67 lines
2.0 KiB
Racket
67 lines
2.0 KiB
Racket
#lang planet dyoo/whalesong/base
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(require (planet dyoo/whalesong/resource)
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(planet dyoo/whalesong/image))
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;; The Iron Image Puzzle
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;; Part of the Nifty Assignments page by Nick Parlante.
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;; http://nifty.stanford.edu/2011/parlante-image-puzzle/
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;; To run this program locally on your machine under Google Chrome, you'll
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;; probably need to use --allow-file-access-from-files to get around
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;; the same-origin policy. The program should run normally if served on
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;; a web server
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(define-resource iron-puzzle.png)
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;; First, grab the image by its url.
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(define distorted-image iron-puzzle.png)
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distorted-image
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(image-width distorted-image)
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(image-height distorted-image)
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;; We will want to decompose the image into its individual pixels. We can use
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;; image->color-list to do this.
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;; To make experimenting with the pixels an easy thing to do, let?s write
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;; a function that will let us ?map? across the pixels of an image
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;; to get another image.
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(define (image-transform an-image a-pixel-transform)
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(local [(define colors (image->color-list an-image))
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(define new-colors (map a-pixel-transform colors))]
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(color-list->image new-colors
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(image-width an-image)
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(image-height an-image)
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0
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0)))
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;; With image-transform in hand, we can apply a filter,
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;; such as zeroing out the blue and green components like this:
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(define (zero-blue-green a-color)
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(make-color (color-red a-color)
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0
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0))
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(define dark-image
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(image-transform distorted-image zero-blue-green))
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dark-image
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;; The image is still a bit darkened. Let?s bump up the red component
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;; by a factor of ten.
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(define (red*10 a-color)
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(make-color (* (color-red a-color) 10)
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(color-green a-color)
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(color-blue a-color)))
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(define red-eye-image
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(image-transform dark-image red*10))
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;; And now we should be able to look at red-eye-image and recognize
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;; the landmark.
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red-eye-image
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(image-width red-eye-image)
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(image-height red-eye-image)
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