ACKNOWLEDGEMENTS
I would like to thank my advisor, Dr. Davis, for all of his time and support. He provided the inspiration for Impressionist Paint, and proved very helpful while working on both the artistic and programming sections. Also, Dr. Kundert-Gibbs and Professor Wang were very supportive in brainstorming ideas and problems solving.
My fellow Digital Production Arts students were always encouraging, patient, and extremely helpful. I am grateful for their friendships and appreciate all they did to help me throughout my thesis work.
Most importantly, I would like to thank my family for their constant love and support.
TABLE OF CONTENTS
Page
ABSTRACT
ACKNOWLEDGEMENTS
LIST OF FIGURES
CHAPTER
1 INTRODUCTION
1.1 The Artistic Role of the Computer
2 HISTORY
2.1 Impressionism
2.1.1 Stylistic Characteristics
2.1.2 Subject Matter
2.1.3 Brush Stroke Variation
2.1.4 Artistic Portrayal of Lighting and Depth
2.1 Monet, an Impressionist Artist
2.3 Stylistic Focus for Replicating Impressionism
2.3.1 Non-Photorealistic Techniques
2.3.2 Paint Effects
2.3.2.1 Stroke Components
2.3.2.2Types of Strokes
2.3.2.3 Preset Brushes
2.3.2.3Auto Paint
2.3.3 Particle Systems
2.4 From Painting to Animation
3 IMPRESSIONIST PAINT: THE PROCESS
3.1 Early Attempts
3.2 Impressionist Paint
3.2.1 Replicating the Impressionist Painting Process
3.2.2 General Overview of Impressionist Paint
3.2.3 Limited Modeling
3.2.4 Painting Strokes
3.2.5 Combining Image- and Object-Based Techniques
3.3 Graphical User Interface
3.3.1 Adjusting Curve Length
3.3.2 Assigning and Maintaing Belivable Brush Sizes
3.3.3 Stroke and Curve Imperfection
3.3.4 Creating Idiosyncrasies With in Curves
3.3.5 Choosing A Brush
3.3.6 Controlling Stroke Coverage
3.3.7 Shadow Style
3.3.8 Painting the Object
4 IMPRESSIONIST PAINT: tHE IMPLEMENTATION
4.1 Imppaint
4.2 Prepaint
4.2.1 Creating Nodes
4.2.2 Adding Particle Objects to Point Emitters
4.2.3 Per Particle and Emitter Attributes
4.2.3.1 Emitters
4.2.3.1.1 Mid Emitter
4.2.3.1.2 The Ref Emitter
4.2.3.1.3 TheHishadEmitter
4.2.4 Prepaint Nodes and Attributes
4.3 Paint
4.3.1 Creating Curves
4.3.2 Curve Variation and Uniqueness
4.4 Brushattr
4.5 Shadow
4.5.1 Beginning Shadow Calculation Option
4.5.2 Constant Shadow Calculation Option
4.5.3 Calculating Shadow Colors and Placement
4.5.4 Determining Highlight Color and Placement
4.6 Moving On - Animating the scene
4.6.1 Understanding Stroke and Object Organization
4.6.2 Scaling Objects
4.7 Voila, Rendering the Scene
4.8 Post-Processing
5 CASE STUDY
5.1 Modeling for Impressionist Paint
5.2 Creating and Painting Scenery
5.3 Creating the Character
5.4 Texturing Objects
5.5 Editing the Scene
5.5.1 Brush Sharing
5.5.2 Creation of Additional Procedures
5.5.2.1 Altering Stroke Attributes
5.5.2.2Automatically Changing Brush Attributes
5.6 Discussion
5.6.1 Maintaining Proper Object Proportions
5.6.2 Hiding the base object
5.7 Animating The Painting
5.8 Post Processing
6 CONCLUSION AND FUTURE WORK
6.1 Incorporating Impressionist Paint in the Production Pipeline
6.2 Expanding Impressionist Paint to Work on Different
Surface Types
6.3 Animation Exploration
6.4 Conclusion
CHAPTER 1
INTRODUCTION
With the progress and popularity of computer graphics, can computer generated images be considered art? Artists intendto express a feeling or make a statement. For a painter, the physical aspect of applying paint to canvas, controlling the movement of the strokes, the quick spontaneous application of paint, or the detailed controlled strokes he makes determines the mood, style and outcome of the painting. Art is not created by accident. Good communication, art, and design are no accident. Fostering training intent and insight enhances design, which in turn builds bridges between truths, bringing us closer to how we think, feel and decipher images. Successful design brings us closer to cultural, personal, and aesthetic awareness [WATS02].
