# This routine needs the color_histogram method
# from either ImageMagick 6.0.0 or GraphicsMagick 1.1
# Specify an image filename as an argument.

require 'rmagick'

class PixelColumn < Array
  def initialize(size)
    super
    fill {Magick::Pixel.new}
  end

  def reset(bg)
    each {|pixel| pixel.reset(bg)}
  end
end

module Magick
  class Pixel
    def reset(bg)
      self.red = bg.red
      self.green = bg.green
      self.blue = bg.blue
      self.opacity = bg.opacity
    end
  end

  class Image
    private

      HISTOGRAM_COLS = 256
      HISTOGRAM_ROWS = 200
      MAX_QUANTUM = 255
      AIR_FACTOR = 1.025

      # The alpha frequencies are shown as white dots.
      def alpha_hist(freqs, scale, fg, bg)
        histogram = Image.new(HISTOGRAM_COLS, HISTOGRAM_ROWS) do
          self.background_color = bg
          self.border_color = fg
        end

        gc = Draw.new
        gc.affine(1, 0, 0, -scale, 0, HISTOGRAM_ROWS)
        gc.fill('white')

        HISTOGRAM_COLS.times do |x|
          gc.point(x, freqs[x])
        end

        gc.draw(histogram)
        histogram['Label'] = 'Alpha'

        histogram
      end

      def channel_histograms(red, green, blue, int, scale, fg, bg)
        rgb_histogram = Image.new(HISTOGRAM_COLS, HISTOGRAM_ROWS) do
          self.background_color = bg
          self.border_color = fg
        end
        rgb_histogram['Label'] = 'RGB'
        red_histogram   = rgb_histogram.copy
        red_histogram['Label'] = 'Red'
        green_histogram = rgb_histogram.copy
        green_histogram['Label'] = 'Green'
        blue_histogram  = rgb_histogram.copy
        blue_histogram['Label'] = 'Blue'
        int_histogram = rgb_histogram.copy
        int_histogram['Label'] = 'Intensity'
        int_histogram.matte = true

        rgb_column   = PixelColumn.new(HISTOGRAM_ROWS)
        red_column   = PixelColumn.new(HISTOGRAM_ROWS)
        green_column = PixelColumn.new(HISTOGRAM_ROWS)
        blue_column  = PixelColumn.new(HISTOGRAM_ROWS)
        int_column   = PixelColumn.new(HISTOGRAM_ROWS)

        HISTOGRAM_COLS.times do |x|
          HISTOGRAM_ROWS.times do |y|
            yf = Float(y)
            if yf >= HISTOGRAM_ROWS - (red[x] * scale)
              red_column[y].red = QuantumRange
              red_column[y].green = 0
              red_column[y].blue = 0
              rgb_column[y].red = QuantumRange
            end
            if yf >= HISTOGRAM_ROWS - (green[x] * scale)
              green_column[y].green = QuantumRange
              green_column[y].red = 0
              green_column[y].blue = 0
              rgb_column[y].green = QuantumRange
            end
            if yf >= HISTOGRAM_ROWS - (blue[x] * scale)
              blue_column[y].blue = QuantumRange
              blue_column[y].red = 0
              blue_column[y].green = 0
              rgb_column[y].blue = QuantumRange
            end
            if yf >= HISTOGRAM_ROWS - (int[x] * scale)
              int_column[y].opacity = TransparentOpacity
            end
          end

          rgb_histogram.store_pixels(  x, 0, 1, HISTOGRAM_ROWS, rgb_column)
          red_histogram.store_pixels(  x, 0, 1, HISTOGRAM_ROWS, red_column)
          green_histogram.store_pixels(x, 0, 1, HISTOGRAM_ROWS, green_column)
          blue_histogram.store_pixels( x, 0, 1, HISTOGRAM_ROWS, blue_column)
          int_histogram.store_pixels(  x, 0, 1, HISTOGRAM_ROWS, int_column)
          rgb_column.reset(bg)
          red_column.reset(bg)
          green_column.reset(bg)
          blue_column.reset(bg)
          int_column.reset(bg)
        end

        [red_histogram, green_histogram, blue_histogram, rgb_histogram, int_histogram]
      end

      # Make the color histogram. Quantize the image to 256 colors if necessary.
      def color_hist(fg, bg)
        img = number_colors > 256 ? quantize(256) : self

        begin
          hist = img.color_histogram
      rescue NotImplementedError
        $stderr.puts 'The color_histogram method is not supported by this version '\
                     'of ImageMagick/GraphicsMagick'

        else
          pixels = hist.keys.sort_by {|pixel| hist[pixel] }
          scale = HISTOGRAM_ROWS / (hist.values.max*AIR_FACTOR)

          histogram = Image.new(HISTOGRAM_COLS, HISTOGRAM_ROWS) do
                self.background_color = bg
                self.border_color = fg
              end

          x = 0
          pixels.each do |pixel|
            column = Array.new(HISTOGRAM_ROWS).fill {Pixel.new}
            HISTOGRAM_ROWS.times do |y|
              if y >= HISTOGRAM_ROWS - (hist[pixel] * scale)
                column[y] = pixel
              end
            end
            histogram.store_pixels(x, 0, 1, HISTOGRAM_ROWS, column)
            x = x.succ
          end

          histogram['Label'] = 'Color Frequency'
          return histogram
        end
      end

