Defining New Strokes

The user simply drags out a stroke definition box in the middle of which is an L-shaped line (Figure 8). The horizontal part and the vertical part of the L-shaped line represents the stroke's reference backbone and the reference thickness respectively. The L-shaped line provides a scale for the new stroke, and everything within the box would be included as part of the stroke. If the orientation of the new design is not aligned with the reference backbone, the user...

Piecewise Continuous Anchoring

If N instances are given, it is theoretically possible to use N-1 anchor origins to define a deformation that would result in the N given forms at the corresponding aspect ratio factors. Just as in curve fitting, we would not fit a (n-1)th degree polynomial to a set of n points because of the over-crookedness of the resultant curve and the lack of localized control over the curve. Instead of determining the multi-level anchor origins which are the coefficients of the two continuous parametric...

Irene H H Lee

School of Music, Hong Kong Academy for Performing Arts strokes makes it particularly attractive in terms of storage size and transmission efficiency. Its efficient implementation is favourable for incorporation into windowing systems and page description languages. We shall demonstrate the various techniques with our drawing and animation system, Skeletal Draw, which uses skeletal strokes as the basic primitives. An animation sequence has also been made to show the effectiveness of creating 2 D...

What is a Stroke

Useful as they are for simple designs, constant thickness strokes cannot be compared to more general strokes for convenience and expressiveness. While it is possible to trace out the outlines of a brush trail every time (figure 1), this painstaking drawing method no doubt is a hindrance to the aspiring artist. It is also doubtful whether pictures of reasonable complexity can be managed if all the strokes are traced out this way consider modifying a few strokes in Figure 3 if the strokes are...

Deferred Application or

In the definition of a higher order stroke, we are faced with the question of whether to treat the appearance of the sub-strokes as geometric attributes which deform with the main stroke or just cosmetic attributes akin to pseudo-pen size in the final coordinate space 12 . The answer to this determines whether we apply the sub-strokes before defining the main stroke (sub-strokes being merely geometric objects of the main stroke) or whether we apply them after applying the main stroke (i.e....

Comics and Animation

One interesting application of skeletal strokes that we have been exploring is its use in comics and stylish animation production. Snoopy and the characters in 'The Yellow Submarine' are characters falling under this category 18 . Comics is a now a highly respected sub-culture in many countries especially in Japan. Works by famous comics artists like Tezuka Osamu 37 have even been studied and given literary praise. Pragmatically, comics publishing is also a mega-dollar business. Even though...

Review on Skeletal Stroke Deformation

The skeletal stroke deformation has been discussed in detail in 28 , here we will only briefly go through the main points but leave out the mathematical details and derivations. The skeletal stroke deformation is based on localized parametric coordinate system transformation along the stroke application path. A skeletal stroke is defined by specifying a reference backbone and a reference thickness on any arbitrary picture. The purpose of defining the reference backbone and thickness is for...

Outcome or the Process

The monitor screen is not a piece of paper and the digitizer not a pen. Although the brush and stroke metaphor is helpful for understanding the digital drawing process, it may not be wise to strive to model it completely. Since we are usually more interested in the final appearance of the stroke than the physical action of dragging a brush across paper, we might as well try to model the desired look of the stroke in the first place. Of course one could then argue that the mastering of the brush...

Strokes Skeletons And Envelopes

The constant thickness stroke is still the basic drawing primitive provided by most commercially available vector based drawing packages 34,39 . To create pictures like figures 2, 3, 17 and 19 with these packages usually involves scanning in an original copy (which has already been created on paper) or tracing out its outlines manually or automatically. Indeed, many impressive illustrations that fill the pages of manuals of many market-leading packages are there to demonstrate the package's...

Speed Lines for Motion Blurring

In both comics and animation, fast action is often represented by speed lines, which suggest the distance an object or character has travelled across the camera before its shutter is closed again. Motion blurring is particularly important in animation because it reduces temporal aliasing effects. Its method of generation in vector based cartoon has not been, however, a well addressed problem. One possible way is to employ temporal antialiasing techniques like stochastic sampling across the time...

Higher Order Strokes

A stroke can be defined to consist of other skeletal strokes, in which case the stroke defined would be a higher order stroke. Actually, a stroke can even be defined in terms of itself by first laying out the applications of a special stroke named 'self. Since the appearance of the stroke 'self' is insignificant, it is normally defined as a constant thickness rectangular stroke. It needs to be there for the user to specify the relation between the recursive applications and the entire stroke...

Rendering a Recursive Stroke

Rendering a recursive stroke explicitly by determining the resultant geometry is in general impossible. Since a recursive stroke is equivalent to an IFS (Iterated Function System) code (with a condensation set if objects other than itself are present in the definition) 3,4,5,6 , the attractor is often a fractal with a fractal dimension less than 2. We therefore have to resort to one of the approximation methods for rendering these fractals. The Escape Time Algorithm 4 would result in a clean...

Skeletal Strokes

The use of skeletal strokes 27,28 is a new realization of the brush and stroke metaphor. It does not use physical models (e.g. bristles of brushes or properties of paper) nor use repeated patterns as the basic drawing unit. Instead, an arbitrary picture and its deformation are abstracted into a skeletal stroke to draw with. This structured approach turns out to be far more general than those based on physical models. It is a rich framework for general picture deformation yet the only control...

Drawing with Skeletal Strokes

Drawing with skeletal strokes is similar to drawing with constant thickness strokes on other systems. To select a stroke to be used for a particular path, there is a repertoire of predefined or user-defined strokes to choose from in the menu. However, choosing from the menu is inconvenient, especially when artists are likely to use a variety of strokes interchangeably. To ensure quick switching between strokes, we therefore allow the binding of 40 different strokes to the numeric keys (together...

Controlling a PseudoD Stroke

We have demonstrated how to create an illusion of rotation by making use of the general anchoring mechanism. To perform that deformation, only one control parameter, the aspect ratio of the stroke, has been used. We could in theory control any kind of deformation of a picture with the aspect ratio alone. If different features in a picture are to change in different ways, however, it would be more convenient to have independent controls. easily set up an external control system by which users...

General Drawing Applications

We anticipate that skeletal strokes would have considerable impact on many drawing applications in fashion design where stylish bold strokes are often used in interior design where pseudo-3D strokes representing furniture and architectural objects can be laid out with ease in dynamic clip-arts which can deform dramatically beyond the limits of stretching, shrinking, shearing, twisting and bending. If implemented in windowing system kernels or page description languages like PostScript, the...

Animation with Skeletal Draw

Animation takes full advantage of the picture and deformation abstraction capability provided by skeletal strokes. The Skeletal Draw program has also been built with facilities to generate animation sequences. Traditional key-frame technique is used by Skeletal Draw. To create the key-frames, the user directly manipulates the characters in the scene. The system then calculates the in-betweens by interpolating Catmull-Rom splines. After the keyframes have been laid out, the program can do a...

Skeleton verses Envelope

Many drawing 2D warping packages allow the user to specify the deformation of a picture by reshaping an envelope around the undeformed picture. This technique has been advocated for applications in 2D animation in as early as the 70's 15 and is still widely used in the latest systems 32 . A coordinate system transformation based on envelope deformation is quite different from a skeleton based one. The former is much more well defined as the coordinates within an envelope can usually be...