Graduated Neutral Density Filter
Graduated Neutral Density (GND) filters are popular photographic tools that enable you to balance scenes with wide dynamic range. These glass filters attach to the front of a camera lens, and photographers typically use them for landscapes, sunsets, sunrises, and other scenes where the sky is far brighter than the land. A basic ND filter behaves effectively like sunglasses for your camera, reducing all incoming light (hopefully in equal amounts across the spectrum). A Graduated ND filter has a density ramp (a gradient) from clear to dark, allowing you to more easily balance exposure in a single frame by aligning the clear-to-dark transition with the appropriate areas of your scene. You can create GND filters in Photoshop to help balance your images in the same way. In addition, you can use them to create vignettes and other artistic looks. Just don’t expect miracles: The following GND methods can’t recover detail that is already lost in your original image, either by shadows that are too dark or highlights that are blown out.
The traditional digital approach for a sunset photo is pretty simple, assuming the sky is a bit too bright for the foreground. Create a blank layer, name it GND, press D to set the default foreground and background colors to black and white, and then grab the Gradient Tool (G). From the options bar, choose a linear gradient, and then drag from top to bottom while holding the Shift key. The Shift modifier ensures the gradient is dragged perfectly in the vertical (or horizontal or at 45 degrees, depending the direction you drag). Your result should be black at the top and white at the bottom.
Change the blending mode of the GND layer to Multiply to start. Notice the black areas bring down highlights, while the white areas of the gradient don’t have any effect on the image. Lower the Opacity of the GND layer until the values are more balanced. Unfortunately, I find that many images suffer from loss of saturation, and the result is something a little too muted for my taste.
Instead, I like to experiment with Color Burn and Overlay, depending on the dynamics and what I want out of the process. Color Burn can be really, really harsh, but fortunately it responds differently to Fill than it does to Opacity. For this particular image, lowering the Fill setting of the GND layer to about 55% gives a great result for the sky in this example.
In some situations, it may be better to actually duplicate the photo layer rather than applying a gradient. Duplicate the photo, and change the copy’s blending mode to Multiply. Use the Gradient tool to add a layer mask to the copy, and this time let the sky show through while masking the foreground. Keep in mind that while a mask is selected, pressing D will load white to the foreground and black to the background, but also swaps the gradient colors if you’re using Foreground To Background as a preset.
Both methods allow for all kinds of customization and tinkering. Duplicating the photo layer and using Multiply quickly burns the image overall, so be sure to keep an eye on artifacts in the darker areas. But any color regions will immediately start to pop. Similarly, Overlay will burn dark areas while dodging light areas—something to keep in mind if you are dealing with a low-contrast image, such as on a hazy, gray afternoon.
The next step in building on GNDs is to expand the idea to vignettes. While the technique is very similar, the intent is quite different. A GND is meant to manage dynamic range; vignettes are primarily meant to guide the viewer’s eye around the photograph.