Edge selection with Hard Mix

[dmstraker]

Here's a novel way of detecting edges and creating a simple outline layer.

Start with an image. Here's one taken in Kathmandu.

If you do a 'detect edges' on it (Filters/Detect/Detect Edges), it looks like this:

This can result in lots of little bits being selected too. What if you want to select less? One way is to use Levels or Threshold.

Another approach is to go via blending. Duplicate layer and set Blend Mode: Hard Mix. This simplifies the picture.

Now if you do a detect edges you get a simpler and slightly different set of lines.

The result is similar to Detect Edges, but with a harder edge selection effect.

Beyond this, you can Merge Down, Invert the layer, convert to b/w, do a Filters/Colours/Erase White Paper, play with Levels, Threshold, fx, Opacity, etc. Then you can use the line layer to darken, mask sharpening, etc.

You can also replace the Hard Mix with other contrast-increasing blends, such as Colour Burn and LInear Light. You can also force a hard contrast with Levels, squeezing the black and white points close together. Even cranking up the basic contrast forces edges to be more distinct.

Like many methods, it will work better on some images than others, and experimentation will help you figure out if and when you might use this.