14 DAY TRIAL // Good photo manipulation is a complex, complicated process that at the high ends takes many years to master and many, many hours of hard work to achieve convincing results. This sort of job requires dedicated tools, many of which are professional, high-end applications. Of course, that need not always be the case, and at the lower level, there are many shareware programs that can let you achieve similar results. One of the harder things to do is the decomposition of images, taking out elements from them for placing in other images and making it look good. We're not talking about white objects with clear contours on black backgrounds, but those images of things such as hair blowing in the wind, where there are many small strands of hair that need to be separated from the background.
Given the complexity of this task, I was surprised to see a small shareware program that claimed to be up to the task, so I took Decompose for a ride.
What it does
Decompose is a program that makes it easy to decompose part of an image, so that it may be used in another one. Unlike tools such as the lasso and the 'magic' pen or wand or whatever it may be called in your particular program, that keep parts of the background along with the part you want to extract, Decompose only keeps what you want to keep.
On masks and transparency
Once I had downloaded the program and opened it up it became immediately clear what it does. This program simply makes use of alpha channels to keep the part of the image you want and make the background transparent.
Those familiar with alpha channels, know how this works, for those who have never heard of it before, the alpha channel or 'mask' is another grayscale layer, where black pixels indicate pixels from the image that are fully visible, full white pixels indicate pixels of the image that are fully invisible and any shade of grade represents partial visibility based on the shade of gray.
Using such masks is common practice, and they can be created in any decent image editing program.
How Decompose works
This program is basically an alpha channels made easy tool. You use painting tools to indicate which areas of the image you want to keep and thus fully visible, which areas are part of the background, and as such totally invisible, and which areas are contours, meaning that they contain both parts of the background and part of the image you want to keep.
After my first test I got the impression that this is a phony program that simply uses what you paint as a mask, simply slapping a gradient on the contour to make a nice fade from visible to invisible. That is not the case as I later found out.
Part of the problem is the tutorial on using the program. It tells you to draw around what you want to keep using the contour 'color.' While this is certainly the case for the image in the tutorial, for the image I used, the contour of what I wanted to keep was quite sharp, and as such the contour tool was not needed.
Despite what impression the tutorial might give, if an object has clear cut edges, there should be no contour color there, just foreground and background color. The contour shade should only be present in fuzzy areas, such as the edges of the dog in the tutorial.
To verify this I loaded a black and white rendering of an ape head I had and just drew a contour around it. As expected, the program was confused, as the difference between what I wanted to keep and the background was dead clear, but I had marked it as a contour. The resulting mask had almost no gray as the software was trying to interpret the 'fuzzy' area that was not there and failing miserably.
Magic algorithm
The algorithm the program uses to decide what pixels of the fuzzy are background and which are foreground may not be perfect, but it works pretty well. The masks it produces are by no means perfect, but they are damn good considering the amount of work you put into making them. As long as the logic of the program is understood and the painting is done with care, it should produce excellent results in most of the cases.
Best of all, if you open an image that already has a mask, it will automatically be converted into Decompose 'image/contour/background' terms and you can refine it, without having to do any additional ground work.
The Good
Makes creating alpha channels easy by using simple paint tools.
The Bad
Nothing bad about it, though the tutorial can be a bit misleading, especially for those who have never worked with alpha channels before and have no idea why the results are not what they expected.
The Truth
A very nice little program that does this job a lot better than most professional applications out there, who lack such a dedicated tool. It definitely worths a look if you find yourself working on lot of decompositions.
Here are some screenshots, click to enlarge:
