Of all compositing tasks, the most difficult to get right is separating an object from its background. If the object is diaphanous, or, worse, fully transparent, it’s next to impossible to eradicate background colours using Photoshop or a comparable image-editor alone. This is when you need to reach for a dedicated tool like Corel Knockout – which now runs under both classic Mac OS 9 and Mac OS X. Because a Knockout job is invariably a part of a larger process – for instance, the creation of a digital composite-image – it’s designed to slot-in to the existing workflow as simply and discreetly as possible. So it’s no surprise when you launch Knockout to find that there are no Open, Load or Import commands – in fact, no way to get an image into the program using it alone (not even drag-&-dropping on the application icon works).
You have to install a plug-in in Photoshop (or a compatible program such as Corel Photo-Paint) and run this filter on a layer in the host application. Basically, you define an outside area that needs removing by using a selection, and do the same for areas that are inside, and need to be kept. This is done with a lasso tool, creating familiar “marching ant” selections. The Syringe allows you to add a single-pixel colour sample from the inside selection to the outside, to help Knockout retrieve difficult areas, such as fine hair.
The process can be repeated until you get the best result. New features in version 2.0 include support for CMYK images, a property bar, automatic outside-selection creation after defining an inside selection, and 99 levels of undo.
However, undo doesn’t seem to work on processing steps, only for changes in the selections. There are also new tools such as a polygon selection tool, and even an eraser and brush, allowing you to perform fine touch-ups in Knockout (again, undo doesn’t seem to work here).
Mastering the techniques involved doesn’t take that long, and Knockout 2.0 works well. Most impressive is seeing transparent objects flawlessly extracted from a background – even when the background is not a uniform colour. Knockout 2.0 does the business.