function checkImage​AndNetwork​ChannelSiz​es

I'm using MATLAB R2019b and I'm trying to create a CNN model that takes grayscale images as input. However, I got the error in checkImageAndNetworkChannelSizes function even though both image channel size and network channel size are 1 because ndims(I) of grayscale image is 2 and therefore the first part of the conditional statement is true. Is this a bug? Is there a way to get around this? I try to add singleton dimension to my image but it seems to be ignored/dropped.

function checkImageAndNetworkChannelSizes(I, networkChannelSize)

% If the input image size has a different channel size than that of

% the network input size, we need to error.

[~, ~, Isize] = size(I);

if ndims(I) ~= 3 || Isize ~= networkChannelSize

error(message('vision:rcnn:invalidInputImageChannelSize', Isize, networkChannelSize));

end

Answer 1

[Jyothis Gireesh]

Here are a few pointers which may be of help:

• The function “ndims()” ignores all the trailing singleton dimensions of the input matrix. Hence it ignores the third singleton dimension and returns 2 when the input is a 2-D matrix.
• One possible workaround is to use the “permute()” function as follows:

if ndims(permute(I, [3 1 2])) ~= 3 || Isize ~= networkChannelSize 
    error(message('vision:rcnn:invalidInputImageChannelSize', Isize, networkChannelSize)); 
end  

If “I" is of size m x n, the permute operation changes the size of the matrix to 1 x m x n and “ndims()” returns 3.

This method may create an error if “I” is a 4-D or higher dimensional matrix.

• Else you may include another “if” condition which checks whether “ndims(I)” is equal to 2 or not.

Hope this helps!!

[Nicha]

Those are great answers! May I ask how and if I can change this internal function? MATLAB didn't allow me to change and save it when I tried.

[Jyothis Gireesh]

It is not a recommended pratice to edit the contents of a MATLAB internal function.

The problem may be due to wrong arguments provided in the "imageInputLayer" or any other layers of the model. Could you attach the code so that I can take a look at it?