The Propeller Paint Engine interface. Click image for larger view.

Once there, you simply select your tools and get to work. When you're done, you click OK, and your painting is applied to your layer on top of what was already there while preserving whatever transparency that was there as well.

What's especially nice about this plugin is that you can use any image as a brush or brush pattern. The paint engine will allow you to bring images in and then "track" them as you paint, meaning that it follows the direction of your strokes, as well as pressure and tilt, if you happen to be using a pressure-sensitive and/or tilt-sensitive tablet and stylus.

A sampling of some of Propeller's preset brushes.

The range of effects you can create using Propeller are pretty much unlimited. Although the plugin doesn't ship with all that many brushes and patterns (108 brushes and 28 patterns), you can use any image of your own to paint with. Propeller can automatically colorize it to match one of the existing color palettes, or you can use the original color from the image. Propeller will allow you to modify the image just as you would modify any of the preset brushes, and it will allow for the same sort of tracking, pressure sensitivity, etc. that the presets have.

Tool control
When you first look at the Propeller interface, you see a very simple toolbar consisting of traditional paintbrush, eraser, color selector, magnifying glass and hand tools. To start working, you just select the paintbrush tools and apply your strokes. This is called ease of use.

For functionality, this program—er, plugin—offers a degree of control that's entirely uncommon in Photoshop filters.

To begin with, you have three primary tabs that determine how your stroke will look: Brush, Color and Pattern. Under each tab, you get a pulldown menu of categories containing various sets of brushes, color palettes and patterns. You can even create your own categories and add your favorite brushes (or patterns) or your own brushes (or patterns) to the collections. You can also modify color palettes by adding to them and then saving them as separate sets.

The Brush and Pattern palettes in Propeller

Each brush you can select includes a default patterns and color, but you can swap out colors and patterns as you see fit.

But these are only the beginning. You can also interactively control the stroke, effect and dynamics of each brush. Stroke controls include opacity, size, sweep and angle. Opacity, size and sweep and also be assigned ranges, and angle can be set to "constant" or "track." (Ranges come into play in Propeller's Dynamics engine, detailed below.)

For effects, you can choose from taper (none, edge, center, upper, lower), border (with options for color and thickness) and two other groups of effects. These include diffuse, bleed, spin and shake, with individual settings for each.

One brush with several different effects applied.
Effects modify the way a stroke appears, adding
taper, border, diffusion, bleed, spin, shake, etc.

Finally, we come to my favorite feature: the ability to control the dynamics of the stroke. The Propeller Paint Engine supplies a simple graph of input options corresponding to stroke parameters. For example, you can use speed to control stroke size, while pressure controls opacity.

To assign an input option to a parameter, you just draw a line from an input option to the parameter you want it to control. One input option (such as pressure) can control any number of parameters (such as opacity and color), but each parameter can only be controlled by one input option. To change which input option controls which parameter, you can cut the lines connecting the two with a little knife tool that appears as you mouse over the lines.

How well it works
This is a pretty solid piece of software. In the couple of weeks I've been experimenting with it, it hasn't caused me the least bit of trouble, at least not on my G4. In other words, it didn't crash, which is really something considering I've crashed twice in my HTML software just while writing this review. The paint engine performs quite well, although you will naturally see a slowdown in performance that correlates to the size of the brush being used.

I have only two negative comments about this software, and they're minor ones. First, it doesn't have multiple levels of undo. Second, the eraser uses whatever tool you currently have selected. Often this means you have to go back up through the brush hierarchy to find one more appropriate for erasing. (Erasing with the Pebble brush, for example, isn't a terribly efficient way to erase.)

The bottom line
Nowhouse Propeller Paint Engine is an excellent addition to the Photoshop artist's toolbox. It provides capabilities not found in other standalone programs, let alone Photoshop plugins. Its tools are easy to work with and quite effective, and the asking price of $60 is almost negligible. We give this plugin a strong buy recommendation.