The computer does not create art; instead, the computer is used as a tool, just as an artist used a paintbrush, to create a successful work of art. The computational power of a computer creates new pathways for artistic experimentation. For example, a standard computer animation consists of thirty frames per second. In order to create a thirty second animation, an impressionist painter would have to complete nine hundred paintings, which is more than most artists create within their lifetime. The time involved in creating this large quantity of paintings reduces the feasibility of a single painter’s creating an animation. However, the use of automated steps to replicate the methods of the artist makes creating a stylized animation an option. Maya, a popular program used to create animations, provides an environment in which to experiment with using the computer as an artistic tool. In this work, we use Maya’s Embedded Language (MEL) to create Impressionist Paint -- a group of Mel Scripts that utilize the strengths of the computer to create an impressionistic style of animation while allowing the user to control the artistic decisions throughout each step of the painting process.
While creating non-photorealistic techniques is a popular area of computer graphics, impressionistic animations have rarely been seen. Often, transitioning from the canvas to the computer results in a loss of the artistic beauty of impressionism. The computer tends to relate objects with a harshness the impressionist painter avoids.
Our method focuses on retaining the stylistic sense of the impressionist painter while allowing the computer to automate repetitive tasks such the application of strokes and shading. Rather than using post processing or creating a renderer - which metamorphasizes a scene into an impressionist style painting, we seek to provide user/artistic supervision and control during the creation of a scene through an interface that provides the user a variety of choices to manage the application of strokes applied directly to the surface of objects within the scene. The resulting strokes are easily editable and are automatically repainted as necessary throughout the animation to maintain the users specifications.
Using our intuitive method for creating an impressionistic scene allows the user to be the artist and the computer to be a tool used to automate time-consuming tasks that normally prevent impressionism from being a feasible animation style. The goal of the final system is to ensure the resulting animation retains the subtitles and softness of impressionism.
CHAPTER 2
HISTORY
2.1 Impressionism
In order to recreate the impressionist painting style, the rules, guidelines and classifications of the impressionist style must be studied and adhered to. Although style appears to be highly individualized, it still follows these basic guidelines.
- emphasis on painting of light and the influence of light on objects
- color palette consists of mainly primary colors
- avoids the use of black
- avoids harsh outlines
- paint strokes intermingle between objects
- fast application of paint
- relies on visual color mixing
- utilizes everyday subject matter
“The impressionist style of painting is characterized chiefly by concentration on the general impression produced by a scene or object and the use of unmixed primary color and small strokes to simulate actual Reflected light.” [GRIF94]
2.1.1 Stylistic Characteristics
The common impressionist color palette consists primarily of bright colors. For a short period of time, impressionist artists used only primary colors. Instead of mixing the colors on the palette before applying the paint, as was traditionally preformed, the colors are placed directly on the canvas. As the layers of paint build up and brush strokes overlap, the colors began to mix. The impressionists allowed the viewer’s eye to complete the color mix. As the impressionist style progressed, the color palette was widened.
The impressionist artist works very quickly, adding a look of spontaneity to the brush strokes. The overall style is much brighter and airier than previous styles of painting. Impressionists do not try to blend their brush strokes together in order to create a smooth surface appearance; instead, the individual strokes are short and broken. The strokes can be viewed individually or collectively to create the composition.
2.1.2 Subject Matter
Impressionist artists focus on painting the light in the scene and its interaction with the subject matter. Their techniques provide a look of a fleeting glimpse, or the way a scene would appear just before your eyes focus. Harsh outlines are not used to delineate forms; instead, color and stroke movement defines the objects.
