Issues with a thresholding function

I have the following function:

function rgbMap = thresholdFunction(x)
rArray=zeros(size(numel(x)));
gArray=zeros(size(numel(x)));
bArray=zeros(size(numel(x)));

rArray(x>110 & x<=152) = 255;
gArray(x<=110) = 255;
bArray(x>152) = 255;

rgbMap = cat(3,rArray,gArray,bArray);

end

Which then gives the error message: 'Dimensions being concatenated are not consistent'

The function is designed to apply thresholds to a grayscale image which is the input 'x', and give a colormap of the different value selections 'rgbMap'.

The reason I'm using a function instead of applying the thresholds directly to the image, is because it's part of a batch processing code, and so 'x' would end up being more than one image being put through a 'for' loop.

I am fairly new to Matlab so if I'm doing something ridiculously stupid, feel free to point it out!

Answer 1

[Geoff Hayes]

Andrew - look at the line

 rArray=zeros(size(numel(x)));

numel returns the number of elements in x so this could be (for example) 42 which is a 1x1 scalar. Finding the size of this scalar will be

 >> size(42) 
 ans =
     1     1

and so all of your arrays will be 1x1. Just remove the numel from each of your array initializations so that the arrays are of the same dimension/size as the two-dimensional x.

Note that the error is occurring because while each of your arrays begin as 1x1 arrays, their updates with

 rArray(x>110 & x<=152) = 255;
 % etc.

will not guarantee that each of the three has the same dimension (even if they did, this is not the answer you want) and so you end up trying to concatenate three matrices of different dimensions.

[Andrew McLean]

Knew it would be something like that, thanks for the answer