Hello, First of all, sorry if the question is stupid, but I am still a beginner in remote sensig, I work with ENVI 5.1 on Landsat 8 images. I want to apply cloud masks on a same image ( a NDVI created from landsat 8 bands ). I created the cloud masks from the QA band of Landsat 8, the first cloud mask is a classic one, made for masking the clouds of the image, the second one correspond to the opposite of the cloud mask of another image, the purpose here is to retrieve the pixels that are without clouds and that corresponds to the pixels hidden by clouds on another date. When I apply the first mask, there is no problem, but when I apply the second one ( the opposite mask ), there is a difference between the result and the mask, as if the cloud mask had a translation of 200meters to the west. When I try with other images there is the same result. I think maybe it could be a problem with the projection, since there is something seeming strange to me. Indeed, while my landsat images are in UTM zone 49 North, whenever I produce something with those images ( a mask, or a masked image ), the result has a projection of UTM 49 South. However, if I try to reproject my results in UTM 49 N, using Qgis, it doesn't gives me a small change, but rather a big difference of hundreds of kilometers to the north. Furthermore, I don't see why I would have this difference when I apply the mask while the NDVI image and the two masks are all in UTM 49 S and seem to correspond. Although, maybe there is a problem with the dimensions ? Indeed, what seems also strange is that my images have dimensions of 7621*7771, while my other landsat 8 images located on the same area are in 7631*7771, so I cannot use them together. If you would have any lead ( for that matter or for changing the dimensions ), I would be very grateful :)Have a good day,