module ChunkyPNG::Canvas::Resampling
The ChunkyPNG::Canvas::Resampling
module defines methods to perform image resampling to a {ChunkyPNG::Canvas}.
Currently, only the nearest neighbor algorithm is implemented. Bilinear and cubic algorithms may be added later on.
@see ChunkyPNG::Canvas
Public Instance Methods
# File lib/chunky_png/canvas/resampling.rb 134 def resample_bilinear(new_width, new_height) 135 dup.resample_bilinear!(new_width, new_height) 136 end
Resamples the canvas with bilinear interpolation. @param [Integer] new_width The width of the resampled canvas. @param [Integer] new_height The height of the resampled canvas. @return [ChunkyPNG::Canvas] A new canvas instance with the resampled pixels.
# File lib/chunky_png/canvas/resampling.rb 98 def resample_bilinear!(new_width, new_height) 99 index_x, interp_x = steps_residues(width, new_width) 100 index_y, interp_y = steps_residues(height, new_height) 101 102 pixels = Array.new(new_width * new_height) 103 i = 0 104 for y in 1..new_height 105 # Clamp the indicies to the edges of the image 106 y1 = [index_y[y - 1], 0].max 107 y2 = [index_y[y - 1] + 1, height - 1].min 108 y_residue = interp_y[y - 1] 109 110 for x in 1..new_width 111 # Clamp the indicies to the edges of the image 112 x1 = [index_x[x - 1], 0].max 113 x2 = [index_x[x - 1] + 1, width - 1].min 114 x_residue = interp_x[x - 1] 115 116 pixel_11 = get_pixel(x1, y1) 117 pixel_21 = get_pixel(x2, y1) 118 pixel_12 = get_pixel(x1, y2) 119 pixel_22 = get_pixel(x2, y2) 120 121 # Interpolate by Row 122 pixel_top = ChunkyPNG::Color.interpolate_quick(pixel_21, pixel_11, x_residue) 123 pixel_bot = ChunkyPNG::Color.interpolate_quick(pixel_22, pixel_12, x_residue) 124 125 # Interpolate by Column 126 127 pixels[i] = ChunkyPNG::Color.interpolate_quick(pixel_bot, pixel_top, y_residue) 128 i += 1 129 end 130 end 131 replace_canvas!(new_width.to_i, new_height.to_i, pixels) 132 end
# File lib/chunky_png/canvas/resampling.rb 90 def resample_nearest_neighbor(new_width, new_height) 91 dup.resample_nearest_neighbor!(new_width, new_height) 92 end
Resamples the canvas using nearest neighbor interpolation. @param [Integer] new_width The width of the resampled canvas. @param [Integer] new_height The height of the resampled canvas. @return [ChunkyPNG::Canvas] A new canvas instance with the resampled pixels.
# File lib/chunky_png/canvas/resampling.rb 74 def resample_nearest_neighbor!(new_width, new_height) 75 steps_x = steps(width, new_width) 76 steps_y = steps(height, new_height) 77 78 pixels = Array.new(new_width * new_height) 79 i = 0 80 for y in steps_y 81 for x in steps_x 82 pixels[i] = get_pixel(x, y) 83 i += 1 84 end 85 end 86 87 replace_canvas!(new_width.to_i, new_height.to_i, pixels) 88 end
Integer Interpolation between two values
Used for generating indicies for interpolation (eg, nearest neighbour).
@param [Integer] width The width of the source @param [Integer] new_width The width of the destination @return [Array<Integer>] An Array of Integer indicies
# File lib/chunky_png/canvas/resampling.rb 21 def steps(width, new_width) 22 indicies, residues = steps_residues(width, new_width) 23 24 for i in 1..new_width 25 indicies[i - 1] = (indicies[i - 1] + (residues[i - 1] + 127) / 255) 26 end 27 indicies 28 end
Fractional Interpolation between two values
Used for generating values for interpolation (eg, bilinear). Produces both the indices and the interpolation factors (residues).
@param [Integer] width The width of the source @param [Integer] new_width The width of the destination @return [Array<Integer>, Array<Integer>] Two arrays of indicies and residues
# File lib/chunky_png/canvas/resampling.rb 38 def steps_residues(width, new_width) 39 indicies = Array.new(new_width, nil) 40 residues = Array.new(new_width, nil) 41 42 # This works by accumulating the fractional error and 43 # overflowing when necessary. 44 45 # We use mixed number arithmetic with a denominator of 46 # 2 * new_width 47 base_step = width / new_width 48 err_step = (width % new_width) << 1 49 denominator = new_width << 1 50 51 # Initial pixel 52 index = (width - new_width) / denominator 53 err = (width - new_width) % denominator 54 55 for i in 1..new_width 56 indicies[i - 1] = index 57 residues[i - 1] = (255.0 * err.to_f / denominator.to_f).round 58 59 index += base_step 60 err += err_step 61 if err >= denominator 62 index += 1 63 err -= denominator 64 end 65 end 66 67 [indicies, residues] 68 end