## [Vxl-maintainers] vipl_gaussian_convolution uses poor mask

 [Vxl-maintainers] vipl_gaussian_convolution uses poor mask From: Ian Scott - 2002-05-31 18:20:18 The mask creation in vipl_gaussian_convolution doesn't look correct to me. For a start, Purify is complaining about a bounds error on line 69 http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/vxl/vxl/tbl/vipl/vipl_gaussia n_convolution.txx?annotate=HEAD#69 I think the for condition on the previous line should probably by x

 [Vxl-maintainers] vipl_gaussian_convolution uses poor mask From: Ian Scott - 2002-05-31 18:20:18 The mask creation in vipl_gaussian_convolution doesn't look correct to me. For a start, Purify is complaining about a bounds error on line 69 http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/vxl/vxl/tbl/vipl/vipl_gaussia n_convolution.txx?annotate=HEAD#69 I think the for condition on the previous line should probably by x
 Re: [Vxl-maintainers] vipl_gaussian_convolution uses poor mask From: Peter Vanroose - 2002-06-01 00:14:50 > existing delta mask 0.3989 0.2420 0.0540 0.0044 0.0001 > alternative integral mask 0.4420 0.1331 0.0709 0.0448 0.0302 I agree with your remark: values should indeed be integrals of the Gauss curve between x-0.5 and x+0.5 (for x=0,1,2...) But I don't agree with your numbers: I believe the correct values (for sigma=1) should be: 0.38292 0.24173 0.06060 0.005977 0.000229 which are: $\int_{-0.5}^{0.5} exp(-x*x/2) dx$, $\int_{0.5}^{1.5} ...$ or: erf(0.5/sqrt(2)), 0.5*(erf(1.5/sqrt(2))-erf(0.5/sqrt(2)), ... I have now (for the time being) replaced the implementation by using a 16-piece trapezoid appoximation of the integral between x-0.5 and x+0.5. The obtained values are very close to the ones above. Peter.