From: ara.t.howard@...
Date: 2006-04-07T02:46:03+09:00
Subject: Re: Creating images from pixel data (RMagick?)

On Thu, 6 Apr 2006, Tim Blair wrote:

> require 'RMagick'
> class RippedImage
>  def initialize (job_id, width, height)
>    @job_id = job_id.to_s;
>    @width = width.to_i;
>    @height = height.to_i;
>    @canvas = Magick::Image.new(@width, @height)
>    @pixels = []
>  end
>  def draw (c)
>    # the colour is a 6 digit hex char which needs to
>    # be converted to numeric values for RGB
>    col = []
>    c.scan(/../).each { |bit| col << bit.hex }
>    @pixels << Magick::Pixel.new(col[0], col[1], col[2], 0)
>  end
>  def finalize (type="gif")
>    @canvas.store_pixels(0, 0, @width, @height, @pixels)
>    @canvas.write("#{@job_id}.#{type}")
>  end
> end
>
> x = 512
> y = 384
> colours = ["ff0000", "00ff00", "0000ff"]
> img = RippedImage.new(1, x, y)
> (x*y).times do
>  img.draw(colours[rand(colours.length)])
> end
> img.finalize

are you really limited to using string pixel values?  if not i would say you
should be able to generate these images in __way__ under 1s.  even if you are,
using import_pixels will be tons faster:

your original:

     jib:~/eg/ruby > time ruby a.rb

     real    0m4.028s
     user    0m3.620s
     sys     0m0.070s


using import_pixels:


   jib:~/eg/ruby > time ruby a.rb

   real    0m0.829s
   user    0m0.810s
   sys     0m0.000s


   jib:~/eg/ruby > cat a.rb
   require 'rubygems'
   require 'RMagick'
   class RippedImage
     LITTLE_ENDIAN = [42].pack('i').unpack('c').first.nonzero? ? true : false
     BIG_ENDIAN = ! LITTLE_ENDIAN
     MAP = BIG_ENDIAN ? 'ARGB' : 'BGRA'
     def initialize width, height
       @width = Integer width
       @height = Integer height
       @pixels  = []
     end
     def << c
       @pixels << c.hex
       self
     end
     def draw path
       img = Magick::Image.new @width, @height
       img.import_pixels 0, 0, @width, @height, MAP, @pixels.pack('i*'), Magick::CharPixel
       img.opacity = 255  # because the pack leaves it 0 - totally transparent
       img.write path
     end
   end

   x = 512
   y = 384
   colours = ["ff0000", "00ff00", "0000ff"]
   img = RippedImage.new x, y
   (x*y).times{ img << (colours[rand(colours.length)]) }
   img.draw "#{ 1 }.png"


so that's a four times speed-up right there.  i suspect 1s is a reasonable
number too.


kind regards.


-a
-- 
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama