code: public static GrayF64 convolve(GrayF64 integral ,
  								   IntegralKernel kernel ,
  								   GrayF64 output )
  	{
  		output = InputSanityCheck.checkDeclare(integral,output);
  
  		if(BoofConcurrency.USE_CONCURRENT) {
  			ImplIntegralImageConvolve_MT.convolve(integral, kernel, output);
  		} else {
  			ImplIntegralImageConvolve.convolve(integral, kernel, output);
  		}
  
  		return output;
  	}
docs: General code for convolving a box filter across an image using the integral image.
  
  @param integral Integral image.
  @param kernel Convolution kernel.
  @param output The convolved image. If null a new image will be declared and returned. Modified.
  @return Convolved image.