Using Liquid Rescale GIMP Plugin for Resizing Images Without Distortion

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How to Use Liquid Rescale GIMP Plugin - Resizing Images Without Distortion

Liquid Rescale is a GIMP plugin designed to make it easy to resize images and change their proportions without the image becoming visibly distorted. It uses a technique called seam carving, which is also utilized by the application VSO Seam Carving, which I wrote about a while back. However, where the VSO application was a a stand alone piece of software, Liquid Rescale is designed to work with GIMP and if you're already a GIMP user, then this may be a preferable option.

If you stretch or squeeze an image in GIMP normally, the image will be uniformly distorted with areas appearing stretched or squashed depending on how you're changing the image's size. Seam Carving seeks to avoid this issue by adding or removing parts of an image.

When increasing the size of a photo, Liquid Rescale looks for series' of pixels within an image that can be duplicated and used to fill the new space without forming obvious regular patterns. When reducing the size of an image, pixels are identified that can be discarded without adversely affecting the image.

You should be aware that even using seam carving, aspects of a photo may become slightly distorted, particularly when increasing the size dramatically, though the use of masks offers a degree of control to ensure that this doesn't affect the main subjects of an image.

The next few pages will take you through the process of installing the Liquid Rescale GIMP plugin and then using it to resize a photo.

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Download and Install Liquid Rescale

The Liquid Rescale plugin for GIMP on Windows comes with a convenient installer, making it very easy to install. On OS X or Linux, you should follow the installation instructions supplied on the Liquid Rescale website.

First, download a copy of the Liquid Rescale Windows installer. Once the download is complete, you just need to double click the .exe file and follow the instructions. You will probably need to be logged into your computer with an Administrator's account in order to have the permission to install the plugin.

When the installation process has completed, if GIMP is already running, you will need to restart it before you can start to use Liquid Rescale. Now we can look at a simple example of how to resize a photo.

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Select and Open an Image

Now that Liquid Rescale is installed in your copy of GIMP, you can open an image and add a mask that will ensure that the most important aspects of the photo preserve their appearance after the image has been resized.

Go to File > Open and navigate to an image that you would like to try resizing and select it before clicking the Open button. This technique works better with some images than others, so you may need to experiment to get a feel for when it is likely to be most successful.

With your image open, go to the Layer menu and at the bottom there should be a menu item named Liquid Rescale which you should  click on. This opens the Liquid Rescale dialog with a thumbnail of your image prominent. You'll see that there are quite a few control options spread across several tabs, but we're just going to use the Width and Height controls and the Feature preservation mask for this basic example.

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Add a Preservation Mask

Before we rescale the image, we need to mask the most important elements to ensure that these are not distorted in the final image. For example if you had a person stood in the foreground of a photo of a landscape, you would want to mask the person. In my image, I need to mask the large tree and the wall in the foreground and I will also mask a few of the other trees in the lower part of the photo.

In the Liquid Rescale dialog, click the New button in the Feature preservation mask area of the dialog. The dialog disappears and a smaller dialog appears asking you to paint a preservation mask on the current layer. Do not press the OK button until you have finished painting your mask.

If you look at the Layers palette, you'll see that a new blank layer has been inserted and this is what you need to paint on. In the Tools palette, you will also see that the foreground color has been set to green and you needn't change this. You can use any of the GIMP tools that you feel comfortable with to produce your mask, but I'm just going to use a hard edged Paint Brush and use the Scale slider to adjust the size as required.

You now just paint over the areas of the image that you don't want to be affected by the rescaling action. Don't worry about being really accurate, you can be very rough and imprecise in this step, as you'll see in my example image. When you're happy that all the necessary areas of the image are covered, click OK on the little dialog and the Liquid Rescale dialog will now reopen.

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Rescale Your Image

You can now carry out the actual rescaling of your image.

For the purpose of this example, change the drop down that is under the Height input field to percent and then change either the Height or Width box to 130. This will give a reasonable demonstration of how effective the plugin can be and you should be aware that the results may become less satisfactory as you attempt to make greater increases.

By default the Strength slider of the Feature preservation mask sets to 1000 and I would advise leaving this unchanged initially. You can always go to Edit > Undo after using Liquid Rescale and try resizing the image again using different settings. In my case, I increased this setting to 2000 to improve the quality of the foreground features.

Once you've set this, just click the OK button and your image will be resized. When it's completed, you can hide the mask layer in the Layers palette, by clicking the eye icon to the left of the layer thumbnail. If your rescaled image looks as you want, then you can save a copy, but if any elements look as if they could be improved, as said before, just go to Edit > Undo to change your image back to the original size and open the Liquid Rescale dialog again.

In my case, I edited the mask a few times before I was finally happy with the result and this is easily done if you need to also. You just need to click the Edit button in the Feature preservation mask area of the dialog and then paint in more areas on the mask layer. If you compare the mask shown in the image on this page with the mask on the previous page, you'll see that I've covered more areas of the foreground to prevent them being distorted. After editing a mask, you just apply the Liquid Rescale again as before.

If you go back to the first page, you can see the rescaled version of my image.