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A
Simple Neutral Density Graduated Filter using Photoshop
- by Chris Maddock
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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;
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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.
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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;
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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' |
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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; |
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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.
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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. |
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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. |
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Now for
the "magic" bit. Draw a vertical line down over the area
that you want the gradient to cover; |
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When you
release the mouse, the adjusted Background layer will
appear through the Background Copy layer below the area
of the gradient; |
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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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