doc imread
Read image from graphics file
Syntax
A = imread(filename)
A = imread(filename,fmt)
A = imread(___,idx)
A = imread(___,Name,Value)
...
Description
A = imread(filename) reads the image from the file specified by filename, inferring the format of the file
from its contents. If filename is a multi-image file, then imread reads the first image in the file.
A = imread(filename,fmt) additionally specifies the format of the file with the standard file extension indicated
by fmt. If imread cannot find a file with the name specified by filename, it looks for a file named filename.fmt.
...
A = imread(___,Name,Value) specifies format-specific options using one or more name-value pair arguments,
in addition to any of the input arguments in the previous syntaxes.
...
Ergo, the first argument must be a valid filename string; you've passed what looks to be an array, I.
