Apps similar to Image Pro include ImageJ, which is free and open source. Other options are Fiji, Icy Image Processing and MIPAR. In total there are four Image Editors like Image Pro for Mac, Windows and Linux.
ImageJ is a public domain, Java-based image processing program developed at the National Institutes of Health. ImageJ was designed with an open architecture that provides extensibility via Java plugins and recordable macros.
Fiji is an image processing package—a "batteries-included" distribution of ImageJ, bundling a lot of plugins which facilitate scientific image analysis.
User-friendly, research-grade software to acquire, visualise and quantify 2D to 5D biological (microscopy) images
France
EU
MIPAR is a revolutionary image analysis software, capable of identifying and measuring features from nearly any image one can capture.
