Gimp 101: Perspective

August 5, 2009

One of the hardest things to take a picture of, in my opinion, is anything with parallel lines. Why? Because it’s so hard to get them to stay parallel in your photos. This is really obvious in photos of one of my favorite things: brick walls. There’s something so simple and beautiful about brick walls. But then I take a picture of one and it turns out like this:

Crooked lines make me sad

Can you see how the photo is “leaning”? The mortar lines are not parallel to the edges of photo, making the wall look a little, well, wonky… for lack of a better word. I’ll have you know, too, it’s not like this is a careless mistake on my part. I knew I was taking a photo of a wall. I knew I wanted those lines to be straight. So why couldn’t I do it? I have no idea. For some reason, at least for me, this is a lot harder to do than it sounds. There must be some sort of science behind this, but goodness knows I can’t figure it out, I have at least one completely wonky photo in pretty much all of my photowalks. Especially when I do city walking, like this walk was (in downtown Akron, Ohio, if you care).

Anyway, back to the photo. Can it be fixed? YES IT CAN!

First I open up the photo in Gimp, then I go to the Tools menu, select Transform Tools and then Perspective:

Tools Menu

So. I knew this Perspective thing existed for the longest time without having any clue how to use it because this seemingly useless dialog box pops up:

Perspective Dialog Box

What are you supposed to do with that? There’s nothing you can input, just buttons that don’t seem to DO anything! For weeks I got frustrated with it and just dealt with my wonky lines. Please don’t get frustrated like I did. Please ignore this dialog box, you don’t need to use it yet. Instead, you’re going to click and drag on the photo itself. The goal is to grab a corner and drag it around – Gimp will keep the three other corners where they are, allowing you to get your lines all lined up. That doesn’t make sense, does it? It’s easier to see in action, so grab one of the corners… in this case, I grabbed the top right:
Grab a corner

Then I started dragging it around until the mortar lines were parallel with the dashed lines that represent the edges of the photo… like so:

Line up the Lines!

Can you see how it’s coming together now? I took the liberty of adjusting the bottom right corner a smidge, too. I didn’t take any screenshots, so just trust me on this one: it was just a smidge. At this point, Gimp’s just basically giving you a preview of what it will look like when you complete the transform, so if your photo looks a little choppy, don’t worry about it yet. And this is when that stupid dialog box come back into play. Once you’re happy with your stretching of all the corners, now you click on that transform button:

Click Transform!

Hooray! The photo isn’t choppy anymore! And my lines are all straight up-and-down and stuff. Exciting! The only thing is, because I moved my photo around, it doesn’t have square edges anymore:

Eek! Photo doesn't go all the way to the edge!

That’s easily fixed with a crop, just make sure there’s no transparent parts (where you can see that gray checkerboard pattern) visible (btw, you can crop by either using the crop tool, or you can select the area you want as the final photo and then go to Image –> Crop to Selection). After adjusting the layers, my final photo looks like this:

Edited Wall

I admit that it’s still not perfect, but it’s a heck of a lot better than when I started and it only took me about 2 minutes total. Not too shabby!

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