Usage of Step Function in Matlab Coder?

An excerpt of my code shown below:

%  Creating the detector for the face 
detector = vision.CascadeObjectDetector; 

%  Bounding Box for face
A = step(detector,I);

This basically doesn't work in the MATLAB coder as it says that A is undefined. The exact error is below:

"Undefined function or variable 'A'. The first assignment to a local variable determines its class."

If I use zeros and preallocate A, step just redefines it. Has anyone gotten around this?

Hope someone can help me on this one!

[Denis Gurchenkov]

I did the following:

- Saved this test into test.m:

function A = test
I = 1;
detector = vision.CascadeObjectDetector; 
A = step(detector,I); 
end

- Typed this in MATLAB propmpt:

codegen test

It successfully compiled and produced test_mex in bot 2014b and 2014a releases. Can you show what did you do to get the error? Which release of MATLAB you are using?

[Sharan Duggirala]

I seem to be getting these errors. Thank you for your help!

Answer 1

[Denis Gurchenkov]

Replace the assert statements with the following:

assert(isa(I, 'uint8'));
assert(size(I, 1) < 100);
assert(size(I, 2) < 100);
assert(size(I, 3) == 3);

This will make your example compile fine.

The catch here is that CascadeObjectDetector requires the input's 3rd dimension to be exactly 3. That is, the input must be NxMx3 array. Therefore the assert that size(I,3) == 3 is required.

Also, for code generation, CascadeObjectDetector requires the size of the input to be bounded. There fore the asserts for size(I,1) < 100 and size(I,2) < 100 are required. Of course you can change 100 to some other number, it just has to be some concrete number.

Does this make sense?

Denis.

function [rect] = bound(I)
  assert(isa(I, 'uint8'));
  assert(size(I, 1) < 100);
  assert(size(I, 2) < 100);
  assert(size(I, 3) == 3);
  detector = vision.CascadeObjectDetector;
  A = step(detector, I);
  rect = zeros(1,4);
  rect = [A(1,1), A(1,2), A(1,3), A(1,4)];
end

Answer 2

[Jonas Kandume]

How to code step function in matlab version 2020b?