The effect is most likely mainly local contrast enhancement, not just regular global contrast. That’s why it makes edges, textures, and terrain detail stand out without behaving like a simple contrast slider. A bit of additional sharpening may also be part of it.

To approximate it:

• Use a local contrast or clarity/structure style adjustment.
• If needed, add a small amount of sharpening afterward.

From the answers provided, darktable’s Local Contrast module gives a similar result and is a good open-source starting point. In general, look for tools labeled:

• local contrast
• clarity
• structure
• midtone contrast
• sharpening

So if you’re implementing it, think in terms of boosting contrast over small spatial areas rather than changing overall image contrast across the whole frame.