«Penousal Machado Amílcar Cardoso Instituto Superior de Engenharia de Coimbra Dep. Eng. Informática, Uni. Coimbra, Polo II 3030 Coimbra, Portugal ...»
Generation and Evaluation of Artworks
Penousal Machado Amílcar Cardoso
Instituto Superior de Engenharia de Coimbra Dep. Eng. Informática, Uni. Coimbra, Polo II
3030 Coimbra, Portugal 3030 Coimbra, Portugal
Abstract: This paper is dedicated to the development of constructed artists, i.e., computer programs
capable of creating artworks with little or no human intervention. We make an analysis and critic of some of the most prominent work on this field. We give a description of the main characteristics that a system should have, in order to be considered a constructed artist. These characteristics include the capacity of making aesthetic judgments, which takes us to the origins of art and aesthetics, for which we present a brief theory. Finally we propose a model for the development of a constructed artist. This model has the capability of performing aesthetic evaluation, through the use of neural networks. The images are generated using a genetic algorithm, and represented using Fractal Image Encoding. This type of methodology allows the representation and, consequently, the generation of any type of image.
1. Introduction In this paper we will talk about the development of computer programs capable of creating artworks. We would like to stress the importance of this type of systems, capable of performing creative tasks, as a way of showing AI’s potential, and bringing AI closer to the layperson. The first applications of computers and AI to the field of the arts date from a long while. These applications had a stronger influence in music than in visual arts. This outcome is not surprising since the memory requirements necessary for image handling are substantially bigger than those necessary for sound.
Additionally, music theory is more developed and quantitative than theory in visual arts (Kurzweil 1990).
In section two, we make an assessment of the current “state of the art” in this field. In doing so, we specify a set of features that current systems lack, and that should be present. The third section pertains to the origins of art and aesthetic judgement, we give a short biological explanation to the devotion of humans to art and to how natural evolution favoured the appearance of art. We also give evidence to the sharing of aesthetic values with other species. In section four we propose a model for a constructed artist. This model overcomes some of the flaws that the current constructed artists exhibit. Finally, in section five, we describe the current state of development of our system, draw some conclusions, and point towards unexplored aspects in this field.
2. State of the Art The vast majority of AI applications in the field of the arts falls into two categories: Systems performing some sort of art understanding task, such as musical analysis, and systems that work as “intelligent” tools for human artists (Spector & Alpern 1994); and a new range of applications that is beginning to emerge, the constructed artists which “are supposed to be capable of creating aesthetically meritorious artworks on their own, with minimal human intervention.” (Spector & Alpern 1994). Restricting ourselves to the field of visual arts, which is our main field of interest, we will describe two approaches that have gained a vast acceptance.
Harold Cohen can be considered as the precursor of the rule based approach (Kurzweil 1990). His system, Aaron, is probably the most acclaimed constructed artist. The development of Aaron took approximately one decade, which gives an idea of the amount of work involved in coding the knowledge necessary to do artworks into rules. This set of rules is extremely valuable since it provides an accurate description of the artwork’s theory and structure (Kurzweil 1990).
The second approach is rooted in a computer program written by Richard Dawkins. This program evolves images of virtual creatures (biomorphs), through the use of a genetic algorithm (Dawkins 1987). From an initial random set of biomorphs, the user chooses the most aesthetically pleasing, the next generation is created through the mutation of the genetic code of the selected biomorph; thus, the fitness function results are supplied by the user; this technique was named interactive evolution. This methodology provides a way of achieving flexibility and complexity with a minimum of user input and knowledge of details. This “simple” idea served as a base for a large number of applications in several fields, including the field of visual arts (some of the examples are (Sims 1991), (Graf & Banzhaf 1995), (Todd & Latham 1992)). The main difference between these applications is in the coding of the images. Karl Sims, for instance, uses mathematical functions, coded in the form of Lisp S-expressions. The program generates the images from the SExpressions; mutation and crossover is also performed at the S-expression level. As far as we know, there is no evolutionary algorithm application that works directly with the images as bitmaps.
As we said before, these systems have been highly successful; yet, in our opinion, they have weaknesses that might prevent them from being considered constructed artists. Let us consider the characteristics that we think a constructed artist should display. The system should exhibit generic representational capabilities, thus, it should be possible to represent any kind of image. None of the systems described has this representational power, what hinders their generation ability. An human artist learns over time, a constructed artist should also be able to learn. Aaron is incapable of learning, Karl Sims’s system performs some kind of learning, since it gradually improves its performance, based on the user’s evaluation of the generated artworks; However, a human artist doesn’t start from zero, like Karl Sims’s system does1, in fact a human artist has access to the artworks made by others. He/she is able of learning from these examples, and eventually using them as source of inspiration. Integrating knowledge in a constructed artist will certainly improve its performance, it is not by chance that the most successful constructed artist, Aaron, is deeply knowledge based. To be independent from humans, a constructed artist must be able to recognize an artwork when it sees it, this will enable it to evaluate its own artworks and guide the generation process. Thus, a constructed artist must be able to perform aesthetic judgments. This is probably the most important task to achieve, unfortunately it is also the most difficult one. The issue of aesthetic judgment was first addressed by Plato, and since then the debates go on (Quintás 1987). There is a large number of theories regarding aesthetic judgment, and their relative values are unknown.
