How to Resize an Image in GIMP on the Raspberry Pi
One of the most useful things you can learn to do on your Raspberry Pi is to resize an image. All computer images are made up of pixels, which are tiny colored dots. Several cameras produce images that are 4272 pixels wide and 2848 pixels high. High-quality images like that are great for printing photos, but if you just want to use pictures onscreen, quality comes at a price.
That level of detail requires a large file size, and big files can significantly slow down your Raspberry Pi. Often, you can use a lower quality image without noticeably affecting the end result, assuming your finished result will only be displayed on screen.
Here’s how you can resize an image using GIMP:
Click to open the Image menu at the top of the screen and click Scale Image.
A window opens.
In the Width box, enter the width you would like your final image to be in pixels. Press Enter when you’ve finished entering your width.
If you wanted to put a holiday snap on your website, you probably wouldn’t want it to be more than 500 pixels wide. Anything larger than that can be hard to fit into a web page design and might take a long time for visitors to download. If your screen only displayed 1024 pixels across, you probably wouldn’t want to use an image much larger than 800 pixels wide.
When you enter a new value for the Width, the Height is updated automatically, so the image stays in proportion and doesn’t become stretched. You can also enter a value for the Height and have the Width calculated automatically. If you want to be able to adjust the Width and Height independently, click the chain to the right of their boxes to break it.
Alternatively, instead of using absolute values for the width and height, you can resize your image to a certain percentage. Click the Units drop-down list box (it says px) and choose Percent.
The values in the Width and Height box will then be percentages. For example, you would enter 50% to shrink the image by half. The size of the image in pixels is shown under the Height box.
When you’ve set your size, click the Scale button.
At the bottom of the screen, underneath the image pane, you can see some information about the file, including the current zoom level, which is how much the image has been magnified or reduced for you to view it. If you set this to 100%, you can get an idea of how much detail is in the image now, and it's easier to edit too.
Resizing an image reduces its quality. This would be noticeable if you tried to create a high-quality print of it later. Don’t overwrite your existing image with a resized version. Instead, save your resized image by choosing Save As from the File menu at the top of the screen and giving it a different filename.