Another departure of the impressionist movement was in turning away from painting religious themes; impressionists focused on scenes from everyday life. Landscapes, social events, and nature scenes provide inspiration and subject matter for the impressionist painters. Advancement in the creation of paint allowed impressionist artists to move from their studios to the outdoors. As the impressionists moved away from a realistic style of drawing and painting, the artists tried to capture their subject matter in a manner that differed from the realism of the camera. The subject is often abstracted, with the artist focusing on the movement of light and color throughout the painting.
2.1.3 Brush Stroke Variation
The impressionist artist’s movements are based on intuition and not on a mathematical description. Even the manner in which the artist loads the brush influences the look of the paint stroke. Often times in impressionist works, the thick application of paint reduces the appearance of individual brush hair patterns within the painting. The reduced patterning enhances the need for paint stroke variation, which provides a challenge to recreate via the computer.
A challenge arises in the linear form of the brush strokes. Brush strokes are never perfectly straight lines and each stroke differs in length and width. The amount of pressure used to apply the strokes and the individual stroke variations combine to create the overall look of the object. Each of these minute details must be taken into consideration in order to create a resemblance of impressionism.
2.1.4 Artistic Portrayal of Lighting and Depth
The impressionist artist also does not rely on a mathematical formula to portray lighting and shading. The relationships between the objects and the light are strengthened by the artist’s shading choices. Oftentimes there are inconsistencies in the shading of a painting. Portions of an object that convey important details may not be covered in a physically correct shadow to avoid concealing that detail. Areas may be represented darker or lighter than they should be to lead the viewers eye to a certain area of the object or from position to position throughout the composition.
To suit their purpose, impressionist artists manipulate lighting and shading. Shading is used to emphasize detail rather than solely representing areas receiving various amounts of light. Shadows are limited to areas that do not contain pertinent details. Shading is used to create depth by separating layers in artworks, and solidifying the forms.
2.2 Monet, an Impressionist Artist
Monet, arguably one of the most accomplished artists of the impressionist movement, painted a wide variety of pieces depicting nature scenes. He also completed the same subject matter at incremented time periods throughout the day. The resulting set of paintings each have a unique color scheme and capture the subject matter under a particular lighting.
As shown in figure 2.1, Monet’s works have been described as being full of spontaneous, active brush strokes, juicy impasto pigment, and a shimmer of light and vibrant color [SPRO92] specifically the style we seek to emulate using non-photorealistic rendering (NPR) techniques.
Figure 2.1Example of impressionist painting
2.3 Stylistic Focus for Replicating Impressionism
The previously mentioned impressionist ideals offer a guideline for creating computer-generated scenes which can be used in animations. Specifically, the following impressionist characteristics are key to creating a computer generated impressionist scene:
- unique brush stokes
- influence of light on objects
- color palette consisting of mainly primary colors
- color mixing techniques
- black and harsh outlines avoided
- intermingling of paint strokes between objects
Later, we will focus on the importance of each characteristic. First, in order to formalize the rules of impressionism into a procedure using computer graphics.
2.3.1 Non-Photorealistic Techniques
One of the primary goals of computer graphics, has been to create photo-realistic objects and atmospheres; however, due to the inherent computational characteristics of the computer, the resulting objects sometimes appear “too perfect”. Since imperfections and variations within the scene play a significant role in recreating an impressionist style, we must turn away from traditional computer automated photorealism. Non-photorealistic rendering (NPR) techniques aid in fashioning the degree of variety necessary to produce a pleasing copy of the impressionist style.
Non-photorealistic rendering, has become a focus of intensive interest and study in computer graphics.
Non-photorealistic rendering brings art and science together, concentrating less on the process and more on communicating the content of an image. Techniques that have long been used by artists can be applied to computer graphics to emphasize subtle attributes, and to omit extraneous information. [GOOC01]
This field is unique because it blends the both the technical aspects of the computer with traditional forms of art. NPR has been applied to a variety of styles and effects. Past research efforts have dealt with finding the silhouette of the object and rendering it in a stylized way or with developing techniques that generate hatching. Renderers have also been created [MARK97].
