text: var ConvolutionFilter = require('./convolution');
  
  function SharpenFilter(radius) {
      ConvolutionFilter.apply(this, Array.prototype.slice.call(arguments));
  }
  SharpenFilter.prototype = Object.create(ConvolutionFilter.prototype);
  SharpenFilter.prototype.constructor = SharpenFilter;
  SharpenFilter.prototype.initKernel = function() {
      this.kernel = [-1, -1, -1,
      -1,  9, -1,
      -1, -1, -1];
      this.divisor = 1;
  };
  
  module.exports = SharpenFilter;
  