Life is like that, too. Here the mask is the black shape that cuts out the gold from a previous document. In a case where the two are not necessarily touching one could use two masks, one to cut out the gold and another to cut out the silver background. It seems cumbersome, but those 3 steps can yield extremely complex and ultra clean pictures and it is still light years faster than any manual touch up, or trying to rope in the parts via selections and then pasting. Before and after the Gaussian Blur filter What we need to accomplish with this is to add more transitional grayshades to the mask, so that where it used to jump from black to white, it now steps through dozens of shades.
Life is like that, too.
You can blow it up at will or shrink it . The range here is determined by the initial amount of Gaussian Blur. I tried to change over just to synchronize on the names and to lessen the possible confusion factor I may introduce to others, but with best intentions I find myself time and time again gravitating back to black shapes for my masks. It is ultimately of no technical consequence and does not affect the process or quality one bit one way or the other, but many people before me have tripped over this and I felt it necessary to state it once. There is lots more still, both about masks and compositing, as well as Channel Operations.