module ChunkyPNG::Canvas::Adam7Interlacing
Methods for decoding and encoding Adam7 interlacing.
Adam7 interlacing extracts 7 pass images out of a single image, that can be encoded to a stream separately so the image can be built up progressively. The module is included into ChunkyPNG
canvas and is used to extract the pass images from the original image, or to reconstruct an original image from separate pass images.
Public Instance Methods
Extracts a pass from a complete image @param [Integer] pass The pass number, should be in 0..6. @param [ChunkyPNG::Canvas] canvas The image that is being deconstructed. @return [ChunkyPNG::Canvas] The extracted pass image.
# File lib/chunky_png/canvas/adam7_interlacing.rb 63 def adam7_extract_pass(pass, canvas) 64 x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass) 65 sm_pixels = [] 66 67 y_offset.step(canvas.height - 1, 1 << y_shift) do |y| 68 x_offset.step(canvas.width - 1, 1 << x_shift) do |x| 69 sm_pixels << canvas[x, y] 70 end 71 end 72 73 new_canvas_args = adam7_pass_size(pass, canvas.width, canvas.height) + [sm_pixels] 74 ChunkyPNG::Canvas.new(*new_canvas_args) 75 end
Merges a pass image into a total image that is being constructed. @param [Integer] pass The pass number, should be in 0..6. @param [ChunkyPNG::Canvas] canvas The image that is being constructed. @param [ChunkyPNG::Canvas] subcanvas The pass image that should be merged
# File lib/chunky_png/canvas/adam7_interlacing.rb 48 def adam7_merge_pass(pass, canvas, subcanvas) 49 x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass) 50 for y in 0...subcanvas.height do 51 for x in 0...subcanvas.width do 52 new_x = (x << x_shift) | x_offset 53 new_y = (y << y_shift) | y_offset 54 canvas[new_x, new_y] = subcanvas[x, y] 55 end 56 end 57 end
Returns an array with the x-shift, x-offset, y-shift and y-offset for the requested pass. @param [Integer] pass The pass number, should be in 0..6.
# File lib/chunky_png/canvas/adam7_interlacing.rb 14 def adam7_multiplier_offset(pass) 15 [ 16 3 - (pass >> 1), 17 pass & 1 == 0 ? 0 : 8 >> ((pass + 1) >> 1), 18 pass == 0 ? 3 : 3 - ((pass - 1) >> 1), 19 pass == 0 || pass & 1 == 1 ? 0 : 8 >> (pass >> 1), 20 ] 21 end
Returns the pixel dimensions of the requested pass. @param [Integer] pass The pass number, should be in 0..6. @param [Integer] original_width The width of the original image. @param [Integer] original_height The height of the original image.
# File lib/chunky_png/canvas/adam7_interlacing.rb 27 def adam7_pass_size(pass, original_width, original_height) 28 x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass) 29 [ 30 (original_width - x_offset + (1 << x_shift) - 1) >> x_shift, 31 (original_height - y_offset + (1 << y_shift) - 1) >> y_shift, 32 ] 33 end
Returns an array of the dimension of all the pass images. @param [Integer] original_width The width of the original image. @param [Integer] original_height The height of the original image. @return [Array<Array<Integer>>] Returns an array with 7 pairs of dimensions. @see adam7_pass_size
# File lib/chunky_png/canvas/adam7_interlacing.rb 40 def adam7_pass_sizes(original_width, original_height) 41 (0...7).map { |pass| adam7_pass_size(pass, original_width, original_height) } 42 end