Smart scaling with Content-Aware Scale

New to Photoshop CS4 is its Content-Aware Scale tool which allows you to transform an image in a way that you’ve never been able to do before in Photoshop. The technology itself has been around for some time and you may have been familiar with the website rsizr.com which offers content aware scaling as an online service. However, the feature is now built into Photoshop making it a readily accessible tool for images large and small.

In this post, I’ll explain how to use content aware scaling and how to protect areas of your image from being distorted in the process.



Step 1
To see the tool at work open an image in Photoshop CS4 (this feature is not in other versions of Photoshop), double-click the background layer to turn it into a regular layer and choose Edit > Content-Aware Scale.



Step 2
Notice the sizing handles on the image. Drag from one side inwards and watch what happens as you do so. You’ll find that the image shrinks in size, but most of the information in the image is still there - the image is made narrower but key elements in it are not squashed up.

If your image includes people, click the person indicator on the toolbar so that it is not pressed in - when the indicator is flush with the toolbar the option is selected. This protects people by recognizing skin tones and ensuring that they are not distorted by the effect.



Step 3
You can also protect elements in the image using an alpha channel mask. This technique is handy if you have areas of the image that you want to retain at the expense of other areas and it can also be used to protect people in the image.

Make a rough selection around the area that you do not want to be affected by the scale effect. A good tool to use is the Lasso tool - select an area and hold the Shift key to make a second selection over another area, if necessary.

Choose Select > Save Selection, type a name for the selection, such as detail mask, make sure that the Channel is set to New and the operation is set to New Channel and click Ok. Press Ctrl + D (Command + D on the Mac) to deselect your selection.



Step 4
Now choose Edit > Content-Aware Scale and from the Protect dropdown list on the toolbar, select the mask you just created. Scale the image and notice that the masked areas are protected from being damaged as the image shrinks in size.

Content-Aware Scaling is a handy way to change the aspect ratio of an image. For example, you can turn a landscape image into a square image and close up the space between people in a photo if they are a long way apart. It also works in reverse and you can use it to make an image larger. You may need to do some work with the clone tool to repair small areas of the image damaged as the result of the scaling but typically the tool does a very good job.

If you don't have Photoshop CS4 then head, image in hand, over to rsizr.com and give the online tool a try. Here is an earlier post I wrote on the Rsizr tool.

Rsizr - Image scaling on steroids

While Photoshop, Lightroom and Photoshop Elements can resize images for you, only Photoshop CS4 supports content aware scaling. I'll talk about this new feature in Photoshop in another post but if you're interested in playing with content aware scaling and you don't own Photoshop CS4, check out Rsizr.com

Rsizr resizes images by removing the unnecessary content from them or by stretching neutral areas of the image to make the picture bigger. It’s worth a visit just to see it at work.


Start by uploading an image that you want to resize. This should be a JPEG, .PNG or GIF file with a height and width of less than 2,880 pixels – in practice, so you can see what's going on quickly, upload an image sized smaller than this.

Once the image appears in the dialog you will see tabs with buttons for various functions including the File Function tab, View functions, Resize and Retarget functions.


The program uses a seam carving technique to remove portions of the image. To get started drag the horizontal slider in the top of the window in to the size you want the image to be resized to. Click the Retarget button and watch as the seams are created (they're the red marks you can see in the image) and the file shrinks in size.


Once the seams have been created, you will see a set of sizing handles around the image which you can use to resize the image either to make it wider or narrower.


You can protect areas of the image or mark them for deletion by clicking the Preserve or Remove indicators on the retarget functions tab and paint over the area to keep or remove.


You might do this, for example, if you see some distortion in the resizing process and want to protect key portions of the image.

The rescale and crop tools are similar to what you're used to using in your photo editing software - it's the retarget option which is unique.

If you're interested in learning more about seam carving technology, visit: www.seamcarving.com to see a video describing it.

Stop Press! There is a cool plug-in available for the Gimp which brings content aware scaling/seam carving to the Gimp. For more information and to get the download, check here: http://liquidrescale.wikidot.com/ and note that the Gimp version is called Liquid Rescale! Just in case you thought there weren't enough ways to refer to the same thing.