Question
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?
Expert Answer
Neeta Dsouza
PhD Expert
Answered Aug 23, 2026
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.
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
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