I'm trying to find a really good, detailed description of how Select > Sky works

[Bill Junk]

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.

[Myra Ferguson]

Select Sky is similar to Replace Sky in that it creates a selection that you can modify. If you take a look at Replace Sky (Edit > Sky Replacement...), you'll see that the mask it creates gives you flexibility for adjusting the color and the brightness of the sky that would affect the surrounding landscape in the rest of the image.

If you want a selection of the sky that is more crisp, you can create a layer mask from that selection and adjust its levels.

[davescm]

The marching ants represent the 50% point not the 0% or 100% edge. It is normal to have some slight feathering on the edge of a mask, without it the edge looks false.

many automated masking tools provide a good starting point but that is all.

Once you have a basic mask, you can refine it with brushes or adjustments as required. As an example, to sharpen up a mask in local areas, set a brush to overlay brush blending mode and paint on the mask with black or white  - black will darken the gray edges, white will lighten the near white edges. You can soften areas of the mask with the blur tool.

Dave

[Bill Junk]

Thank you for that update.  Since I posted this message I did figure out that the marching ants aren't representing the outter boundary of the selection.  It is nice to know that it's really a 50% point.  It took some time just experimenting, but I now have learned a lot about manipulating selection masks and feel relatively comfortable in adjusting them.  Seems like every time I learn something new in Photoshop, it opens up a whole bunch of other stuff that I then need to learn about.

    Bill

[davescm]

We never stop learning 🙂

Dave