Module ChunkyPNG::Canvas::Adam7Interlacing
In: lib/chunky_png/canvas/adam7_interlacing.rb

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.

Methods

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.

[Source]

    # File lib/chunky_png/canvas/adam7_interlacing.rb, line 57
57:       def adam7_extract_pass(pass, canvas)
58:         x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
59:         sm_pixels = []
60:         
61:         y_offset.step(canvas.height - 1, 1 << y_shift) do |y|
62:           x_offset.step(canvas.width - 1, 1 << x_shift) do |x|
63:             sm_pixels << canvas[x, y]
64:           end
65:         end
66:         
67:         new_canvas_args = adam7_pass_size(pass, canvas.width, canvas.height) + [sm_pixels]
68:         ChunkyPNG::Canvas.new(*new_canvas_args)
69:       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

[Source]

    # File lib/chunky_png/canvas/adam7_interlacing.rb, line 42
42:       def adam7_merge_pass(pass, canvas, subcanvas)
43:         x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
44:         for y in 0...subcanvas.height do
45:           for x in 0...subcanvas.width do
46:             new_x = (x << x_shift) | x_offset
47:             new_y = (y << y_shift) | y_offset
48:             canvas[new_x, new_y] = subcanvas[x, y]
49:           end
50:         end
51:       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.

[Source]

    # File lib/chunky_png/canvas/adam7_interlacing.rb, line 14
14:       def adam7_multiplier_offset(pass)
15:         [3 - (pass >> 1), (pass & 1 == 0) ? 0 : 8 >> ((pass + 1) >> 1),
16:          pass == 0 ? 3 : 3 - ((pass - 1) >> 1), (pass == 0 || pass & 1 == 1) ? 0 : 8 >> (pass >> 1)]
17:       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.

[Source]

    # File lib/chunky_png/canvas/adam7_interlacing.rb, line 23
23:       def adam7_pass_size(pass, original_width, original_height)
24:         x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
25:         [ (original_width  - x_offset + (1 << x_shift) - 1) >> x_shift,
26:           (original_height - y_offset + (1 << y_shift) - 1) >> y_shift]
27:       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

[Source]

    # File lib/chunky_png/canvas/adam7_interlacing.rb, line 34
34:       def adam7_pass_sizes(original_width, original_height)
35:         (0...7).map { |pass| adam7_pass_size(pass, original_width, original_height) }
36:       end

[Validate]