Shadows Op

[gselzer]

This Op provides an Op version of the ImageJ Core Plugin created by Barry Dezonia.

Below is a demo of the new Shadows Op (middle) run on this image (left), taken from imagej.net, alongside the output of the same image run through the Plugin (right).

Points of Discussion:

• As of now the Op generates its Shadows kernel through the used of an angle Parameter, allowing for a single Op as opposed to the eight different Plugins that already exist. The use of an angle parameter also allows the user to generate shadows at any desired angle instead of being limited to the eight predefined angles. The only downside to this is that in order to keep the algorithm simple the Op uses sine and cosine values to generate the kernel which differs from the linear kernel of the older Plugins, resulting in differing outputs (though in most cases not visually distinguishable). Is it okay that the Op differ from the Plugin it adapts in order to increase its flexibility?

TODO:

• Write a test for the Op. The above point should be decided on before a test is written. If we decide that the difference in output should be allowed then a simple Regression test can be created, otherwise we could test the Op based on the output of the Plugin if we deem it necessary to make the output exactly the same.

[ctrueden]

I am OK with the output differing from past implementations, so that we achieve a configurable angle.

Please write a test, and then we can merge it.

[gselzer]

@ctrueden I found test commit that was for some reason not pushed. The test passes and is sound, however it introduces a test-scope dependency on scijava-io-http that I am not sure we want. It also forces the download of abe.tif, which seems bad to me. However it does have a method downloadOnce that seems valuable; maybe it should go in DownloadService. Let me know what you think of this