Consideration on the Photo-Realistic Rendering of Fruits by 3 DCG

Three-dimensional computer graphics (3DCG) is the technique of creating an image having a stereoscopic effect by converting an object in the virtual three-dimensional space into two-dimensional information. It is also possible to produce an image that cannot be distinguished from the real thing by using the 3DCG. 3DCG is expected for the application to visual representations very much. However, it is difficult to express the "freshness" of fresh food by 3DCG.Therefore, expressiveness of 3DCG is considered to be improved by overcoming this weakness. In this paper, we consider the photo-realistic rendering of fruits by 3DCG. The algorithm is implemented by using the Visual C++ 2010 and C on a personal computer. Through this trial, we hope to improve the representation in photo-realistic rendering by 3DCG.


Introduction
Today, researches and developments of three dimensional computer graphics (hereinafter referred to as 3DCG) and technologies related to 3DCG are extensively conducted.Among them, there is a field pursuing ultimate reality by making full use of rendering and bump mapping.One of them is a digital food, which is being studied for the future practical application.For digital foods, it is expected to solve problems related to food freshness management, disposal, development simulation of new products, and the like.In this thesis we will consider how to express the freshness of food as an example of cut apples [1][2][3].

Principle
In many cases, CG refers to images and images drawn with 3DCG.One of the reasons why various technologies using 3DCG technology such as AR and 3D printers are developed is high expressive power of 3DCG.However, it is difficult to express 'freshness' or 'organic coloration' of fresh foods, fresh flowers, etc. even with 3DCG expressive power.

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In this research, we explore what technology is necessary to express "freshness" and "organic coloration" which 3DCG is not good at.

Previous study
We used OpenGL to create CG.Modeling in OpenGL is performed by designating a set of vertex data and a rule connecting vertices.Note that since the shape of the model changes depending on the order of the given vertices, the order of the vertex data must be taken care of in the consolidation rule.Also, OpenGL does not have functions to create circles or surfaces.Therefore, triangle polygons and quadrilateral polygons must be arranged and their shapes approximated.Materials are set by mapping.Texture mapping was done to express apple skins.For the texture image, the image of the skin was cut out from the apple photograph (Fig. 1).Fig. 1: Model applying texture mapping.
Bump mapping was carried out to express fine unevenness of apple fruit.The image used for bump mapping was generated using image editing / processing software called GIMP (Fig. 2).Fig. 2: Model applying bump mapping.

Creation
This time I used Blender instead of OpenGL to create CG.Generally, creation of CG is generally not made by program only like OpenGL, but because there are many software to create sensually using GUI etc.I chose Blender because the concept is basically the same as such software.I studied how to become more real on my own from images in previous research.Compared with actual cut apples, dense expression is not done.In addition, CG has not removed core and its expression is not done either.Overall we can not feel the freshness.Solve these problems.

Modeling
In this time we will create ordinary apple and cut apples.First, we made ordinary apples from UV spheres and edited it to make cut apples (Fig. 3).The part with the leather expresses a smooth curve by increasing the number of divisions and the number of divisions is made smaller for the cut part so that it is expressed linearly.

Material setting
Material setting is done by mapping as in previous research.In the previous study, only texture mapping and bump mapping were performed, but this time UV mapping is performed.UV mapping is a part of texture mapping, and by attaching a texture to a twodimensional developed view of the surface of the object, the texture is stretched to the sterically wrapped part P -320 without being stretched.As a result, we were able to freely change the material and expressed it densely (Fig. 3).Fig. 3: Fabrication of map by UV development.

Result
The cut apple I made is as shown in Figure 4.I think that more realistic things could be made using means not used in previous research.However, the mapping looks more beautiful in the previous research.In OpenGL, the mapping associates the vertices of the image with the vertices of the object, so it is affixed as expected, but it did not work in Blender so it did not work.Also, it is impossible to say that the expression of freshness has become a sense as it will make it just fine.

Discussion
About realistic depiction of fruits by 3DCG I have been researching with awareness of the shape and color reproduction.From now on, it is considered necessary to investigate future research and evaluation methods of algorithms that make it possible to reproduce the structure of fruits finer.Also, people are affected by many colors.Although the syrup of shaved ice has the same taste, it feels like the taste is different only by the difference in color.There is also a psychological experiment that affects appetite and hangs glasses with blue film, which makes the dish look a little tasteless (Fig. 6).As you can see, I think that rather than putting emphasis on models to be created, understanding human visual information and using optical illusion will make it more realistic.It is easy but made around so that it looks more natural (Fig. 7).For comparative purposes keep an apple that is not mapped next to it.

Conclusion
In the expression pursuing reality, I felt that not only the solution of the technical problem of 3DCG but also the ingenuity of the production process is necessary.Since CG technology was developed, CG technology has grown rapidly, but it is a developing technique that still has many problems to be solved.In the future, as 3DCG technology advances, new technology applying 3DCG can be expected to be born.The advent of such technologies may bring big changes to our society in the future.