If I understood correctly (and this page should confirm: http://www.cs.ioc.ee/~khoros2/linear/convolution-teo/front-page.html)
if I convolve linearly (the usual point-to-point multiplication and addition without tricks for each element of the image matrix) an image with a kernel I obtain RESULT1
if I calculate the DFT of the image and of the padded kernel (to have same size as the image) and perform their multiplication in frequency and then the inverse DFT, the result is RESULT2 and should be like applying the circular convolution in time space
RESULT1 slightly differs from RESULT2 as in the example
Is this correct?