Squaring up photos in Photoshop

These instructions are for Photoshop CS4. I usually straighten photos "by eye", but there's a more accurate (and probably faster!) way of doing it, by using the Grid.

The photo was taken in haste, and it turns out that the camera was not only tilted but not quite parallel with the wall that the picutre was hanging on. (It saves a lot of editing time if the photo is taken properly in the first place!)

A wonky photo 

To activate the Grid, go to View and check that Extras is checked -

Then go to Show and check that Grid is checked -

You can toggle the grid on and off with the keystroke Control+H.

To select the photo and get the "handles" for distorting it, use the keystrokes Control+A (select all) and Control+T (free transform).

If you're not comfortable with keystrokes, you can find Select All in the Select menu, and Free Transform in the Edit menu. (If you need to do a lot of straightening photos, it will save a lot of time to get used to the keystrokes!)

Ready to transform/distort

The "handles" are the little squares in the corners and centre -

To use the handles, hold down the Control key (not doing so will stretch the image), put the cursor on one of the handles, click the mouse, and move the mouse till the lines in the photo align with the lines in the grid -

That gets the vertical line on the right lined up, but it moves the line on the left slightly to the left - so another correction is necessary -

Note that these adjustments have lengthened the photo and thus changed the proportions of the area of interest - it could have been avoided by moving the handle to the left instead of downward.

Use the handle at bottom centre to get the "picture" back to the original proportions -

Now you can crop to get rid of the white areas -

The grid is useful for making the border symmetrical.

Control-H to turn off the grid, and it's done -

Another way of doing it is here - it uses the Measure Tool, which is hiding behind the Eyedropper Tool; clicking and dragging along something that should be straight; using the "Rotate Canvas - Arbitrary" command, and then using the Crop Tool. I've not tried it yet, but it could be a fast way of straightening crooked photos.