[GitHub] eli2014 commented on issue #12403: roi_align.cc bug?

[GitBox <gi...@apache.org>]

eli2014 commented on issue #12403: roi_align.cc bug?
URL: https://github.com/apache/incubator-mxnet/issues/12403#issuecomment-425300969
 
 
   @yuxihu @apeforest 
   I made a mistake in the example. The value of spatial_scale should be 1.0. 
   So the statement 'mx.nd.ROIAlign(x, y, (2, 2), 0.7)' should be 'mx.nd.ROIAlign(x, y, (2, 2), 1.0)'.
   If you rerun the example, the output will be 
   [[[[5.25, 6.75],
   [14.25, 15.75]]]].
   
   I think the output should be
   [[[[3,5, 5.5],
   [15.5, 17.5]]]]
   
   Because y = mx.nd.array([[0,0,0,3,3]]) means the start coordinate is (0, 0) and the end coordinate is (3, 3).
   The RoI is
   [ 0., 1., 2., 3.],
   [ 6., 7., 8., 9.],
   [ 12., 13., 14., 15.],
   [ 18., 19., 20., 21.]
   
   Since pooled_size = (2, 2),  and both of the height and width of RoI are 4, which can be divisible by pooled_size. 
   According to the description of ROIAlign, we can compute the each value of the output, for example,
   3.5 = (0 + 1 + 6 + 7) / 4,  and so on.
   
   

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