Screenshot

gistfile1.rb

require "GD"

class Screenshot

  attr_accessor :frame, :width, :height, :pid, :rate, :quality, :token, :framesPerSourceImage, :programme, :workingCopy
  
  #
  def initialize(opts)

    # rate at which frames have been extracts - Eg, 1 = 1 fp/s, 0.2 = 1 frame every 5s
    @rate = 1.0
    
    # frames per source image block
    @framesPerSourceImage = 28800 / 480

    # an instance of GD::Image that gets update with the latest 'copy' of the working image as it's modified/cropped/resized across the class
    # it's this one you want to serialise to png/jpg 
    @workingCopy

    # parameters
    @token = opts['token']
    @pid = opts['pid']        
            
    # fetch the programme data from redux
    @programme = Redux::programme @pid, @token

    @frame = opts['frame'].to_i || (@programme[:duration] / 2) # centre frame if none given
    @width = ((opts['width']) && opts['width'] > 0) ? opts['width'] : 480
    @height = ((opts['height']) && opts['height'] > 0) ? opts['height'] : 270
    @quality = opts['quality'] || nil
               
  end

  # Returns a File object containing a screengrab
  def frame

    @frameSourceFile = Redux::frames @frame
            
    # calculate which file the frame can be found in, Eg, the 321st frame is in the file called '00300.jpg'
    @sourceFile = "%05d" % ((@frame / 60).floor * 60)
    @offset = (@frame / @rate) % 60
  
    # open-uri returns a class of type Tempfile, GD requires a class of type File, so we use .path to locate the temporary file via File.new()
    @workingCopy = GD::Image.newFromJpeg File.new(@frameSourceFile.path)
    self.crop(480 * @offset, 0, 480, 270)
    @workingCopy = self.resize(@width, @height)
    @workingCopy
  end

  # Montage, nothing more than a proxy to the image, I.e. no processing required
  def montage
    @frameSourceFile = Redux::montage
    return nil if ( @frameSourceFile == nil)
    @workingCopy = GD::Image.newFromJpeg File.new(@frameSourceFile.path)
    @workingCopy
  end

  # Returns a cropped image
  def crop(startX, startY, cropWidth, cropHeight)
   im = GD::Image.newTrueColor(cropWidth, cropHeight)
   foo = @workingCopy.copyResampled(im, 0, 0, startX, startY, cropWidth, cropHeight, cropWidth, cropHeight)
   @workingCopy = im
   im
  end

  # Return a resized image
  def resize(w, h)
    im = GD::Image.newTrueColor(w, h)
    foo = @workingCopy.copyResampled(im, 0, 0, 0, 0, w, h, 480, 270)
    @workingCopy = im
    im
  end

  # Serialise as a JPEG
  def to_jpg(quality=@quality)
    @workingCopy.jpegStr quality
  end

  # Serialise as a PNG
  def to_png
    @workingCopy.pngStr 
  end

  # Return the average RGB value of the image working copy
  def rgb
    r = 0
    g = 0
    b = 0
    
    w = @workingCopy.width
    h = @workingCopy.height

    pixels = w * h

    # loop over each pixel from top to bottom, left to right
    (1..h).each do |y|
      (1..w).each do |x|
        pixel = @workingCopy.getPixel(x, y)
        r += @workingCopy.red(pixel)
        g += @workingCopy.green(pixel)
        b += @workingCopy.blue(pixel)
      end
    end

    # ....
    rgb = [(r/pixels),(g/pixels),(b/pixels)]
  end
  
end