You might possibly be asking for findpeaks(). Or you might possibly be asking for http://www.mathworks.com/help/images/ref/imregionalmax.html. Or perhaps you are looking for http://www.mathworks.com/help/vision/ref/vision.localmaximafinder.step.html . Or maybe http://www.mathworks.com/help/wavelet/ref/localmax.html. Or you could use http://www.mathworks.com/help/images/ref/imdilate.html and http://www.mathworks.com/help/images/ref/imerode.html
My crystal ball is predicting that you are doing histogram equalization and that what you need is mode after quantizing the values.
