How to Square Up Photos in GIMP

How to Square Up Photos in GIMP

In the past, I’ve shared tips for using Photoshop to manipulate digital images. Today, I want to tell you how to square up photos in GIMP.

Just What is GIMP?

GIMP stands for GNU Image Manipulation Program and it’s a free downloadable photo editor similar to Photoshop the way I remember PhotoShop (I last used PhotoShop 7.)

Versions are available for Windows, Mac, Linux and more, so there’s no reason you can’t download it.

It also includes an in-depth manual.

What GIMP is not is easy to use, but then Photoshop had a pretty steep learning curve, too.

It is great for graphic designers, photographers, and illustrators who prefer their software on their hard drives instead of in the clouds.

GIMP also offers one of the easiest ways to square up photos that I’ve ever used. That’s what I want to show you today.

How to Square Up Photos in GIMP

Step 1: Open GIMP

This is the window that opens.

There are the usual menu items across the top of the screen, but there’s also a window of option icons in the upper left corner. Those items icons are links to the same categories as the menu bar items at the top, so you have two ways to make selections.

I prefer the menu bar, but have also become familiar enough with some of the icons to use them, as well.

We won’t be using the windows at the right, so I’ll save those for another post.

Step 2: Open an Image

Once GIMP is open, open the image you want to work with.

From the FILE drop down menu select OPEN or OPEN AS LAYERS.

OPEN AS LAYERS allows you to add layers to your image if you wish, and gives you a little more flexibility. You won’t be using that to square photos, so it’s okay to simply open an image.

Step 3: Mark the Edges of the Image

Next, you need to mark the edges of the image to tell GIMP how to square the image.

To do this, place your cursor along the top ruler, left click, and drag a line to the bottom of the portion you want to straighten. See the dotted blue line at the bottom of the framed painting below.

Repeat this for the top edge.

How to Square Up Photos in GIMP

Then click on the left-hand ruler and drag a line to the left and right edges of the area you want to square up. When you finish, you should have four blue, dotted lines, as shown below.

I generally place the blue dotted lines so that a horizontal line meets a vertical line at one corner. For this demonstration, the lower right corner was already the most square, so that’s the corner I used as a point of reference.

You won’t always have such a clear choice. In such cases, frame the image as you would if you were cropping it.

Step 4: Select the Perspective Transform Tool

In the TOOLS drop down menu, select TRANSFORM TOOLS, then PERSPECTIVE, as shown below.

Your cursor changes to a shape with two short lines at right angles and a triangle. Position this symbol at one of the corners, then hold down the right-click button and drag that corner until it’s lined up with the two blue, dotted lines nearest to it.

Repeat this process until each of the four corners is square.

After you’ve finished lining up the four corners, check them. Changes made to one corner could affect the other corners, especially if your photo is very distorted. Make whatever adjustments may be necessary.

Step 5: Transform the Image

When you opened the Perspective Transform Tool, another window also opened on the right. This window tells you in decimals how much you’ve corrected your image, but unless you like numbers , the only things you need are the two buttons at the bottom.

The reset button is the magic Undo button if you decide not to keep the changes you’ve made.

If you do like the changes, click the transform button. GIMP then adjusts your photo and squares it up.

How to Square Up Photos in GIMP

Check the corners again after the transformation finishes. If you need to make further adjustments, follow steps four and five again.

Step 6: Export the Image

When you’re happy with what you’ve done, it’s time to save it.

But if you just SAVE the image, GIMP will save it as a .xcf file which only be opened with GIMP.

To save images as .jpg or other types of image files, you need to export the image.

To do that, select FILE, then EXPORT AS.

The dialogue box below opens.

In this sample, the image shows the same title and format (.jpg) as the original. You can export it like this, but if you do, you overwrite the original.

I usually either change the name of the file or export it to a different folder. You can also change the file format. There is no right or wrong way to do this, so do whatever makes the most sense to you.

When you’ve made the changes in name, file type, or destination, click EXPORT at the bottom of the dialogue box.

The last dialogue box to appear is this one. You can set the quality of the exported image. I set mine at 100 (high quality) because I’m never sure how many ways I may need to use the image in the future.

The higher the quality, the larger the file.

You can set and save your own defaults if you wish.

When you’re ready, click EXPORT and your squared up image is exported. When the process completes, you can close the program or open the next photo to square up.

One Last Note

When you quit GIMP, you will get a dialog box like this, warning you that changes have been made but not saved.

I rarely save changes, because I prefer not to make changes to the original image. But you can if you wish.

How to Square Up Photos in GIMP

That’s How I Square Up Photos In GIMP

GIMP does take some getting acquainted with, but I’ve yet to find an easier way to square up photos. It works with framed art, as you’ve seen here, but also allows you to adjust potential reference photos before distortions get into your art.

It’s not a one-size-fits-all solution, but if you take the time to learn how to use it, it can save you a great deal of time and possible heartache in the drawing process.


  1. Terry Holahan

    I always save a 2nd copy of the original (Save as…, for example Horse to Edit) then close the original.
    I make whatever changes I want to the “to Edit” copy and when I’m happy with it, Save as, e.g., Horse Edited [Date} or Horse Edited Use This.
    I find the “Use This” moniker very helpful! “Final Edit” also works well as a reminder.

  2. Michael Farris

    Step 3 does not work. I’m not sure what “place your cursor along the top ruler” means. I have placed my cursor on top of the ruler, above the ruler, and below the ruler. I have placed it at the extreme left on the ruler, extreme right, and at various places in between. It doesn’t matter; I never get a line when I drag my cursor down. Am I supposed to have a specific tool selected when I do this? Clearly, from other responses, other people are making it work.

    1. Michael,

      I’m sorry to have caused confusion.

      There is no specific tool necessary before you can use this function except a mouse that has a right click button.

      However, I’ve found that GIMP can sometimes be twitchy. There have been times when I had to click on the ruler more than once before I could drag a line.

      One other possibility is that GIMP has been upgraded since I wrote this article in 2020 and that things have changed since then.

  3. Michael Farris

    Step 3 says “To do this, place your cursor along the top ruler, right click, and drag…” After half-an-hour of right clicking and dragging from every position I could think of on both the horizontal and the vertical rulers, I decided to try a left click. It worked on the first try.

    1. Michael,

      Thank you for the update. I tried that and you’re right. It does work!

      I also tried right-clicking and that didn’t work, so there has to have been some change since I first wrote the post. I have updated the post, by the way!

      Thank you for bringing this to my attention.

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