Image Warp

Images can be warped using vector fields.  The warp vectors are indicating the location of the source pixel.  The code warps an equirectangular projection on an azimuthal projection.

#!/usr/bin/env ruby
require 'hornetseye'
include Hornetseye
raise "Syntax: warp.rb <input file> <output file>" if ARGV.size != 2
class MultiArray
  class << self
    def ramp( w, h )
      idx = int( w, h ).indgen!
      retval = MultiArray.int 2, w, h
      retval.roll[ 0 ] = idx % w
      retval.roll[ 1 ] = idx / w
      retval
    end
  end
end
img = MultiArray.load_ubytergb( ARGV[0] ).downsample [ 2, 2 ], [ 1, 1 ]
w, h = img.shape[0], img.shape[1]
c = 0.5 * h
r = MultiArray.ramp h, h
x, y = r.roll[ 0 ], r.roll[ 1 ]
warp = MultiArray.int 2, h, h
warp.roll[ 0 ] = ( Math.atan2( x - c, y - c ) / Math::PI + 1 ) * w / 2 - 0.5
warp.roll[ 1 ] = Math.hypot( x - c, y - c )
result = MultiArray.ubytergb( w + h + 1, h )
result.roll[    0 ...     w  ] = img
result.roll[    w ...  (w+1) ] = RGB 0xFF, 0x00, 0x00
result.roll[ (w+1)...(w+h+1) ] = img.warp_clipped warp
result.save_ubytergb ARGV[1]
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