Using GIMP to edit and scale images - Available for Apple, Linux and Microsoft

Using GIMP to edit and scale images - Available for Apple, Linux and Microsoft

GNU Image Manipulation Program (GIMP) is a powerful Open Source application that is available for Windows, Apple and Linux. While not as user friendly as Photoshop, you can't beat the price (free). Further, if anything really annoys you, you are free to change the program as you wish, sharing your changes with others, as the source code is provided. This is the basis of the Open Source philosophy.

Images from modern cameras and phones can often exceed the maximum allowed for this site (2.5MBytes) and out of respect for others, I'd recommend you aim to get your image size down under 200kbytes to reduce loading times. The images I post are typically between 40 amd 200kbytes. I've shown the effect of reducing the JPEG quality with the composite image of some native acacia flowers above. From left to right, the five images have the following quality factors (QF) and corresponding file sizes in kilobytes:

QF Size

90 17.5

30 5.6

20 4.2

10 2.7

5 1.8

As you can see, you can dramatically reduce the image size with little apparent degradation in image appearance, though this does depend on the image composition. Eventually the image becomes blocky as more and more detail is stripped out.

The following instructions may appear daunting, but that's probably because I've gone into a fair amount of detail. After you've gone through the process a few times, it is quick and straightforward to do. You might find too that your mobile phone, digital camera or tablet already provides you with a selection of image size options and may even provide you with the ability to crop and scale a full image to create a copy for publishing on the internet without deleting the original. GIMP will however provide you with far greater flexibility in scaling, cropping and determining what level of compression you can accept for your final image. Plus, if you like, you can go on to use its massive range of functions to make further corrections and improvements to your image.

First Download and Install GIMP on your computer from:

When you start GIMP, two windows will open, the editing window and the Toolbox. You can do many tasks using either. A nice feature of the Windows version of GIMP is the way it stays on top of other windows, rather than ducking for cover whenever you want to paste a picture into it.

With Linux, to get a GIMP window to stay on top of all other windows, you need to right click the GIMP window toolbar and select 'More Actions...Keep Above Others".

I'll cover two processes:

A) Cropping (which you may not need to do)

B) Scaling and exporting your image

A) Cropping your image

1) Load your image into GIMP either by copying and pasting the image into the editing window, or by opening it via the File..Open menu item.

2) Select the rectangular selection tool

Tools..Selection Tools..Rectangle Select

3) Crop the section of the image you desire by clicking and dragging the mouse pointer and then releasing it to frame the desired section. You can repeat this action until you get the section you want correctly framed or you can resize the frame by moving the mouse pointer near the frame border or corner until it changes from a crosshair to a triangle, when you can click and drag the frame or corner in or out. You can also click inside the frame and drag the entire frame to reposition it if the frame is the right size but not centred. (This takes a bit of practice.)

4) Now copy the framed area

Edit..Copy Visible

5) Load the cropped image into another GIMP window

File..Create..From Clipboard

B) Scaling and exporting your image

1) If you haven't a cropped image in readiness for scaling, load your image into GIMP either by copying and pasting the image into the editing window, or by opening it via File..Open menu.

2) Scale your image

Image..Scale Image

A Scale Image window pops up

(If you don't see this window, move the GIMP window to the side to check if it has popped up behind the GIMP window.)

I scale my images by Width/Height and use a size around 640x480 pixels. Just type in the width (or length) you desire and the length (or width) is scaled automatically when you press the enter key. (I also leave the Quality Interpolation setting unchanged at 'Cubic'.)

To finish the scaling process, click on the Scale button at the bottom of the Scale Image window.

3) Save (Export) the scaled image. (I use jpg, as it gives the smallest file size.) The process is slightly different for Linux and Windows.

3.1 Linux (and Apple?)

Select File..Export, then give your scaled image a name and extension (I use jpg) and then click on the Export button to convert the image and save it.

3.2 Windows

Select File..Save As, then give your scaled image a name.

You can either set the extension by including it as part of the name, e.g. (.jpg) or by clicking on the [+] Set Filetype (By Extension) and selecting what you want. An 'Export File' window pops up prompting you to click the Export button to convert the image. Do that and a "Save as JPEG" window pops up with a slider that enables you to increase the image compression by reducing its quality. If you select "Show preview in image window", you can see the effect of changing the quality on both the File size and quality. You may have to juggle open windows to bring the preview image to the front.

To reduce the size of the image with some reduction in quality, reduce the Quality setting. If you select the 'Show preview in image window' by clicking in the associated box, you'll be able to see how the image quality is impacted and resulting file size as you reduce the Quality setting.

Close all the GIMP windows.

If your phone/digital camera has a GPS unit, you might like to use ExifTool (available for Apple, Linux and Windows) to remove location and other information from your picture before posting it.

ExifTool Download site:

There are GUI and command line versions. I use the command line version thus:

exiftool -all= Imagefilename.jpg

This creates a backup of the original Imagefilename.jpg file by appending _original onto the filename and creates a copy of Imagefilename.jpg with all the information about how and where the photo was taken stripped out.

I'll look forward to some great pictures accompanying your posts!


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3 Replies

  • I use an iPad as my darkroom and photo editor and while no single App rivals Photoshop or GIMP, when Apps are combined...the results are truly amazing...

    Here are a few to get you started, some are free...SnapSeed, Laminar Pro, MetaBroswer/Editor, iPhoto, Adobe Photoshop Touch and Mobile, PhotoEditor by Avairy, PW Lite, Process, PhotoForge2

    and thousands more...

  • Thanks for these suggestions. Maybe in your next post, Chris, you could give us an example of a photo edited by one (or two) of your favourite apps? One you've done some "special effects" on?

  • great, helpful post. However new GIMP (2.8.16) you will need to "File> Export " your reduced masterpiece.

    Another great free progamme is Irfanview - great for resizing and renaming - including batches of pics. This might be Windows only.

    Good luck and keep them coming,


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