#!/home/software/ruby-1.8.5/bin/ruby -w require 'RMagick' # Demonstrate partial transparency and the get_pixels and # store_pixels methods by creating an image that goes from # full-color on the left to monochrome on the right. # Read the colorful picture of a rock formation. Scale # it to 300 pixels high because we don't want a big picture. rocks = Magick::Image.read('images/Red_Rocks.jpg').first rocks.scale!(250.0/rocks.rows) # Make a monochrome copy. See Image#quantize for details grayrocks = rocks.quantize(256, Magick::GRAYColorspace) rows = grayrocks.rows cols = grayrocks.columns # Create an array of opacity values, proceeding from # transparent to opaque. The array should have as many # elements as there are columns in the image. The first # element should be TransparentOpacity and each succeeding # element slightly more opaque than its predecessor. step = Magick::TransparentOpacity / cols.to_f opacity_steps = Array.new(cols) cols.times { |x| opacity_steps[x] = Magick::TransparentOpacity - Integer(x * step) if opacity_steps[x] < Magick::OpaqueOpacity opacity_steps[x] = Magick::OpaqueOpacity end } # Get each row of pixels from the mono image. # Copy the pre-computed opacity values to the pixels. # Store the pixels back. rows.times { |y| pixels = grayrocks.get_pixels(0, y, cols, 1) pixels.each_with_index { |p,x| p.opacity = opacity_steps[x] } grayrocks.store_pixels(0, y, cols, 1, pixels) } # Composite the mono version of the image over the color version. grayrocks.matte = true combine = rocks.composite(grayrocks, Magick::CenterGravity, Magick::OverCompositeOp) #combine.display combine.write 'get_pixels.jpg' exit