Converting Image data from integer to double

Hello

I have a question concerning image transformation from uint8 to double.

I want to do an image band rationing (NDVI) and I need to transform my image band data from integer to double, so their ratio result in double precision.

The problem occurs when I am trying either to transform an image band to double ---> using cast()

The resulting in image is a binary image !

The same thing happens when I am transforming all the image to double using cast() (not only an image band).

Do you know what is the problem ? Is there any other way to do an image rationing ?

Thank you in advance

Greetings from Greece