Finally I figure out the problem with the convolve method. The code I wrote was only prepared to deal with TYPE_INT_ARGB BufferedImages but when reading a image from a file, it doesn’t ensure this type. Now this is fixed and working.
Furthermore, I added charcoal, solarize and shade effects. The latter gave some problem while testing, but finally the problem was in test not in code. From now on, the to_threshold method must be used in test when dealing with numbers that depend on the QuantumRange. This problem is due that QuantumRange can differ from one ImageMagick installation to another, but RMagick4J always uses 255.
Here you are some examples (the guy that looks like me is actually my non-existent twin brother):
|RMagick||RMagick4J (This is what I do)|
|charcoal 0.75 (RMagick4J is not normalized)|
|shade true, 50, 50|