Rule 30 by tabasa

((r="  "+gets.chomp+"  ").length-2).times{|i|putc(((n=(r[i]-32)/3*4+(r[i+1]-32)/3*2+(r[i+2]-32)/3)>0&&n<5)?'#':' ')}

Note that non-ascii characters in the above source code will be escaped (such as \x9f).

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