Most NPR is either image- or object-based, or the two types of NPR may be combined. Particles have been used to signify direction and placement of two-dimensional strokes [MEIZ96], and image analogies have been used to “teach” the computer a painting style which is then replicated within the the desired two-dimensional image [HERT01]. A different approach derived from the idea of placing strokes directly onto the object surface, one such technique was entitled WYSIWYG NPR. This method was accomplished by using a consistent stroke width and projecting the stroke onto the three-dimensional surface of the object and then into texture space. An advantage of using WYSIWYG NPR is that the user views the object exactly as the object will appear once the scene is rendered [KALN02]. Our inspiration for Impressionist Paint stems from the works of [MEIZ96] and [KALN02]. We seek to provide an automated way to add brush strokes directly to an object while maintaining stroke variation and to color the strokes based on user commands.
2.3.2 Paint Effects
Maya’s Paint Effects proved useful when replicating the variations of impressionist paint strokes. A closer examination of Paint Effects provides an understanding of how these tools can suit our purpose.
Paint Effects provides a diversified means for the Maya user to quickly create scenes with foliage and organic objects, or to build complex environments. Forests and grassy fields are settings which may quickly be created via Paint Effects tools. The strokes may be painted onto a canvas, similar to paint packages like The Gimp and Photoshop, providing a two-dimensional appearance, or the tool can paint directly onto the exterior of three-dimensional models. This feature works on NURBS only (i.e. not polygons) and allows for detailed addition of strokes which adhere to the form of the model. Additional information concerning strokes is discussed below.
2.3.2.1 Stroke Components
When painting a brush stroke, a curve is created to determine the shape and placement of the stroke. A stroke is then created and attached to the curve, which is parented to the object. Once the new stroke is created, the curve is hidden.
The stroke consists of a group of changeable attributes, each of which may be altered to create the type of stroke the user needs. Resulting strokes may partially or entirely cover the surface. Properties of the brush strokes are conrolled by both the curve and stroke shape. The curve determines the smoothness of the line and the position of the curve on the shape, the basic construction of the curve as well as the length of the stroke. Curves may be overlapped to create an increased sense of depth.
Each stroke shape is connected to a brush node, which determines the aesthetic qualities of the stroke. The attributes of the brush node may be altered to create a variety of brush strokes. One such attribute, global scale, controls the overall scale of the object. The user can also choose to map a texture to the stroke, creating a closer similarity to an artist’s brush stroke. Additionally, the transparency of the stroke can be set to allow strokes underneath the current stroke to become visible.
2.3.2.2 Types of Strokes
Paint effects strokes are divided into two main categories: simple strokes and tubes. The simple stroke follows the path of the curve, and can be colored or textured. A tube stroke is similar to the simple stroke, yet is covered with tubular objects. In this way, the tubes provide a three-dimensional representation of the objects painted within the strokes.
2.3.2.3 Preset Brushes
Paint Effects contains a variety of preset brushes. The oil brushes are of specific interest to this research, since they most closely resemble those of an impressionist painter. In addition to the preset brushes, new brushes were created to provide greater variation between strokes. The new brushes are created in accordance with the different types of brushes an artist might use to paint. Figure 2.2 provides an example of a variety of paint effects brushes.
Figure 2.2 Paint Effects Strokes
2.3.2.4 Auto Paint
Paint Effects also has an auto paint feature that can entirely cover the surface with strokes. The user may choose to paint the NURBS surface according to the object’s grid or to add strokes randomly to the geometry. The number of strokes as well as any offset form the surface, may also be controlled by the user. The auto paint feature provides a precise method for covering a surface with strokes in a short amount of time. One of the unique options of the auto paint menu is clip edges, which allows strokes to extend past the boundaries of the grid. This extended placement helps to create a sense of interaction between objects in computer-generated animations.