You know that neutral density graduated filters (ND grads) are widely used by landscape photographers to balance the different lighting levels between the bright sky and the darker foreground. For many subjects where there is a clear line between the two regions, a ND grad works well to balance the overall exposure.
There are times, however, when it is difficult to position the transition line of the filter. For example, in this shot taken on the Kirkstone Pass in the Lake District, the exposures required for the sky and the hillside are quite different and the transition from one to the other needs to follow the U-shaped valley edge. In the original shot the camera metering has been compromised so that neither area is correct.
One way around this is to take two identical shots exposed for the sky and valley but I came upon this scene by chance and didn’t have my tripod, so registering the two shots later in Photoshop would be difficult. Instead I decided to use this alternative approach taking the original Raw file and creating two copies from it with different exposures. These can then be overlaid and masked to provide a well-exposed result.
1 Do the conversions
Opening the Raw file in Photoshop automatically opens Adobe Camera Raw (ACR). Adjust the exposure by +0.5EV to bring out the foreground, click the Save button and save the file in Photoshop format. I called it Valley. Then repeat the conversion but adjust the exposure to -0.5EV for the sky. Click Open Image to save the file in Photoshop.
2 Arrange the images
Open the saved file adjusted for the foreground. Click Window>Arrange>Tile to display them side-by-side. Click on the image exposed for the sky. Rename the Background layer Sky by double-clicking on the layer. In the layer palette, click on the Background layer in the other image and drag and drop it onto the Sky image.
3 Adjust the layers
Rename the new layer Ground and close the original ground image. We now have a single image with two layers, Ground and Sky. If needed drag the Ground layer above the Sky layer. With the Ground layer selected add a layer mask by clicking Layer>Layer Mask>Reveal All.
4 Use a mask
Now mask out the Ground layer to reveal the Sky layer below. Click the mask icon to make it active. Select the Brush tool (B) with black as the foreground colour – hit D to give the default foreground/background colours. Using a large, soft-edged brush (I used 300px) paint over the sky area allowing the layer below to show through.
5 It’s time to paint
Paint over the sky area. Zoom in (Ctrl and +) and alter the brush size around tricky areas – ‘]‘ key increases size, and ‘[‘ reduces). The ‘\’ key toggles the visibility of the mask as a red overlay showing the areas affected. If you make a mistake, paint the mask back with white paint.
6 Final step: tweak contrast
Finally I decided to add a little additional contrast. I added a Curves adjustment layer and modified the curve into a gentle S-shaped bend by dragging the right side of the curve upwards, lightening the highlights and the left side slightly downwards to darken the shadows.
Taken from the May 2011 issue of Advanced Photographer magazine