This function performs binary erosion or dilation.

It is faster than imerode.m and imdilate.m -- by more than an order of magnitude for any structuring element other than 'square' or 'disk' .
The only time it is slightly slower (about 10%) is for very small 'square' or 'disk' strels only.
Moreover, ’disk’ structuring elements in Matlab are actually octagonal, and often times a
true ’circular’ element is necessity.

It also comes in very handy when you don't have the Matlab Image Processing Toolbox :-)...

The function also allows very fast iterative calls which re-use the work done at previous iterations. (for instance when sweeping the size/size+shape of the structuring element while looking for a certain effect, a threshold in image statistics, etc.)
This re-use will make the speed increase compound exponentially, and one can also break the execution when desired.

For 2-3M pix images and strels in the range of 10-20 pixels the speed increase can be around 20x - 100x (depending on the machine cache, slightly on strel shape, etc.), with higher values as the image and/or strel size increase.

Simple call:
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IMG_OUT = BMORPH(IMG_IN, SE, DilateNotErode, [], ObjStopAtEdge)

IMG_DIL = BMORPH(IMG_IN, SE, true); % dilate
IMG_ERO = BMORPH(IMG_IN, SE, false); % erode
% erode assuming the objects stop at edge :
IMG_ERO = BMORPH(IMG_IN, SE, false, [], true);

For iterative calls and more info on execution speed see the help in bmorph.m and the attached .pdf file.