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How To Resize Large Photos in OS X with GIMP

Here's how to use GIMP in OS X to resize images.

As digital cameras continue to produce improved shots -- and as the number of megapixels increases exponentially -- file size quickly gets out of control.

Here's how to use the free GIMP program for OS X to resize your huge images. That way, you can more easily share them and just generally deal.

First, download and install GIMP for OS X.

Now launch GIMP and locate the image you want to resize. For this example, I've chosen Flowers in Seoul.JPG, a photo that resides on my desktop. Right-click on the image and select Open With >> Gimp.

When the Convert to RGB working space dialog box appears, click Convert.

In the main GIMP window, select Image >> Scale Image.

The Scale Image window will appear. Under Image Size, you can toggle between pixels, percent, inches, millimeters, points, picas, and more. If you have a specific pixel width or height in mind, change either one (or both) accordingly. GIMP preserves the aspect ratio of your image automatically.

For example, if you change the width, simply click inside the height box and the calculation for the height will immediately appear. You also have the option to change the X and Y resolution.

As for quality, unless you have a particular requirement, leave the Quality set to default: Sinc (Lanczos 3).

In this example, I am reducing the image by one half of its original size. So I select percent in the dropdown box. I change the width to 50 and then let GIMP automatically fill in the height of 50 for me. Do what you want, then click Scale. This opens the Scale Image dialog.

Now you need to save your image. To permanently resize the image, select File >> Save. If you want to keep the original as it is and have the resized image, too, click File >> Save as.

Give your image a meaningful name, select a location and click Save.

Here, GIMP will prompt you to set the quality of your image. The higher the quality, the larger the file. I find 85 to be a decent compromise. When you’re done with your entry, click Save.

That's all there is to it. Quit GIMP by selecting File >> Quit.

Confirm that you indeed have the image and that it looks the way you expected. In this example, I saved the image in a folder I created called GIMP Pictures. I have both the original and the resized image.

Based in Southern California, Buzz Garwood is a senior contributor at BYTE. Follow him @buzzgarwood, or email him at

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