Information about the watershed method

The watershed method helps to segment images. Now in my project the segmentation is not perfect. I wondered if this would be the result of using the watershed methode. the intensities in my image (of many many cells close to each other) differs in everyframe. Therefor I wonder if the same happens at the image on the right with the standard matlab function. I do not use the marker controlled watershed method. Does anyone have any documentation about this?