      # Use AnnotateImage to write the stats.
      def info_text(fg, bg)
        klass = class_type == DirectClass ? 'DirectClass' : 'PsuedoClass'

        text = <<-END_TEXT
Format: #{format}
Geometry: #{columns}x#{rows}
Class: #{klass}
Depth: #{depth} bits-per-pixel component
Colors: #{number_colors}
            END_TEXT

        info = Image.new(HISTOGRAM_COLS, HISTOGRAM_ROWS) do
              self.background_color = bg
              self.border_color = fg
            end

        gc = Draw.new

        gc.annotate(info, 0, 0, 0, 0, text) do
          self.stroke = 'transparent'
          self.fill = fg
          self.gravity = CenterGravity
        end
        info['Label'] = 'Info'

        info
      end

      def intensity_hist(int_histogram)
        gradient = (Image.read('gradient:#ffff80-#ff9000') { self.size="#{HISTOGRAM_COLS}x#{HISTOGRAM_ROWS}" }).first
        int_histogram = gradient.composite(int_histogram, CenterGravity, OverCompositeOp)

        int_histogram['Label'] = 'Intensity'

        int_histogram
      end

      # Returns a value between 0 and MAX_QUANTUM. Same as the PixelIntensity macro.
      def pixel_intensity(pixel)
        (306*(pixel.red & MAX_QUANTUM) + 601*(pixel.green & MAX_QUANTUM) + 117*(pixel.blue & MAX_QUANTUM))/1024
      end

    public

      # Create the histogram montage.
      def histogram(fg='white', bg='black')
        red   = Array.new(HISTOGRAM_COLS, 0)
        green = Array.new(HISTOGRAM_COLS, 0)
        blue  = Array.new(HISTOGRAM_COLS, 0)
        alpha = Array.new(HISTOGRAM_COLS, 0)
        int   = Array.new(HISTOGRAM_COLS, 0)

        rows.times do |row|
          pixels = get_pixels(0, row, columns, 1)
          pixels.each do |pixel|
            red[pixel.red & MAX_QUANTUM] += 1
            green[pixel.green & MAX_QUANTUM] += 1
            blue[pixel.blue & MAX_QUANTUM] += 1

            # Only count opacity channel if some pixels are not opaque.
            unless opaque?
              alpha[pixel.opacity & MAX_QUANTUM] += 1
            end
            v = pixel_intensity(pixel)
            int[v] += 1
          end
        end

        # Scale to chart size. When computing the scale, add some "air" between
        # the max frequency and the top of the histogram. This makes a prettier chart.
        # The RGBA and intensity histograms are all drawn to the same scale.

        max = [red.max, green.max, blue.max, alpha.max, int.max].max
        scale = HISTOGRAM_ROWS / (max*AIR_FACTOR)

        charts = ImageList.new

        # Add the thumbnail.
        thumb = copy
        thumb['Label'] = File.basename(filename)
        charts << thumb

        # Compute the channel and intensity histograms.
        channel_hists = channel_histograms(red, green, blue, int, scale, fg, bg)

        # Add the red, green, and blue histograms to the list
        charts << channel_hists.shift
        charts << channel_hists.shift
        charts << channel_hists.shift

        # Add Alpha channel or image stats
        if !opaque?
          charts << alpha_hist(alpha, scale, fg, bg)
        else
          charts << info_text(fg, bg)
        end

        # Add the RGB histogram
        charts << channel_hists.shift

        # Add the intensity histogram.
        charts << intensity_hist(channel_hists.shift)

        # Add the color frequency histogram.
        charts << color_hist(fg, bg)

        # Make a montage.
        histogram = charts.montage do
          self.background_color = bg
          self.stroke = 'transparent'
          self.fill = fg
          self.border_width = 1
          self.tile         = '4x2'
          self.geometry     = "#{HISTOGRAM_COLS}x#{HISTOGRAM_ROWS}+10+10"
        end

        histogram
      end
  end
end

puts <<END_INFO

This example shows how to get pixel-level access to an image.
Usage: histogram.rb <image-filename>

END_INFO

# Get filename from command line.
if !ARGV[0]
  puts 'No filename argument. Defaulting to Flower_Hat.jpg'
  filename = '../doc/ex/images/Flower_Hat.jpg'
else
  filename = ARGV[0]
end

# Only process first frame if multi-frame image
image = Magick::Image.read(filename)
if image.length > 1
  puts 'Charting 1st image'
end
image = image.first

# Give the user something to look at while we're working.
name = File.basename(filename).sub(/\..*?$/,'')
$defout.sync = true
printf "Creating #{name}_Histogram.miff"

timer = Thread.new do
  loop do
    sleep(1)
    printf '.'
  end
end

# Generate the histograms
histogram = image.histogram(Magick::Pixel.from_color('white'), Magick::Pixel.from_color('black'))

# Write output file
histogram.compression = Magick::ZipCompression
histogram.write("./#{name}_Histogram.miff")

Thread.kill(timer)
puts 'Done!'
exit