A Simple Colour Graduated
Filter using Photoshop
by Chris Maddock
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Following on from my Neutral Density
Graduated filter article, this uses
the same technique to apply a graduated
colour filter.
Here
I have an image that I shot at Bedruthan
Steps where Murphy's Law prevailed
and the sun disappeared behind a cloud
bank before giving me any colour in
the sky. I'm going to use this as
the example and add a simulated warmup
grad filter.
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Now, I only want to warm up the
sky (and a little of the distant
sea) but a grad filter will give
a horizontal transition across
the whole image - including the
rocks, which I don't want.
So
the first thing I need to do is
to select the area which I want
to exclude. The quick and dirty
way to do this is to use the Magic
Wand. As it happened, with a tolerance
of 32 one click selected all I
wanted, so I don't need to alter
the selection at all.
Further
detailed adjustements to the selection
can be made but this is outside
the scope of this article.
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I now save this selection for use
later, by choosing Select->Save
Selection. I left the destination
as the current file and the Channel
as New, just entered something in
the Name - I've used "rocks"
Finally,
I clear the selection, using Select->Deselect
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Now I duplicate the layer (Layer->Duplicate)
and leave it as the offered name,
before adding a new layer (Layer->New->Layer).
I
haven't renamed this layer but I
have altered the trancparency to
25%, the reason for which will become
clear later.
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A quick glance in the Layers Palette
shows that I now have three layers
- the original "Background"
image, a duplicate "Background
Copy" and the new "Layer
1"
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I
now add some colour to Layer 1,
to start creating the simulated
filter. First I click on the colour
picker foreground colour and type
in the colours I require. In this
case I am simulating a Wratten 85
warmup filter so I use R 228, G
137, B 0.
Other
values for different filters are
given at the end of the article.
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Having
selected the colour, I now use the
Floodfill tool to apply it to the
whole of Layer 1
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I now combine the layers Layer 1 and
Background copy so that the whole
of Background Copy is warmed up. This
is done in the Layers Palette by clicking
on the arrow at the head of the tab
to open the menu and choosing "Merge
Down".
This
merges just the selected layer and
the layer below it in the list, leaving
us with two layers - the original
image "Background" and the
warmed-up duplicate "Background
Copy".
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Now,
as with the ND Grad article, I add
a Layer Mask to the "Background
Copy" layer.
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Now
I apply the gradient to the masked
"Background Copy" layer.
I set the colour picker foreground
colour to White, select the Gradient
Fill tool and draw a vertical line
on the area that I want the graduation
to cover.
Voila!
one gradient warm-up filter
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However, if you look closely at the
previous image you'll see that the
gradient has also covered the rocks.
Not what I wanted.
Never
mind, I'd already planned for that
- remember the selection I created
and saved?
I
now load that selection onto the Layer
Mask that included the gradient fill,
by going to Select->Load Selection,
pulling down the Channel list and
choosing the entry "rocks".
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Once
the selection is loaded, I can use
it to add that area to the Layer Mask
so that the grad fill doesn't cover
the rocks.
I
switch the Colour Picker foreground
to Black (to add to the mask), select
the Floodfill tool and click inside
the selection.
Now
the rocks have been excluded from
the grad fill.
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Having removed the selection (Select->Deselect)
I now want to adjust the amout of
the warm-up as it's a bit more than
I wanted.
In
the Layers Palette I select the Background
Layer by clicking on its thumbnail
- the image thumbnail, not the mask
- before adjusting tthe Opacity slider.
76% is about right so I'll leave it
there.
I'm
now happy with the result so I flatten
the image (Layer->Flatten Image)
and it's ready for finishing off.
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The RGB values I used above were for
a Wratten 85 and are those used in
Photoshop CS's Photo Filter tool.
Other filter values that CS offers
are as follows and can be used in
the same way when setting the colour
of the filter in this technique;
#85: R=228 G=137 B=000
#81: R=235 G=177 B=019
#80: R=000 G=066 B=255
#82: R=000 G=158 B=255
All of the above have an indicated
density (transparency) of 25%.
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