Using the Sabattier Effect in Digital Photography

Although developed areas of the print are desensitized to light, partially undeveloped areas are still capable of being fogged.
If these are then allowed to develop normally, they will darken.
As the doctor and scientist who discovered this effect, Frenchman Armand Sabattier (1834-1910), described this process as "pseudo-solarization", it has become incorrectly known as "solarization" -which is, in fact, the reversal of image tones due to extreme overexposure.
Digital advantages For the traditional darkroom worker, the Sabattier effect is notoriously time-consuming and difficult to control - it is all too easy to spend an entire morning making a dozen or more prints, none of which looks remotely like the one you might be trying to copy.
Using digital image-manipulation techniques, however, this type of uncertainty is a thing of the past.
The first step is to make a copy of your original image to work on and convert that file to a greyscale.
Choose an image that has fairly simple outlines and bold shapes -images with fine or intricate details are not really suitable as the tone reversal tends to confuse their appearance.
You can also work with a desaturated colour image if you wish.
There are several digital techniques that allow you to simulate the Sabattier effect.
One way of proceeding, if you have software that offers Layers and Modes, is to duplicate the lower, original layer into a second layer.
You then apply the Exclusion Layer mode, and adjust the tone of the image by altering the Curves or Levels for either layer.
The most controllable and powerful way of working is to invoke the Curves control and draw a valley-shaped curve, with a more-or-less pronounced hollow in the middle.
By introducing small irregularities in the curve's shape you create surprising tonal changes - thus putting back into the process some of the unpredictability and charm of the original darkroom technique.
The advantage of working with Curves is that you can save them and then apply them to any other image you wish.
The Sabattier effect will also work with colour images but, as with the tones, the colours become reversed as well.
If you wish to avoid the hues becoming reversed, change the image to Lab mode, and then apply the "Sabattier" curve only to the L channel.