I'm trying to find a really good, detailed description of how Select > Sky works. It has bitten me a couple times, especially when the first attempt using Select > Sky did not produce a complete selection of the sky and I then needed to use another tool to add to the selection. I've learned quite a bit through experimentation, but I'm wondering if someone has actually written about or made a video with useful material on this topic, specifically identifying the limitations of Select > Sky. What I am finding is that Select > Sky will work quite well in certain situations, particularly those where the sky is significantly different in color or brightness from the adjoining non-sky areas, in other words it is easy to find the edge between the sky and non-sky parts. In those cases the sky area appears white in the mask and the non-sky areas appear black. However, even when there is a well defined boundary, I also find that the "marching ants" are not a true indication of what has been selected. If I Alt + Click on the layer mask thumbnail I get a full screen monochrome view of the layer mask. In most cases some of the area outside the part marked as the selection by the "marching ants" is still partially selected as indicated by gray tones rather than being completely black. There is usually some visibility of the image in the non-sky areas near the bounday between sky and non-sky. You can see what I'm talking about in the image below where the Sky is completely slected but the eve and part of the roof of the old building are partially selected. When trying to add to a selection made with Select > Sky and using the Polygon Lasso Tool, the area added is 100% selected and may not match what was partially selected by Select > Sky. Any more specific information or explanations would be appreciated. Thanks in advance.