How can I automatically create a mask of the in-focus areas in an image?

Question

I need a way to isolate or mask only the sharp, in-focus parts of a photo for a research project. Photoshop CC is adding a feature for this, but are there other software options or workflows that can do it automatically or semi-automatically?

user24174 · Answer

I normally use GIMP for that --- this probably needs to be refined for automatic procedures. My procedure is as follow:

I load the image, in this case http://rlog.rgtti.com/wp-content/uploads/2013/01/10/macro-lenses-are-expensive-all-of-them/paseo_15sep_more_rosse.jpg
Now I copy the background layer, and I transform the new layer to grayscale.
I apply edge-detect by difference of gaussian:

enter image description here

playing with the parameters to have a nice area defined. Apply the filter

Now you apply a threshold to the image:

enter image description here

...and this is a map of your sharp (how much sharp you decide in the previous step setting the parameters for the filters) are.

You can now use the "select by color tools", click on the black, and then grow the selection a bit:

enter image description here

... once you are satisfied, you can save the selection to a channel.

Notice that the selection do not include the sharp areas which are uniformly colored, without edges. I do not know any way of doing this automatically (is it possible?); but you can copy the channel to a new layer and

manually edit the layer to fill the sharp areas with black:

enter image description here

...and the repeat the select-by-color procedure to create a new mask.

How can I automatically create a mask of the in-focus areas in an image?

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