Softening and Dramatizing a Butterfly
Original Image

Create a duplicate layer on top and desaturate that top layer.

Invert top layer colors.

Blur the top layer: Gaussian blur / pixels = 5% of image width

Set top layer mode to "Grain Extract" & set opacity as desired.
(Mouseover to see the original image.)
Using your favorite method, if desired, convert image to grayscale.

Experiment:
- Increase or decrease the contrast (using the "curves" tool) of the top layer before you blur it.
- Change the radius of the Gaussian Blur. Increasing the blur radius actually decreases the strength of the dramatizing effect.
- See variations of this method here: Chiaroscuro Effects
Some examples (mouseover to see the original image).