg -tile 4x4 -geometry +1+1 -quality 100% out/poster_%d.jpg"