I have a irregular raster with empty spaces as seen in the attached image, which is the southwest corner of my raster. I would like to create a polygon or a mask that matches the non-white regions of the raster using QGIS.
When I went to "Vector -> Research Tools -> Extract Layer Extent," QGIS created the polygon seen in pink. Note that the left-most edge of the raster is in the image shown. In other words, somehow the layer extent goes beyond the visible part of the raster.
In any event, I would like to create a mask/polygon that covers only the visible part of the raster. In the image shown, it would mean a polygon that does not include the square empty space.