Bitmap Strokes - Sample the world with your digital camera and paint with digital images
"We are always held captive by our analogies" -- R. Douglas Fields
When many reviewers first encounter Microsoft Expression Design, they naturally approach it from the perspective of an Adobe Photoshop user and do feature-by-feature comparisons of its layering capabilities, etc. In order to appreciate the full power of Acrylic and the scope of the skeletal strokes technology it is based on, however, it is necessary to get beyond the Photoshop analogy. Expression Design has many strengths that have no real parallel in Photoshop. As a musician, I find that sampler technology in music provides a much more powerful analogy for Acrylic's unique blend of vector graphics and pixel-based image manipulation tools.
When samplers came along, they fundamentally changed the way that music was created in the studio. You could record individual notes or instruments as digital samples and easily 'fly in' these recorded audio segments under complete computer control. You could take one digital recording and dynamically resample it, shifting its pitch so that it would sound like the various notes in a musical scale. Multiple samples could be used to faithfully reproduce the tonal range of an instrument, allowing you to 'play' virtual instruments with a range of tonality that was previously unobtainable. You could change the timber and loudness that a sample was played back with by controlling the speed and pressure that a key on a keyboard was played with. You could record the keyboard keystrokes as Midi files and then map different sounds to the notes that were recorded.
In Expression Design, the samples correspond to "Bitmap Strokes". You can scan in a 'digital recording' of a line drawn with a real pencil or charcoal stick and use this image to create a bitmap stroke that you can then draw or paint with using a graphics tablet or tablet PC. When you paint with a stroke, the path of the stroke and the stroke that was selected is what is captured, not the pixels that are layed down on the digital canvas. Expression Design is like a Midi sequencer program for images, giving you the freedom to easily change the shape, colour, thickness, transparency of a line in a sketch, clothe the 'skeleton' of the stroke with different images, all while retaining the structure of the image itself. Like samplers, you can change the strength of a sample by altering the pressure you apply while drawing with a graphics tablet stylus; Expression Design records the pressure variations, capturing the expressive nuances you impart as you draw, and allows you to edit the pressure profile later to fine tune your drawing. The brush stroke pressure can be mapped to either control the transparency (i.e. intensity) or the width of the stroke, or both. You can overlay multiple strokes to build up more complex 'tones' and redefine these collections as new strokes. Once you've defined a bitmap stroke, you can use it to define a multiple-view stroke that contains multiple variations of the stroke, providing a mechanism to introduce variety of line or shape.
With samplers, you can use the standard sounds that come with a sampler to get started, but the creative fun really starts when you start capturing your own sounds, turn them into samples and use them to create something new and wonderful. Expression Design is just like that - once you see how easy it is to create your own skeletal strokes and bitmap strokes, you can really start to grasp how powerful this software is. You are not limited to scanning in images of charcoal or pencil lines. You can use any image as a stroke. You can paint with flower petals. You can paint with asphalt, denim, anything you scan in. You can also paint with images of eyes, hair, smiles, ears, hands, arms, people, crowds, birds, dinosaur skeletons, drummers, rocket ships... ANYTHING. And then sculpt it, flare it, switch to another image, colourize it...
If you think of Expression Design as a vector graphics illustration application with an unprecedented ability to work with bitmap images and complex vector art as brushes, its pixel-oriented features can be viewed primarily as a creation environment for bitmap strokes to use as textures and brushes for the vector art, and for enhancing and polishing the vector images once they have been created. And, yeah, you can even use these features to do some of the stuff that Photoshop does so well too. But IMHO, that really is secondary to the vector graphics aspects of Expression Design. Being able to paint with the colors and textures of the world that you have sampled with your digital camera allows you to approach both art and photography in a completely different way, opening up new doors for creative expression.