Unexpected error with imfill

I am attempting to use imfill to floodfill a donut shaped binary matrix. I am using version R2018b. I want to fill the donut (not the central hole) by sepecifying a pixel coordinate within the "dough". I am trying to run this command:

testFill = imfill(testShape, [3 3], 4)

As reccomended by the documentation:

BW2 = imfill(BW1,[3 3],8)

However, I get this error:

Error using imfill>parse_inputs (line 248)

Expected input number 3, OPTION, to match one of these values:

'holes'

The input did not match any of the valid values.

Error in imfill (line 124)

[I,locations,conn,do_fillholes] = parse_inputs(args{:});

Caused by:

Error using validatestring>checkString (line 89)

Expected input to be one of these types:

char, string

Instead its type was double.

Answer 1

[Walter Roberson]

That particular syntax is only valid if your input array is type logical, but your BW1 is some other data type. For example, it would not be enough for the array to be double(0) and double(1), or uint8(0) and uint8(1), or uint8(0) and uint8(255) : it must be logical.