Masking images can be a tedious process, especially when edges are indistinct. Tree branches, leaves, grass, and other organic forms are perennial nuisances, while fur and flyaway hair are next to impossible to crop. Corel KnockOut (formerly available as Ultimatte KnockOut) aims to make such chores easier. Its sole function is to knockout difficult image selections.
As you might expect of a product with such a narrow mission, KnockOut’s interface is Spartan. In addition to pan and zoom tools there are eight selection tools. The two primary tools-Inside Object and Outside Object-let you indicate the areas that should and should not, respectively, be included in the knocked-out image. (Two similar tools do the same for shadows, should you want to include them in your final image.)
To define the “transition” area where KnockOut will work its magic, you must first draw the perimeter (with the Inside Object Tool) of the area that is plainly within the object you wish to select. Then, using the Outside Object Tool you circumscribe the entire object, including any questionable areas, such as where hair mingles with background colors. The result is two concentric selection marquees. The area between them is the transition zone. At this point you can select Process from the Edit menu and KnockOut will do its thing, guesstimating where the actual cut should be made. The result is an alpha channel mask for the selected object. (A separate alpha channel is created for the object’s shadow if you have applied the shadow tools.)
In theory, this is a simple, three-step process. In reality, it takes a bit more concentration (and sometimes consternation). First of all, it takes a steady hand to use a freeform selection tool to follow any path precisely. The instructions tell you to draw the lines “as close to the edge of the transition as is needed to insure that the colors through which the line passes are the same as the colors adjacent to the transition itself.” Easier said than done! Cramps in my mouse hand had me longing for the more helpful selection tools found in Corel PHOTO-PAINT and other applications. Why not provide a magic wand, magnetic lasso, masking brush, or color mask tool?
Once a mask is drawn, you can select Expand or Reduce from the menu to subtly adjust its size, but these adjustments affect the mask uniformly, so you still need to be fairly consistent with your initial selection. You can’t nudge it twelve pixels here and three pixels there. As with any masking process, harsh edges usually result from a simple mask-and-clip. Feathering a mask before clipping is a common way to achieve a more gradual transition between foreground and background pixels. Most graphics apps, including Adobe Photoshop and Corel PHOTO-PAINT achieve this by averaging a number of pixels (specified by the user) along the entire edge of the mask. Experimenting with the pixel range allows fine tuning.
Compare KnockOut’s results without feathering (left) to
results using the Feather Edge tool (center). The jagged white edges at left show why feathering is necessary. Corel PHOTO-PAINT results, using a more natural feathering method, are on the right.
By contrast, KnockOut’s Edge Feather and Shadow Feather tools require you to draw a lasso around the pixels to be feathered. This creates a number of problems. Ideally the feathering area will encompass the entire transition zone (between the inside and outside lines already drawn). If not, an abrupt change in the sharpness of the edge will be obvious where the feathering stops. If feathering is applied beyond the transition zone, excessive blurring of interior areas of the knocked-out object will result. But just how do you achieve a precise demarcation with KnockOut’s freeform lasso tool? It’s virtually impossible. It’s a mystery to me that KnockOut doesn’t automatically select the entire transition zone for feathering, then let the user indicate the number of pixels of variance desired to either side. Ultimately, I found that feathering always left the image blurrier than I would have liked.
The last of the selection tools are the Inside Syringe and Outside Syringe. These are intended for fine-tuning the selection if wispy or semitransparent portions of an object fail to come out clearly in your initial knockout. Because KnockOut bases its include-or-exclude decisions on the closeness of a pixel’s color value to those found within the indicated foreground and background areas of an image, it may fail to choose correctly when a pixel’s color value is too far afield. The Syringe tools let you pick up a color from a well-defined location and inject it into the problem area so that KnockOut can identify it properly on the next pass. Problem is, you must do this one pixel at a time. Give me a break! In my trials, just a single wisp of a horse’s mane comprised hundreds of pixels, and there were many wisps of mane that needed addressing in this way. I ultimately opted to let KnockOut discard much of the wispy mane. In my opinion, anyone who feels the need to adjust an image at the individual-pixel level should either reshoot the image or go to plan B. Nobody gets paid enough to mess with such minutiae.
A small wisp of horsehair comprises many pixels. To preserve
them, each must be injected with a color from the horse’s body. The black-and-white-edged squares indicate pixels already selected with KnockOut’s Inside Syringe Tool. A tedious process, at best.
While it took me a while to get a handle on its nuances, in the end, I wasn’t too displeased with KnockOut’s results. Still, I question whether they’re worth the additional cash KnockOut requires ($99 US). I wouldn’t mind if Corel just added these features to PHOTO-PAINT’s already estimable masking tools, but I think I can do well enough as is with the current crop.