Decompose: Remove Background From Your Images

One of the most helpful features that was introduced to Keynote with Apple’s last revision, was Instant Alpha. Being able to remove the backgrounds of images with solid-colored backgrounds is something that a lot of applications sometimes struggle to do. But what do you do when the back grounds get a little more complicated?

A few weeks ago an application by the name of Decompose was featured on MacUpdate’s MU Promo (I suggest subscribing to both MU Promo and MacZOT’s mailing list. It’s a great was to build up your Applications Folder on the cheap). Decompose is an application that lets you remove the background from an image by selecting the foreground, outline and background of the subject you want the background removed from.

When you open up Decompose, you must select the image that you want to remove the background from. From here, the steps are pretty straight forward to remove the background of your image. The top of the app consists of 11 buttons and two sliders. The interface isn’t the most intuitive I’ve ever used, but all the tools are laid out in a way that it is still simple to get the job done.

To start the background removing process, you must trace the contour of the object. There are 5 tools to help you do this (from left to right- Brush, Fill, Lasso, Rectangle, and Wand). I found that out of all the tools just using the brush and fill was the easiest. The Lasso wasn’t very helpful, the wand is a little too sensitive, and in my tests, none of the images had anything that was perfectly square or rectangular. Your experiences may vary. You can change the size of the tools with the slider that is under the tool buttons.

After you have finished drawing the outline of your object, yo must select the foreground of the object. The easiest tool for this is just the fill tool. Clicking on the little person who is filled in (the left-most button in the group of buttons with people on them) tells Decompose that you are now selecting pixels in the foreground. Assuming you have completely enclosed your object with the brush, filling the foreground should be simple.

The last step is to select the background. Clicking the person who is un-filled with a black background tells Decompose that the remaining pixels are the background.

To see your finished image minus the pesky background, click result. Matte will let you see the space that the object used to occupy. How accurate your result is depends on how much time you want to spend to outline your object as best you can. As you can see in my example, since I didn’t follow the contour of the building all that accurately, you can still see some of the sky in the result. If you do it quickly with no precision, your result will not be good. If you take your time, the result is pretty decent.

If there was anything I would add to Decompose, it would be a straight line tool. As you can see in my example image, the subject is a building. Trying to trace the straight edges of the building was a little difficult, and could have been made much easier (therefore more accurate result) if there was a straight line tool. Also, the zoom slider in the bottom left corner is quite sensitive, and when you zoom out, the image moves into the bottom left corner, instead of staying centered as you would think.

Decompose shows the object on a transparent background, and exports them as a .TIFF file.

In the end, Decompose v1.0.2 can produce quite good results depending on how much time you want to spend, and is an application that I will definitely be using in the future. You can pick up your very own copy of Decompose from Metakine for $29.99 USD.

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