Hi, This is getting frustrating. I have a few cloud cover on my Landsat 8 image that I want to get rid of. So from the ROI Toolbox, I created a cloud ROI then saved it. Next I wanted to mask the clouds out of the image, so I went to Toolbox -> Raster Management -> Masking -> Build Mask. In the "build mask input file" window, I chose the image with clouds as input file, then clicked OK. In the "Mask definition" window, I clicked "options" and imported the cloud ROI I created previously. Then assigned a mask output name. Once the cloud mask was created, I then went to Toolbox -> Raster Management -> Masking -> Apply Mask In the "Apply mask input file" window, I chose the image with clouds as input file, then clicked OK. In the "select mask band" button, I put the cloud mask band I created. Then OK. Finally, in the "apply mask parameters", mask value = 0, then set the output name.. Then OK. Here comes the problem. After the process was done, the result was not the one I expected. I was hoping to have an output with a new image WITHOUT clouds. However, the resulting image is the cloud mask itself! Did I do something wrong? "Image with clouds" minus "clouds" = "image without clouds" ---- this is what I want. "Image with clouds" minus "clouds" = "clouds" ---- this is NOT what I want. Can anyone shed a light on this? I have done this process three times and the same result every time. Thanks for the help.