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A Simple Neutral Density Graduated Filter using Photoshop - by Chris Maddock

Undoubtedly we've all been in the situation where the difference in brightness between elements of a scene exceeds the capabilities of the capture medium. For example this shot of Derwent Water has a fairly bright sky but to retain any detail at all in the clouds would have resulted in the ground being underexposed.

The traditional way of dealing with this situation is to use a Graduated Neutral Density filter to hold back the exposure on the sky and balance it better with that of the ground. This, of course is what I should have done - had I taken my filters with me that day.
All is not lost for the digital user, however, as we can merge two images to retain the sky detail and lift the ground brightness. The simplest method is to directly simulate an ND Grad filter in Photoshop.
The source images can be acquired in several ways;

 

 

1. Bracketing at the time, taking two shots at different exposures - one for the sky and one for the ground. This does require the use of a tripod and no moving elements in the scene.
2. Shooting in RAW format and converting the image twice with different exposure compensations - one for the sky and on for the ground.
3. Exposing for the sky and manipulating the image afterwards. If you don't have a tripod or the facility to work in RAW this could be the answer for you.

For the purpose of this tutorial I shall be using the third method.
With the image open, we first need to duplicate the layer. This can be done either from the Layer menu or from the Layers Palette menu. When offered a name for the layer just leave it as the default.

Note; If you have two shots (from either of the first two options above) then you can copy the darker one and paste it onto the lighter one, which will create a new layer.

The Layers Palette will now look like this;

Now turn off visibility of the "Background Copy" layer by clicking on the eye symbol to the left of it in the Palette and select the Background layer'
This allows you to edit the Background Layer so that the ground is as you would like. I have used Curves to pull up the exposure and boosted the saturation a touch here. I have completely ignored what this does to the sky since that will be from the Background Copy layer when we have finished;
Now go to the Layers palette and select the Background Copy layer, this will also turn on the layer's visibility and it will completely obscure what we have just done on the Background layer. Don't worry, it's still there, just hidden for now.

Now we apply a Layer Mask to the Background Copy layer - in the Layers Palette, drag the layer down and drop it onto the Add Layer mask button.

This applies the Layer Mask, indicated by a white box appearing next to the background Copy layer in the Layers palette. The Mask box is surrounded by a thin frame, indicating that it is selected.

Now it's time to apply the simulated ND Grad filter. Firstly, go to the Toolbox and select the Gradient Tool. It may be hiding under the Paint Bucket Tool, if so click and hold on the Paint Bucket and a menu will pop out offering the Gradient tool.
Also, ensure that the Foreground Colour is set to white, with the Background Colour to black - because we are working on a Layer Mask they can only be black and white, but make sure that it's the Foreground which is white.
 
Now for the "magic" bit. Draw a vertical line down over the area that you want the gradient to cover;
 
When you release the mouse, the adjusted Background layer will appear through the Background Copy layer below the area of the gradient;
If you're not happy with the position of the gradient or the length of the transition area, simply redraw it as many times as you need until it is as you want. If the transition you want is not horizontal, then you can angle the gradient - just like positioning a real ND Grad filter at an angle on your lens.

If you now feel that more adjustment is needed on either layer, select the one you want by clicking on its thumbnail in the Layers Palette before editing it. The other layer will be unaffected except in the area of the Gradient transition. Finally, flatten the layers by choosing Layer->Flatten Image from the menu and you're done.
I darkened the sky a touch and tweaked the brightness/contrast of the ground to finish up with my final image - not necessarily a competition winner, but still a considerable improvement on the original so I framed it anyway.


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All text and photos are copyright © Chris Maddock, 2007