How to create a marker for watershed algorithm?

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I like to create a marker for watershed based segmentation. Input is a GrayScale Image. If the intensity is in range 200 -225 then it is background else if the range is 100-199 then it is object. 0-99 May be object or background.

I read that the marker must be same size of original image and it must have int32 type.

1. which datatype the marker should be CV_8UC1 or anything else?
2. How can i define foreground,background and other object regions in marker.

Thanks in advance.