I’d like to introduce to you one of the features of Photoshop some of you may not be familiar with simply because these are the kinds of features found on large format view cameras. You know, those old wooden (not so old, they still make them) cameras with big accordion type bellows and a person hiding underneath a black cloth to keep the light out while looking through the camera’s lens. Working with a view camera might be painful and hard to learn, but this exercise is not.
If you’ve ever wondered how to straighten leaning buildings so they look like they were shot with a view camera, here’s a tool for you. It even works for product shots!
The Photoshop Lens Correction Filter – Basic Exercise
Please note: I won’t be discussing all the features of this filter because it dilutes the purpose of simplifying the process. If you would like to know more about this filter, check out the Photoshop Users website for complete tutorials on the Lens Correction filter.
For this first step of the exercise, download the photo Quadrilateral.jpg and open it in Photoshop CS3 or CS4 (earlier versions do not have this feature, sorry). We’re going to take a look at how to compensate for the perspective distortion that happens when looking up and/or down at an object. Let’s explore how this works.
Perspective Correction Exercise 1
In order for a camera to see any rectangular (or square) shaped object as perfectly square (in this case, meaning 90º angles at all 4 corners), the camera would have to be dead center to the subject. In this perspective correction demo, the “camera” is slightly above and to the right of our subject, causing it to appear as a quadrilateral (that’s a rectangle where all corners have different angles)
Let’s do it.
1. Open file Quadrilateral.jpg in Photoshop
2. Go to Filter/Distort/Lens Correction…
Hey, here’s where the Lens Correction… filter is located.
For this exercise we will only be using the Transform portion of this dialog box.
Lens Correction Dialog before corrections are made
3. Using the Grid as a guide, start adjusting the Vertical perspective by dragging the slider until you have a parallel left and right side. A good number to obtain “square” on this correction would be +40
4. Now adjust the Horizontal perspective by dragging the slider until you have a parallel top and bottom line. Over and under correcting will render additional distortion. A good number to obtain “square” on this correction would be -30
5. Don’t touch that Angle dial! If you need to straighten your image, I suggest using the Ruler Tool to straighten things up before you start or after you’re done (a quickie tutorial coming soon) with your lens correction.
6. Look down to the next part of the Transform dialog – Edge. There are three choices:
a. Transparency – is just that, Photoshop leaves transparent background where you may have lost background making your corrections
b. Extension – Photoshop pretends it’s able to extend the background you lost and create something from nothing, and unless you’re working on a very low-resolution image, don’t expect it to recreate much, especially if there’s complex information.
c. Background Color – Photoshop simply extends your background with your current background color
7. Don’t bother with the Scale function here. I recommend waiting until you are completely finished with your work before scaling and use the Transform function or the Scale dialog.
Your box is no longer a quadrilateral or even a trapezoid (I love that word!). It is now a square. Pretty cool, eh (No, I’m not Canadian)? This process works well for photographs where the amount of correction required is modest.
Now, what about a real world situation? Let’s take a look.
1.Download the file, YellowChurch.jpg. Notice that it’s leaning back because of the camera angle. Let’s go straight to the Lens Correction filter.
2.Slide the Vertical Perspective control left and right to find the correction that will straighten up the building. My slider is a -26 for a good left and right side correction.
3.Slide the Horizontal Perspective control left and right to find the correction that will make the building “feel” flat to the camera. I used the set of 4 windows near the top as my guide and tried to get my grid lines to touch the top of each of the windows. My slider is at -24. At this point your YellowChurch file should look “corrected.” Use the Preview check box at the bottom to see before and after. Not bad. Now the original looks a little off, doesn’t it?
4.While we’re here, let’s take a second look at the bottom of the Transform dialog and select, Edge: Extension. Edge is where Photoshop tries to figure out what is missing from the photo due to the perspective correction and put back detail. It does a poor job with complex detail as you can see.
My suggestion? Return the Edge pulldown menu to Transparency and if you’re done with your corrections, select OK.
5.Crop out the transparent portions and you’re done.
Now it’s time to go back to your personal archives and see what kind of Lens Correction improvements you can make to your architectural and tabletop images.