I am not sure I follow what you are doing. Does your mask look correct before you apply it (it shows 0s where you want to mask out values in an image)? If so, what is happening when you choose to Apply the mask? In the Apply Mask dialog, you can choose the value you want to give the masked areas (where there are 0s). You can't choose to apply values where there are 1's in the mask. Those will be left as their original values. Instead, you would have to make another mask where the 1s are the 0s in order to specify a new value for those areas in the Apply Mask. Perhaps you could let us know the steps you take to create and apply the mask. Or you could contact ITT Technical Support directly with this question.