A plugin-filter providing a highpass command. It subtracts the Gaussian blurred input image from the input image.

• Radius (Sigma) is the standard deviation (blur length) of the Gaussian that will be subtracted.

• Scaled Units (spatially calibrated images only) should be selected if “Radius (Sigma)” is not in pixels but in physical units (e.g., micrometers).

• Shift Values to Display Range adds an offset so that the output will fit into the currently displayed data range. This option should be selected when processing only a selection of a 32-bit (float) image that does not have its pixel values around zero. This option is also useful for most 16-bit images.

• Preview is available with the Preview checkbox.

If “Shift Values to Display Range” is unchecked, the offset, i.e. the output created by flat portions of the image, will be 0 for 32-bit float, 32768 for 16-bit and 128 for 8-bit (grayscale or RGB) images.

If the full image is processed, for grayscale 8-bit and 16-bit images, the grayscale (pixel value) calibration will be set to have zero value at this level. Thus, one can use, e.g., Process>Math>Square after high-pass filtering to highlight all pixels deviating from their surrounding.

Note that Undo will revert only the image contents, not the calibration.

• Download the sourcecode (file High_pass.java), put it into the ImageJ/plugins directory or an immediate subdirectory thereof. Make sure you name the downloaded file ”High_pass.java”; uppercase/lowercase matters.
• Compile it via Plugins>Compile and Run…
• Alternatively, directly save the .class file High_pass.class into the ImageJ/plugins directory or an immediate subdirectory thereof. Again, make sure that you name the file correctly, uppercase/lowercase matters.

— Michael Schmid 2007/06/28 15:12