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. |
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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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| 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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