@John Kau: Please post as an answer, that you've solved the problem by restarting the computer and accept it. Of course we believe, that you are convinced, that you have not changed anything. But without any doubt restarting the computer removed the problem, e.g. by saving a changed M-file. So you did change something, even if you are not aware of what it was. Computers are not magic!
I've never heard of BMP format being able to store floating point values. I only hear of integer values. Where inhttps://en.wikipedia.org/wiki/BMP_file_format do you see that it can take floating point values? If you want to store floating point values, you can save it with save() in a .mat file.
You did not initialize "i", so it will have its default value as being sqrt(-1), the imaginary unit. You cannot index a cell array at an imaginary unit.
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