Note: This excerpt is from the forthcoming book The Hidden Power of Photoshop Blend Modes, ISBN 9780321823762.
Photographic Adjustments: Remove Vignetting
While I normally advocate using Camera Raw to remove vignettes, the following method is a pretty handy way to realize some basic recovery using the Divide blend mode. It also leaves you some creative latitude for additional effects, but it does have some limitations.
Use the Eyedropper tool (I) to sample the dark corners of your image. I recommend using a larger sampling area, so set your range to an 11 x 11 sample in the Tool options. You want to sample the general color and darkness rather than a point sample. Clicking in the corner will load your foreground with that color.
Press X to swap the foreground and background colors, and then click in the central, brightest area of your image to identify the foundation colors you’ll need.
Create a blank layer above your background, and choose the Gradient tool (G) with a radial gradient, using the Foreground to Background gradient in the upper left. (Click the Gradient sample drop down menu on the Options bar.) The bright foreground color should be in the center, and the background color should be at the outside of the gradient.
On the blank layer, drag from the center of the canvas out to the corner. You should have a smooth gradient extended from the middle. Then, set the gradient layer blend mode to Divide. The effect will be immediate, if a bit harsh.
Lower the opacity of the Divide layer, and use Blend If to recover some of the highlight detail. In the sample image, Blend If was applied to the gradient layer, moving the white sliders on This Layer from right to left, and splitting them quite a bit to soften the transition.
This technique can be faster than Camera Raw on some simple images, and allows you to change the center of the vignette correction much more easily. Plus, you have the added ability to adjust the colors or add a refinement mask, abilities that Camera Raw does not offer.
Unfortunately, this technique doesn’t work so efficiently with complex images or images with dark centers. You’ll have to mask those manually. On the other hand, this is a great way to remove backgrounds that are flat but unevenly lit.
Bonus! If you are able to first shoot a ”flat field” image with no subject, you’ll have the source for your Divide blend mode layer. Simply replace the gradient with your subject-free background.
- Use the Eyedropper tool to select the bright middle area as the foreground, and a dark corner as the background.
- Create a radial gradient on a blank layer above the background layer.
- Set the gradient layer’s blend mode to Divide.
- Lower opacity, apply a mask, and use Blend If as needed to control the effect.