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Lesson Of The Month Correcting Perspective With Architectural Shots
By Ben Clay/Web Photo School May, 2003
Lesson Of The Month
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Photos © 2002, Ben Clay, All Rights Reserved
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One of the biggest challenges
in taking architectural photographs is being able to control the perspective
of the shot. Rendering an image so that the vertical lines of a building
are parallel to the crop of the image usually requires the photographer
to shoot with a view camera or Perspective Control (PC) lens.
Lacking that, it is possible to make adjustments for perspective after
you’ve already taken the shot with your camera. This lesson illustrates
some simple perspective techniques using an Olympus E-20N digital camera
and Adobe Photoshop.
On a recent trip to Las Vegas for a photo trade show, I happened to
be staying in a hotel room that looked out at the back of the Paris
hotel. As with most hotels and casinos in Vegas, the Paris is spectacularly
illuminated at night. From my hotel window, the building seemed to glow
from within and since I had my gear with me, I decided to photograph
it.
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I set my Olympus E-20N digital
camera on a tripod, opened the balcony window and framed up a horizontal
shot through the viewfinder. I guessed that the outside lights were probably
high pressure sodium vapor flood lights (which run somewhere between 1900-2100ÞKelvin),
so I set the White Balance to the closest preset (Tungsten, 3000ÞK)
and figured I could adjust the color shift later in Photoshop. (For a
closer look at how White Balance works, check out the lesson entitled,
“Using Digital White Balance Outdoors” in the Digital section
of www.webphotoschool.com.)
I set the aperture to f/5.6 and took several shots at various shutter
speeds until I arrived at a good exposure. This last shot was captured
at 1 second. To prevent any camera shake from such a slow shutter speed,
I used an Olympus Remote Cable to trigger the shutter.
Since I had my laptop with me, I decided to view the result on a larger
screen. I removed the Olympus SmartMedia card from the camera and uploaded
the images to the laptop via an Olympus SmartMedia card reader. Once the
images were written to the hard drive, I opened up the last shot I took
in Photoshop (#1).
While the exposure of the image was good, I noticed a couple of things
I wanted to “fix” digitally. I noticed that the color was
considerably different, but I decided to fix that last. Instead, I went
to work on fixing the angled perspective of the shot.
Had I been shooting with a view camera (4x5, 8x10), I would have been
able to adjust the front and rear standards of the camera to make the
vertical lines of the building parallel with the crop of the image. But
even though my digital SLR was incapable of performing such a feat, Photoshop
would allow me to modify the image to make it look like it was shot with
perspective control. Here are the digital steps to straighten out the
building and correct the color:
First, duplicate the image layer by pressing Command-J (PC: Control-J).
Next, select the bottom layer and press the D key to set the foreground
and background swatches to their default colors (black over white). Then
fill the bottom layer with white by pressing Command-Delete (PC: Control-Delete).
You will notice that the bottom layer is now pure white (#2).
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Next, give yourself some adjustment
room by expanding your canvas. Choose Image>Canvas Size…, increase
the canvas by 500 pixels in both the height and the width and press OK.
Next select the top layer and disable the positioning lock by clicking
on the Lock icon above the layer. This will allow you to move and distort
the top layer.
Next, you’re going to want to widen the top end of the image so
that the vertical lines of the building will ultimately be parallel to
the crop of the image. First, choose Edit>Transform>Perspective
to activate the sides and corners of the layer (#3).
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You may need to position a
couple of Guides to help you see when the lines are straight. To do this,
press Command-R (PC: Control-R) to produce Rulers on the top and left
sides of the image (if they aren’t already there). Then click inside
the ruler and drag a Guide out onto the image. You can drag as many Guides
onto, or off of, the image as you want. Just remember that after you’ve
released the mouse, you can only adjust the position of a Guide with the
Move tool.
Next, click either of the top
corners of the layer and drag it outward until the vertical lines of the
building line up with the Guides. You may need to slide the top center
point slightly to one side to have it line up perfectly (#4).
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Depending on the lens you’re
using or the position you happen to be in, you may notice a slight bubble
distortion in your photographs. In other words, it may look as though
your subject (building) was shot with a somewhat wide angle lens because
the lines of the building are somewhat bowed. In this particular case,
my position in relation to the building was pretty much fixed, as I couldn’t
move either forward or backward. Subsequently, I had shot this image at
the wide end of my zoom lens to capture the entire building, but at the
expense of distortion.
And yet, Photoshop once again
came to the rescue on this issue as well. To reverse the bowed effect
of a wide angle lens, select Filter>Distort>Pinch… to pull
up a preview window. To get an idea of how much pinching you need to apply,
minimize the preview window until the entire layer is visible. Then slide
the Amount until the preview looks straight. In this case, I applied 4
percent (#5).
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This subtle Pinch function
can really help to straighten the bowed sides of your image, but keep
in mind that it works best with an increased canvas size, like we have
here. Otherwise, your results may look contrived.
Once you have your perspective set, clear your Guides by choosing View>Clear
Guides and then choose the Crop tool from the Toolbox. Make a crop selection
by clicking and dragging diagonally across the image. You can adjust the
positioning of the crop by dragging the points in the sides of the selection.
To activate to crop, press Enter (#6).
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Finally, I wanted to adjust
the color of the image. There are many ways you can modify color in Photoshop,
and here’s a simple one. Since the yellow lights on the building
had a somewhat blue-green cast, I pulled up the Color Balance window (Mac:
Command-B, PC: Control-B), moved the top slider 30 points toward Red,
and the middle slider 30 points toward Magenta. By adding Red and Magenta
to an image, you automatically reduce the levels of Cyan and Green. This
quick adjustment made the greenish yellow a more warmer gold (#7).
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Sometimes when you create a
drastic shift in color, the colors may appear to be overly saturated.
To tone down the saturation, press Command-U (PC: Control-U) to pull up
the Hue/Saturation window, reduce the saturation by 15 points and press
OK (#8).
Finally, flatten the image by choosing Layer>Flatten. By flattening
the image, you will be able to save the image as a TIFF for printing or
as a JPEG for e-mailing or posting to a web site.
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If you plan to e-mail or post
your image to a web site, make sure to first re-size it appropriately
(600 pixels or less) and then apply a little sharpening to give the image
some crispness. For a more detailed look at how to prepare images for
print, e-mail, and web sites, check out the lesson entitled, “Preparing
Digital Images For E-mail And The Web,” located in the Digital section
of www.webphotoschool.com.
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Here we can see the improvements
we’ve made over the original image. The angles of the hotel are
straight, there is no wide angle lens distortion, and the colors are much
more true to life (#9 and #10).
Technical Information
Camera/Media: Olympus E-20N digital camera; Olympus RM-CB1
Remote Cable; Olympus USB dual slot media reader; Olympus 128MB SmartMedia
card; Manfrotto carbon-fiber tripod with a G1276 head; Apple iBook laptop
computer; Adobe Photoshop 7.0
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