Step 5: Drag The Vertical Perspective Slider To Correct The Keystoning

Near the bottom of the column on the right of the Lens Correction dialog box is an option called Vertical Perspective, and all we need to do to correct our keystoning problem is drag the Vertical Perspective slider either left or right. For images where the building looks like it's leaning backwards, you'll want to drag the slider towards the left. As you do, you'll see the image in the preview area appear to tilt forward. The further you drag the slider, the more the image will tilt and as it does, the sides of the building will appear to straighten themselves out. Keep an eye on the sides of the building as you drag the slider and compare them with the vertical lines in the grid. When the grid lines and the building sides appear parallel to each other, you've corrected the keystoning:

If you need to move the grid around to line it up with one of the sides of the building, select the Move Grid Tool directly below the Straighten Tool on the left of the dialog box, then click and drag inside the preview area to move the grid as needed.

Step 6: Set The Edge Option To Either Transparency Or Background Color

By tilting the image forward, we've created a lot of blank space along the bottom of the image. We need to tell Photoshop how we want to deal with that blank space, and we do that using the Edge option at the bottom of the right column, below the Vertical Perspective slider. By default, the Edge option is set to Transparency, which fills the blank area with a grid pattern (which is how Photoshop displays transparency). You can leave it set to Transparency if you like or you can select Background Color, which fills the blank area with your current background color. There's also a third option, Edge Extension, which I highly recommend you don't use. Personally, I prefer to select Background Color because it makes it easier to see where the image needs to be cropped, which we'll be doing in a moment:

Click OK in the top right corner of the dialog box when you're done to exit out of it and Photoshop applies your adjustments to the image. Here's my photo after correcting the keystoning. The sides of the building are now parallel and it no longer looks like its leaning backwards. Notice that the blank area along the bottom has been filled with black which is my current background color. If you set your Edge option to Transparency, you'll see the bottom of the original image on the Background layer showing through:

Step 7: Apply The Free Transform Command If Needed

You may find at this point that the building looks a little short and stubby. In other words, it doesn't seem quite as tall as it should be. If that's the case, press Ctrl+T (Win) / Command+T (Mac) on your keyboard to quickly bring up the Free Transform box and handles around the image. Press the letter F to switch to Full Screen mode if you're currently working in a document window so you can see what you're doing, then click on the bottom handle and drag it down a short ways to stretch the image vertically until the building looks the way it should. Press Enter (Win) / Return (Mac) when you're done to accept the change:

Step 8: Crop The Image

As a final step, we need to crop away all the unwanted areas along the bottom and the sides. For that, we'll use Photoshop's Crop Tool. Select it from the Tools palette or simply press the letter C on your keyboard to select it with the shortcut:

Then, with the Crop Tool selected, click and drag out a cropping border. Everything inside the border will be kept while everything outside of it will be cropped away. Once you have an initial cropping border, use the handles on the top, bottom, sides or corners to fine-tune it until you've selected the area you want to keep:

Before you crop the image, go up to the Options Bar at the top of the screen and select the Hide option. This way, rather than deleting the area that gets cropped away, Photoshop will simply hide it, allowing you to undo the crop later and restore the entire image if you ever need to go back to the PSD file to access the original image on the Background layer (to restore the image after cropping it, go up to the Image menu and choose Reveal All):

Press Enter (Win) / Return (Mac) to crop the image, and you're done! Here's the original photo once again for comparison:

And here, after straightening the photo, repairing any barrel or pincushion distortion and fixing the keystoning problem, all within Photoshop's Lens Correction dialog box, is my final result:

And there we have it!