Forum Login

A Digital Split Neutral Density Filter

By: Steve Kossack

A Photoshop Split ND Replacement


Gates of the Valley — Yosemite National Park 1999

I've been working digitally for several years now and I have never forgotten for a minute the reasons why. When I learned darkroom technique I was amazed at what could be done provided one had enough time and patience, not to mention skill. 

Now I find of interest any technique that will allow me to do digitally the basic darkroom procedures that I came to know and loved doing. The fact that these are done so much more quickly and especially with a degree of accuracy that was never possible in the dark is just "gravy" to me. We won't even mention not having to breath chemicals, though I am tempted sometimes to run a garden hose from the tailpipe of my automobile to my desktop for nostalgia's sake.

I have read with great interest the articles on this site on Gaussian Blur and Contrast Masking. These are great tools and I use them frequently, but I've always wondered how to easily duplicate the effect of a split neutral density filter. While these most useful of filters are a must for anyone doing landscape photography, occasionally they aren't available, or location logistics prevents their use.

Up until now I've used Layers in Photoshop to combine different exposures of the same scene. I shoot a separate exposure for the shadow, the mid-tones and the highlights. My success with these "composite" images has varied though. It's almost like being in the darkroom again. I look at the exposures and say to myself, "Well..., maybe given enough time I can rescue this."

Until recently it's been hard to find Photoshop articles and books just for us photographers. Prior to the recent explosion of digital cameras (from point-and-shoots to SLRs to high-end 3-shot backs) it was usually graphic artists and pre-press technicians using Photoshop, not photographers.

Recently though I've been reading Martin Evening's fine book titled Adobe Photoshop 6.0 for Photographers. Mr. Evening has a quick and simple solution for rescuing images that could have benefited from having a split neutral density filter applied.

Find yourself an exposure that has almost everything exposed properly save for the highlight or the shadow. In my example I've used one of my favorite images from Yosemite Valley. In the past I've always printed the under-exposed frame because I like the sky and reflection. This time I used the over-exposed one. It appears to have no sky detail, but dragging through it with the eyedropper tool in Photoshop and looking at the the Info Palette showed that there was information there!

Here's what to do:

  1. First, do everything needed for image correction as usual. For me this is cropping (in this case perspective cropping to level the horizon a touch) and Adjustment Layers for Curves and Selective Color.

  2. Make a new Adjustment Layer for Levels. Pull the gamma slider (center) to darken or lighten the image so that the highlight or shadow area is closer to how you want it to appear. This is where I first saw the color in my sky.

  3. With the Levels Adjustment Layer active add a Layer Mask using the icon at the bottom of the pallet.

  4. Make sure that you've chosen the default setting for foreground and background color (W/B)

  5. Now grab the Linear Gradient tool and drag in the image where you want the original to be revealed. In this image it was the bottom two-thirds.

Remember, the direction that you drag, and whether Black or White is on top of the Palette will determine the area affected. You also can change the part of the image that you drag over and how much of the total area is masked or revealed, and change the opacity of the masked Adjustment Layer itself.

Also feel free to experiment with using a brush instead of (or in addition to) the gradient tool. Keep in mind that the dark areas of the image are a mask! It can be erased in any way that you want and that's appropriate to the image.

This is just the jumping off point. Experimentation is what photography and Photoshop use in particular is all about. I hope that you find this technique useful.

Steve Kossack

All text and photographs on this page are Copyright © 1999 - 2001 by Steve Kossack

Filed Under:  

show page metadata

Concepts: Photography, GIMP, Digital photography, Image editing, Sun, Portable Network Graphics, RGB color model, Graphic design

Entities: Adobe, Palette, Yosemite Valley, Michael Reichmann, Mr. Evening, Steve Kossack, Photoshop, SLRs

Tags: image, adjustment layer, split neutral density filter, Photoshop, tool, gradient tool, basic darkroom procedures, new adjustment layer, Levels Adjustment Layer, high-end 3-shot backs, darkroom, Linear Gradient tool, color, darkroom technique, Photoshop articles, Contrast Masking, Adobe Photoshop, different exposures, garden hose, separate exposure, Gaussian Blur, breath chemicals, under-exposed frame, image correction, location logistics, Layer Mask, landscape photography, great tools, pre-press technicians, Martin Evening, simple solution, recent explosion, gamma slider, Info Palette, case perspective, eyedropper tool, Yosemite Valley, digital cameras, active add, graphic artists