An inversion, in noun form, is a reversal. In verb form, applying an inversion is inverting, or even “to invert.” In Photoshop, you can invert an entire image, or a single channel.
Inverting means reversing the color values that the adjustment is applied to. The effect this has depends upon the working color space, and tends to have the most dramatic and useful results in the LAB color space where the channels are based upon a color-opponent model.
The implications of a applying a Photoshop inversion adjustment are perhaps seen most easily in a monochromatic image. Notionally, all the information in the image is either black or white—all though this isn’t really the case, as I’ll get to in a moment. Therefore, when I invert the image black becomes white, and white becomes black.
For example, take this Dandelion etched in white on a black background:
Applying a monochromatic inversion gives me a Dandelion in grey tones on a white background:
Stepping back for a second, in modern digital practice monochrome—black and white—seldom really means dropping all the color information. (In a brief message from the sponsors of this blog, check out my book Creative Black & White: Digital Photography Tips & Techniques for a more thorough treatment of this issue.)
So if black isn’t black and white isn’t white, how can you expect to get the clarity of results shown in the Dandelion example? The simple answer is to convert the image to LAB, and only invert the Lightness (L) channel. This applies the adjustment only to monochromatic information and completely ignores color values. If you like what you get, consider dropping the other channels entirely!
Don’t forget to convert back to RGB or CMYK when you are done. LAB is a theoretical model, meaning it can’t be output in the real world.
Interested in digital black and white? Then my October 14-16, 2011 workshop at the Center for Photographic Art in Carmel, California may be for you. Here’s more information about the workshop, and a registration link.