I'm trying to implement Gaussian blur to the gray image. But I do find that there are differences between the output of Gaussian blur process of GIMP and mine.
As you can see the above images, the left is the output of GIMP and right image is mine. and GIMP's image is more fine.
I used 7x7 horizontal and vertical blur radius of GIMP Gaussian at left image. and right image made by 7x7 Gaussian blur coefficients .
A00 = 0.000036; A01 = 0.000363; A02 = 0.001446; A03 = 0.002291; A04 = 0.001446; A05 = 0.000363; A06 = 0.000036;
A10 = 0.000363; A11 = 0.003676; A12 = 0.014662; A13 = 0.023226; A14 = 0.014662; A15 = 0.003676; A16 = 0.000363;
A20 = 0.001446; A21 = 0.014662; A22 = 0.058488; A23 = 0.092651; A24 = 0.058488; A25 = 0.014662; A26 = 0.001446;
A30 = 0.002291; A31 = 0.023226; A32 = 0.092651; A33 = 0.146768; A34 = 0.092651; A35 = 0.023226; A36 = 0.002291;
A40 = 0.001446; A41 = 0.014662; A42 = 0.058488; A43 = 0.092651; A44 = 0.058488; A45 = 0.014662; A46 = 0.001446;
A50 = 0.000363; A51 = 0.003676; A52 = 0.014662; A53 = 0.023226; A54 = 0.014662; A55 = 0.003676; A56 = 0.000363;
A60 = 0.000036; A61 = 0.000363; A62 = 0.001446; A63 = 0.002291; A64 = 0.001446; A65 = 0.000363; A66 = 0.000036;
pBlurData[i*rwsize + j] =
A00*(double)pTempData[(i - 3)*rwsize + j - 3] + A01*(double)pTempData[(i - 3)*rwsize + j - 2] + A02*(double)pTempData[(i - 3)*rwsize + j - 1] + A03*(double)pTempData[(i - 3)*rwsize + j] + A04*(double)pTempData[(i - 3)*rwsize + j + 1] + A05*(double)pTempData[(i - 3)*rwsize + j + 2] + A06*(double)pTempData[(i - 3)*rwsize + j + 3]
+ A10*(double)pTempData[(i - 2)*rwsize + j - 3] + A11*(double)pTempData[(i - 2)*rwsize + j - 2] + A12*(double)pTempData[(i - 2)*rwsize + j - 1] + A13*(double)pTempData[(i - 2)*rwsize + j] + A14*(double)pTempData[(i - 2)*rwsize + j + 1] + A15*(double)pTempData[(i - 2)*rwsize + j + 2] + A16*(double)pTempData[(i - 2)*rwsize + j + 3]
+ A20*(double)pTempData[(i - 1)*rwsize + j - 3] + A21*(double)pTempData[(i - 1)*rwsize + j - 2] + A22*(double)pTempData[(i - 1)*rwsize + j - 1] + A23*(double)pTempData[(i - 1)*rwsize + j] + A24*(double)pTempData[(i - 1)*rwsize + j + 1] + A25*(double)pTempData[(i - 1)*rwsize + j + 2] + A26*(double)pTempData[(i - 1)*rwsize + j + 3]
+ A30*(double)pTempData[(i + 0)*rwsize + j - 3] + A31*(double)pTempData[(i + 0)*rwsize + j - 2] + A32*(double)pTempData[(i + 0)*rwsize + j - 1] + A33*(double)pTempData[(i + 0)*rwsize + j] + A34*(double)pTempData[(i + 0)*rwsize + j + 1] + A35*(double)pTempData[(i + 0)*rwsize + j + 2] + A36*(double)pTempData[(i + 0)*rwsize + j + 3]
+ A40*(double)pTempData[(i + 1)*rwsize + j - 3] + A41*(double)pTempData[(i + 1)*rwsize + j - 2] + A42*(double)pTempData[(i + 1)*rwsize + j - 1] + A43*(double)pTempData[(i + 1)*rwsize + j] + A44*(double)pTempData[(i + 1)*rwsize + j + 1] + A45*(double)pTempData[(i + 1)*rwsize + j + 2] + A46*(double)pTempData[(i + 1)*rwsize + j + 3]
+ A50*(double)pTempData[(i + 2)*rwsize + j - 3] + A51*(double)pTempData[(i + 2)*rwsize + j - 2] + A52*(double)pTempData[(i + 2)*rwsize + j - 1] + A53*(double)pTempData[(i + 2)*rwsize + j] + A54*(double)pTempData[(i + 2)*rwsize + j + 1] + A55*(double)pTempData[(i + 2)*rwsize + j + 2] + A56*(double)pTempData[(i + 2)*rwsize + j + 3]
+ A60*(double)pTempData[(i + 3)*rwsize + j - 3] + A61*(double)pTempData[(i + 3)*rwsize + j - 2] + A62*(double)pTempData[(i + 3)*rwsize + j - 1] + A63*(double)pTempData[(i + 3)*rwsize + j] + A64*(double)pTempData[(i + 3)*rwsize + j + 1] + A65*(double)pTempData[(i + 3)*rwsize + j + 2] + A66*(double)pTempData[(i + 3)*rwsize + j + 3];
I've got theses values from http://dev.theomader.com/gaussian-kernel-calculator/
But there are difference the output of the processing.
What sigma value used in GIMP to Gaussian blur?
