possible long time bug with -fft in IM 6.5.x to 6.6.x

[magick]

Download load the ImageMagick source and type:

• cd ImageMagick-6.6.7-7
  ./configure
  make
  make install
  make check

The 'make check' runs the validation test.

[fmw42]

The magnitude, phase, and spectrum images seem OK, but the mask is always almost black

try writing intermediate images and see if they match mine below to see which command is the problem:


convert clown_spectrum_edited.png clown_spectrum.png \
-compose difference -composite -write clown_tmp1.png \
-threshold 0 -write clown_tmp2.png -negate clown_spectrum_mask.png


clown_tmp1.png


clown_tmp2.png



Also as the PNG coder has been changing over the last number of releases, you could try prefacing each write or output image with PNG32:

convert clown_spectrum_edited.png clown_spectrum.png \
-compose difference -composite -write PNG32:clown_tmp1.png \
-threshold 0 -write PNG32:clown_tmp2.png -negate PNG32:clown_spectrum_mask.png

See if that makes a difference.