Man!... You just gota love the new Flood Fill feature of the MaskTool.
Especially if you want to do sky substitutions with beaucoup 'peek throughs'.
Granted the original here is almost ideal with an uniform background which almost never occurs in the natural world [but did in this case] but still the sky substition is made easier and more accurately with FloodFill than with a ColorRange or BrightnessCurve tone range background selection...
Original image and FloodFill Mask
sky1-2_ori_mask.jpg (31.22 KiB) Viewed 5954 times
Sky1 -- Gray Clouds
sky1.jpg (45.54 KiB) Viewed 5951 times
Sky2 -- Sunrise Clouds
sky2.jpg (47.53 KiB) Viewed 5952 times
The new editing features of PWP5 are outstanding and for me far outweigh any workflow/history preference issues.
I am perplexed. The flood tool generates mask for similar connected pixels. How can it generate mask for disconnected pixels, the multiple sections of sky completely surrounded by tree branches? The comment about the unusually flat background sounds like an ideal situation for the range tool. Is it possible that the range tool was used to make the mask in question?
The mask was constructed with the MaskTool -- Flood Fill where the threshold was set to 22.5 with multiple mouse clicks in the spaces between the limbs where there were 'peek throughs'... followed by a +1 Feather and -1 Feather to further soften the mask edges...
This proved to be far more exact, howbeit a bit tedious, in forming believable mask gradients between mask white and mask black than those achieveable with the ColorRange or BrightnessCurve [tone range] MaskTool features... at least for me.
The following is a 1:1 zoom at the original image resolution attempting to show the branches and composite blending 'peek throughs' detail of sky2: