Codebrawl #10

output.png

solution.rb

#!/usr/bin/env ruby

require 'chunky_png'

# Convert the RGB coordinates to polar form (HSV) and get the hue.
# Formula from: http://en.wikipedia.org/wiki/Hue#Computing_hue_from_RGB
# Doesn't handle all the cases (R >= B > G, for example), but it gets the job done.
def get_hue(r,g,b)
	max = [r,g,b].max
	if max == r
		hue = 0.0 + 60.0 * (g - b)
		if(hue < 0.0)
			hue += 360.0
		end
	elsif max == g
		hue = 120.0 + 60.0 * (b-r)
	else
		hue= 240+60*(r-g)
	end
	return hue
end

image = ChunkyPNG::Image.from_file('input.png')

# The hue of the color we want to select
color = 204
req_range = color-34..color+34

# Iterate over the pixels in the image.
# If the hue for the pixel is NOT in the required range, convert that pixel to grayscale.
# The required range is 20 degrees +/- a single hue.
# Here blue has hue of 240, so our range is 220 -> 260.
for i in 0...image.width
	for j in 0...image.height
		pixel = image.get_pixel(i,j)

		r = ChunkyPNG::Color.r(pixel).to_f
		g = ChunkyPNG::Color.g(pixel).to_f
		b = ChunkyPNG::Color.b(pixel).to_f

		hue = get_hue(r/255,g/255,b/255) # Convert co-ordinates to be between 0 and 1

		if not req_range.include?(hue)
			image.set_pixel(i,j,ChunkyPNG::Color.to_grayscale(pixel))
		end
	end
end

image.save('output.png')

Doesn't that mean that only I can view this gist?

I'm quite sure you can submit a Private one. You need to connect your GitHub account to Codebrawl.

Alternatively, check with https://github.com/jeffkreeftmeijer

All right, I will check. Thanks for the heads up!