The third author of this article has been developing various kinds of science art, one of which being computer lithography. In this article, some artworks of computer lithography are shown with its method of creation. It was developed through a collaboration of the present three authors, where Takaki proposed a basic idea of the computer lithography, Satake made computer programs for it and Tsuboya created artworks by the use of the outputs of computation (ref.1). This article begins with a definition of science art by the present authors, which works as a motivation of activities of art creation. Then, the method of computer lithography is explained and some artworks are shown.

What is Science Art?
The science art is an art which is created with a science mind in the artist. Therefore, the arts created by modern technologies, such as CG or the ones created by the use of laser or video equipments, are not included, if these technologies are established already. Note that application of established technologies can be made without science mind. Then, what is the science mind? It is a mental activity to understand how the nature is made up and how natural phenomena are going on.
In the art creation there are two cases where the science mind plays an important role. One is the case where an artist creates artworks while developing a technology for it. In this development the artist must necessarily consider of natural mechanisms concerned to the technology, and also of the relation of its result with human senses. In the computer lithography the mechanism of texture production in traditional lithography was considered and trials were made to simulate the texture production, such as the sand patterns, by computer.
The second case of science mind is seen when an artist tries to express a scientific concept as an artwork. A famous example of it might be The Persistence of Memory, by Salvador Dali, which is believed to be created with his interest in the special relativity. The Melancolia I by Albrecht Duerer might be another example, although it is not clear what kind of science mind he had in creating it.
According to the above definition of science art, it can be created by anybody, even by children, if they look for a new method of creation or they want to express some scientific idea.

Method of Creation of Computer Lithography.
The process of traditional lithography is as follows. The surface of a stone or an aluminum plate is divided into two kinds of regions; one with affinity to oil and one without it. When an oily paint is put on the surface, the regions with this affinity keep the paint and the rest regions reject the paint. A sheet of paper is put on it ad pressed to produce a designed pattern. However, small quantity of paint remains in the regions without affinity to oil, which form a pattern with scattered spots of paint. Thus, a texture pattern characteristic of the lithography is produced. These spots have various shapes depending on the process of handworks, such as sand grains, randomly branching shapes or network patterns.
In the computer lithography the formation of these paint spots are simulated by the use of cell automata technique, which is composed of the following processes. At the beginning a 2-dimensional plane with 2000x2000 pixels is prepared, and each pixel is given a black color with a probability p, thus we have a random mesh pattern. Then, this pattern is deformed according to a rule, which is set up artificially so as to produce a desired texture pattern. Here, the following two cases are tried.

Rule for sand texture:
(1) Four neighbors (right, left, above and below) of a pixel are observed.
(2) If 3 or 4 neighbors of a black pixel are black, this pixel is changed to a white one with probability q.
(3) If less than 3 neighbors of a black pixel are black, this pixel is unchanged and one of 4 neighbors is changed to a black one with probability r.
(4) This rule is applied number of times.
Figure 1 shows results of application of the above rule.


Fig. 1 (A and . Examples of sand texture for p=0.1, q=0.5, r=0.8, obtained after applications of the rule (a) 2 times and (b) 10 times.

Rule for large-spots texture:
(1) Eight neighbors (4 neighbors + oblique 4 neighbors) of a pixel are observed.
(2) If m or more neighbors of a pixel are black, this pixel is given a black color.
(3) If less than m neighbors of a pixel are white, this pixel is given a white color.
(4) This rule is applied number of times.

Figure 2 (a),(b) show examples of large-spots texture.


Fig. 2. (A and Examples of large-spots texture for p=0.4, m=4, obtained after applications of the rule (a) 2 times and (b) 10 times.

A computer lithograph is created by superposing a combination of several texture patterns with various colors on an arbitrary image, which is produced artificially or by any means.

Some Examples of Computer Lithograph.
Figures 3, 4 and 5 show some artworks created by the present authors along with expansions of their parts. Figure 3 was the first work for the present authors, which was created by superposing sand texture patterns on a microscopic photo of biological cell partition taken at Riken (Research Institute of Physics and Chemistry in Japan), and was shown at Riken Art & Science Exhibition 2005 in Kobe city. The other works were created since then.


Fig. 3. “The first cell division of C.elegans embryo0925Blue” with expansion of its part. Four kinds of sand texture patterns with different colors were superposed on a microscopic photo provided by Riken. (by courtesy of Riken, owner of the copyright of this figure).


Fig. 4. “Fruits” with expansion of its part. Four kinds of sand texture patterns were superposed on a photo of a fruit.


Fig. 5. “Kokorotomori snow (Heart and forest, snow)” with expansion of its part. Four kinds of sand texture patterns with different colors were superposed and combined with a sketch of a part of orange tree.

Fig. 6. Superposition of four sand texture patterns with different colors for creating “Kokorotomori snow”(Fig. 5).

Figure 6 shows a superposition of four sand texture patterns with different colors, which was used for the work “Kokorotomori snow” (Fig. 5). Note that this image is given a higher contrast so that colors are clearly visible, and is a little different from what was used for the work of Fig. 5. However, it will help to see how this work was created by superposing this texture pattern on a pencil sketch of oranges.

Concluding Remarks
A merit of computer lithograph is that it can be created without special training of traditional lithography or workshop space. Moreover, it may enable a new kind of artwork which looks like a lithograph but can not be produced in the traditional lithography, if a texture pattern unexpected in the traditional lithography is produced by a certain rule of the cell automata. Thus, the computer lithography will provides us a new tool for enjoying creation of a new kind of art. However, the status of the computer lithography is just at the beginning of development, and improvement in future is hoped.

References
1. K. Satake, A. Tsuboya and R. Takaki: A Trial of Computer Lithography, Bulletin
of Cultural Study on KATACHI (form), Vol.3, No.1, 1-11, 2007. (in Japanese)