mmdcalc
Extract the keys of a calculator.

The gray-scale image of the calculator is read.

a = mmreadgray('keyb.tif');

mmshow(a);

a

The image edges are enhanced by the gradient operator.

b = mmgradm(a, mmsebox());

mmshow(b);

b

The opening top-hat procedure enhances the small objects relatively to its background. In the calculator image, the digits are enhanced.

c = mmopenth(a,mmsebox(5));

mmshow(c);

c

The threshold operator is used to separated the enhanced objects. This procedure is quite robust, since the background was reduced to very low levels with the opening top-hat.

d = mmthreshad(c, uint8(150));

Warning: upcasting image from scalar to uint8

mmshow(d);

d

In order to have just one object (i.e., connected component) inside each key, a dilation is applied.

e = mmdil(d, mmsebox(3));

mmshow(e);

e

The outside markers are built by taking the watershed (skiz) of the complement of internal markers image.

f = mmwatershed(mmneg(e));

mmshow(f);

f

The markers used are the union of the internal and external markers detected. They are displayed as overlay on the gradient image.

g = mmunion(e,f);

mmshow(b,g);

b,g

The calculator keys are extracted by applying the watershed operator on the gradient image, constrained by the markers detected.

h = mmcwatershed(b,g,mmsebox());

mmshow(h);

h

Superposition of the detected contours on the input image.

mmshow(a,h);

a,h