How to Select>By Color but limit the affected area?

Something I’m interested in learning how to do is to replace the sky in photos. The reason for replacing the sky is that it is dull which equates to somewhat uniform colors. The Select>By Color tool works pretty good but when you get close to the sky’s edge it would be desirable to confine the affected area. For example, what about limiting Select>By Color to a specific area that could be defined by a path or even a Rectangle Selection on a small portion of the picture?

One option would be to use one selection tool such as select by color and then go to the lasso selection tool and use either the intersect or subtract from current selection to limit the affected area. See the user manual if you are unsure about how this option works.

As previous post, the selection tools have various modes, Default is usually Replace, you can make a initial rectangular selection then for Color select inside that selection use Intersect mode.
Example of that Using the “Draw Map” option adjusts the threshold value by dragging the mouse sideways.

You can adjust that selection but better to make a layer mask from the selection and tweak the mask.

Another way is use a luminosity plugin (there are several) to get the selection.

Good advice from rich2005.

I frequently use my luminosity mask plug-in to get a selection followed by a very loose selection with the free select tool in subtract mode to remove anything unwanted from outside the selection area. This usually provides a quick way of achieving the result.

For skies especially with twigs and stuff on the horizon, rather using Selection, I have found making a mask based on Color>Threshold more convenient.

First, I have to admit that Masks are something I do NOT know much about.

However, while aware of Intersect Mode it looks like I hadn’t appreciated how it works. Using the “Free Select” (Lasso) tool does allow defining an area as I had imagined. Then using Select>By Color in Intersect Mode has the affect I was seeking.

At least on the photo I’m presently working on the results are pretty good but I do think I need look into how masks work even if NOT the way to solve this problem.

Thanks to all respondents for helpful advise.

Masks are a very powerful means of selectively modifying parts of an image. They can be converted to selections and vice-versa.

The suggestion from xpatUSA is one way of creating a luminosity mask.

I read the original post by Pat David on luminosity masking and used the plug-in, coded by Saul Goode, for many years until it was broken by an upgrade. I then decided to create my own plug-in. I wished to have masked layers (or zones) of brightness which were independent, other than a small overlap at the boundaries to assist blending between adjacent zones.

After many iterations, my current version creates five independent masked layers and I have an analogue for saturation with three layer for high, medium and low saturation. These are used on a daily basis.

However, they require Python 2.7xx. I am sure we must have a resident genius who can convert them to Scheme, or even write a program for automatic conversion of Python plug-ins!


How do you know that’s not the way if you don’t know about mask?

For instance, 10 seconds using a channel to separate the blue and green from the sea and vegetation to the blue from the sky and put it as a mask via the channels… and no selection at all.