Gimp Tutorial: Straighten and crop a photo
How to use Gimp to rotate a crooked photo and use the crop tool for a perfect framing.
Gimp is a faithful companion when it comes to straightening a crooked photo or changing the framing of a picture. Two of the most common mistakes when you shoot a photo in a hurry are the crooked horizon and an imperfect framing, often too wide, for fear of cutting off a part of the subject. In the following example we can see, on the left, the photograph as it was taken, on the right we see the same image after intervening with Gimp to straighten and crop the photo. In this tutorial we will explain what are all the steps to follow to get the same result in minutes with Gimp.
Straighten a photo with Gimp
We return from the sea, and we find out that in the photo of the friends, taken at the kiosk on the beach, thanks to the two beers drunk in company, the horizon is completely wrong and we have to fix it. Or we are photographing a parade of musical bands and a beautiful trio passes in front of us, however, the shot is completely wrong, as in our example image.
To straighten a crooked photo, we need to use the Gimp's Rotate Tool . Once selected from the toolbar, we have to click with the left mouse button on the photo that need to be straightened: a window called Rotate will appear at the top right of the Gimp's interface. At this point we can manually enter a rotation angle in the Angle box. The parameter can be formed by positive or negative values. Positive numbers are hourly rotation, negative numbers are anti-clockwise. Correct the angle until the image appears straight, then click the Rotate button.
Another way to proceed is to select the rotate tool , then click with the left mouse button on the photo, the rotation is applied by moving the mouse, while continuing to hold down the left button. It may take a while to apply a rotation with large resolution images.
Crop a photo with Gimp.
Once the image is rotated, you will see a gray-colored checkerboard on the corners. This is because Gimp is unable to guess the part of the image outside the frame, so you will need a small crop to eliminate it. On the corners you can see the "chessboard", that represents the missing image, in red we have highlighted the part of the photo that we want to remove. It could be better if you always try to respect the rule of thirds when you go to crop an image, you can read a guide here if you don't know what it is.
Now that we have chosen how to frame the photo, we have to select the Crop Tool
and set some parameters on the Tool Options.
First of all you should set a Fixed Aspect ratio, in this case we will use the classic 3:2, you can set anything you need but you should always remember to respect one of the standard aspect ratios, here you can read a tutorial that will help you to choose which is the better.
I also suggest you to activate the guides, in this case the Rules of thirds, so you can have a visual aid that will help you to choose the perfect crop. Once the Crop Tool is right configurated, you can click with left mouse button on the photo. Holding the button, draw a rectangle of the right size. One you have released the left mouse button you can change the size of the crop by moving one of the four angles (red circle in next picture) or move the whole cropped area moving the middle.
Once you will be happy with the framing, simply click the left mouse button inside the area, to confirm the crop.
Now you can save your perfectly straight and framed photograph. Obviously a good photo should have already been shooted correctly, but often the subjects are in rapid movement, or the shot must be done instinctively, without stopping to reflect too much. In these cases it is better to keep a little wider with the shot and correct later. Modern cameras have a resolution that will allow you to maintain an exceptional quality even if you have to crop a part of the photo, but don't exaggerate.
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