Selecting Pixels by Brightness

Just ran into that time again when I want to preserve the shadows in a nicely backgrounded image. I usually end up saying, "screw it," and mask out the object and add in a fake background. Blah.

To select pixels based on their "brightness" (luminosity), ctrl-click the RGB channel.

To keep the shadows, invert the selection, and combine it with a masked layer of the object in question.

Frequency Separation

Using the high-pass method (vs. image-apply):

1. Create two duplicate layers ("texture" on top and "tone" next)
2. With regards to the texture layer
1. Apply a high-pass filter using a pixel radius to capture all fine details but not tonal or volume changes
2. Blending mode to Linear Light
3. Opacity to 50%
3. Gaussian blur the tone layer with the same pixel radius used for the high-pass filter

Freaky Amazing Details

I picked up this Photoshop sharpening technique from these sources:

https://www.youtube.com/watch?v=ZV9u0Wu8L0M
http://fstoppers.com/sharpening-with-blur-bring-back-insane-detail-with-this-quick-technique

And because no one on the web seems capable of putting together a simple step-by-step tutorial:

1. Make 2 copies of the original image (3 layers total)
2. Group the top two layers
3. Change the group's blending mode to Overlay
4. With regards to the group's top layer:
1. Blending mode to Vivid Light
2. Invert the layer
3. Apply a Surface Blur filter (better yet, change it to a smart object with the filter)

Seems like a radius=8 and threshold=10 is a good place to start for the layer.