The lack of a strong theory of aesthetic value, poses several problems, including the issue of validation of the developed systems.
3. Aesthetic Judgment and The Origins of Art If we ask someone why he/she likes a certain painting, people will usually talk about the emotions or filling triggered by the artwork, the combination of colors, global composition of the painting, or, even more frequently, we will get the intriguing answer: “I just like it.”.
From our viewpoint, the assessment of the aesthetic value of an artwork is influenced by the “content” of the artwork (which can trigger emotions, etc) and also the “visual aesthetic value” of the artwork (color combination, composition, etc). The aesthetic value of an artwork rests on these variables and their interaction. It is possible to have an artwork that is visually pleasing, but whose content is displeasing, in fact many art styles rely on the mixed feelings caused by this discrepancy (e.g. many of Salvador Dali’s paintings). We also believe that these variables are independent. In other words, if an image has a high visual aesthetic value, it will have a high aesthetic value, independently from its content, and even if it is deprived of content2. We don’t mean that content isn’t important, we just mean it is not indispensable.
It seems clear that the way how content influences the aesthetic value of a given artwork depends, mainly, on cultural issues. From our point of view, visual aesthetic value, is directly connected to visual image perception and processing and is, therefore, mainly: biological, hardwired, and thus universal. The remainder of this section is dedicated to the support of the previous statement.
The initial population is generated randomly.
The existence of images deprived of content or meaning is controversial.
3.1 Art’s Origin “Why did man devoted himself to art?” To give answer to this question we will give an explanation of how natural selection favored the appearance of art. Natural selection should favor the fittest individuals in a population, so why should a seemingly useless activity as art be favored by it?
To the vast majority of the animals, the struggle for survival takes all their time. Only in their infancy they have time to playing and games. The same happened to the primitive man. Only from a certain point in history man begun to have spare time.
The first manifestation of art, as we know, is the “stone of Makapansgat”. This stone was recollected 3 million years ago by our ancestors, the Australopitecus. It was not created by them, nevertheless the single act of recognition of the forms of an human face in a stone is significant by itself. The first act of artistic creation, dates from 300.000 years, and is the representation of a female figure.
The appearance of art may be explained by the necessity of using other forms of communication other than gesture or speech. There are, however, other explanations that can be considered complementary.
The coordination of hand movements had a great influence on human evolution. When a prehistoric man devoted himself to painting he was not doing a fruitless activity: by painting he was also developing, and making an exhibition of, its manual ability. The exhibition of ability is important since it would, eventually, give him an advantage by making him/her more desirable for mating, considering that animals tend to choose the most fit individual they can for matting partners.
Intriguingly, some animals develop characteristics that are disadvantageous for their immediate survival, e.g. the tail of the paradise bird. The explanation for this paradoxical event is that: to be able to bear this disadvantage an animal needs to be very well fit. Consequentially animals displaying simultaneously: these disadvantageous features, and successfulness, would be favored as mating partners (e.g. Dawkins 1987). By dedicating himself to art, an individual is showing that he is highly fit, since he has time to devote himself to activities other than those necessary for his/hers immediate survival.
This set of explanations gives a reasonable justification for the devotion of man to art, they don’t justify, however, why do we find certain images beautiful, aesthetically pleasing, or artistic. As we said before, we believe that visual aesthetic value is directly connected to visual image perception, having biological roots. To justify this statement we must first show that there is a visual aesthetic value that is universal and independent from cultural issues, and thus hardwired. The analysis of children’s paintings allows us to observe the development of aesthetic. Between the ages of one and three years, the infants have difficulties to accurately control their hand movements. Among the ages of two to three years, they are capable of making powerful lines, soon simple images begin to emerge from the chaos of lines.
The next stage is the appearance of the first pictorial images. Usually, the first pictorial image is the human figure. This image is, also, always constructed in the same, rather puzzling way. It begins with an empty circle; in the next step bubbles are added to the inside of the circle; the bubbles are gradually transformed in eyes, mouth and nose; afterwards hair is included; Some of the hairs get longer, till they are transformed into arms and legs (Morris, 1994). Somewhere between the ages of six and twelve, these universal images begin to disappear due to educational influence.