This ImageJ plugin-filter processes images of differential interference contrast microscopy (DIC) of sparse objects on a uniform background. It converts a differentiated image (seemingly illuminated from the side), with one side darker and one brighter than the background, into an image where the objects stand out as a bright (or dark) entities.

The image has to be converted to 32 bits (Image>Type>32-bits).

The plugin only works if the gradients are in the horizontal (x) direction; either have the DIC set up oriented accordingly or rotate the image. Before rotating the image, apply a highpass filter.

For good results, dark spots from dust in the optics or on the camera sensor should be avoided. If necessary, apply dark frame and flat field corrections to the image.

The plugin does three steps:

1. High-pass filter in x direction, may be deselected if a high-pass filter has been applied to the image before (put the sigma to 0).
2. Integration along the image lines.
3. High-pass filter in x direction.

Instead of the second high-pass filter, it would be better to apply a 1D 'sliding paraboloid' background subtraction; this would avoid the dark background strips left&right of the objects (but I did not have time to implement it). With the current version, you have to play with the smoothing parameters to reduce these artifacts.

Download the source code or .class file and rename to DIC_Processor.java or DIC_Processor.class, respectively. Uppercase/lowercase matters. Put in to the ImageJ/plugins directory or an immediate subdirectory thereof.

2020-Feb-28 1st version.

Source code, for 'Compile & Run' on ImageJ 1.
.class file, if 'Compile & Run' does not work (ImageJ2).

Public domain. This plugin is provided on an “AS IS” BASIS and WITHOUT WARRANTY.

Michael Schmid