There are lots of image segmentation techniques. First you have to decide what kind of image segmentation you have to do. For instance: if you need only just background reduction you can go through for any algorithm like watershed(openCV python image Processing) of some kinds which you can find in the MATWorks. also if you need for Edge Detection you can go through In Improve Canny algorithm(python) where you can find histogram(RGB color segment) also. And Finally if you need to analyze some thousands of images with segmentation with other special features you can go through with Machine Learning(ML) K-means clustering algorithm.
I guess the best and easiest segmentation method is the Self-Organizing maps (SOMs). It can be implemented easily in MATLAB and you can find many MATLAB source code for this type of problem. In addition, it is unsupervised and requires no guidance or interference.
I know that thresholding method is the simplest segmentation techniques, for medical images ITK-Snap is very easy to use stand alone software. also ImageJ and fiji have many segmentation tools for many images format I think there are more easier and user friendly than MATLAB