1. Field of the Invention
The present invention relates to an apparatus, a circuit and a method wherein an image is transformed by means of texture mapping.
2. Description of the Related Art
In the field of computer graphics, as a technique of transforming an image in a virtual three-dimensional space, a technique called texture mapping is used in which a model that is an object shape and is configured with a combination of triangles called a polygon is made and then an image is attached to the model. Here, in the case where the model is positioned farther than a camera viewpoint in a virtual three-dimensional space, the model is reduced in size.
On this occasion, texture mapping with less aliasing is executed by preparing in advance texture data in which the same image is made to have lower resolution in stages (discretely), and texture data whose reduction ratio is close to that of the model is attached to the model. Typically, an anti-aliasing method according to this technique is called the mipmap method, and texture data lowered in resolution in phases are called mipmap images.
If the reduction ratio in the original state in which an image has not been reduced in size is defined as 1.0 and the reduction ratio when an image has been reduced in size is defined as 0.0 to 0.999 . . . , in the mipmap method, image data with a finite number of reduction ratios reduced by ½n (one divided by the n-th power of two), such as 1.0, 0.5, 0.25, 0.125, 0.0625 . . . , are prepared as texture data in a memory. After that, if the reduction ratio of a model is, for example, 0.75, the mipmap data whose reduction ratio is 1.0 and the mipmap data whose reduction ratio is 0.5 are read out from the memory, and further, by linearly interpolating these mipmap data by means of the weighting addition of one half each, texture data whose reduction ratio is 0.75 are calculated (refer to Patent Literature 1, for example).
[Patent Literature 1] Japanese Patent Publication No. 2002-83316 (Paragraph No. 0004)
However, there have been such problems as the following (1) to (3) in executing anti-aliasing in a typical manner by means of the mipmap method.
(1) If the reduction ratio of a model is of other reduction ratios than mipmap data, anti-aliasing may not be appropriately executed, because two mipmap data sets are linearly interpolated as described above. Thus, there occurs aliasing or a blur in an output image.
(2) Since it is necessary to prepare texture data of input image, which have been reduced in size by ½n, processing time becomes longer and the scale of a circuit is enlarged.
(3) Since approximately twice the amount of input image is required as a texture data amount, such as an input image+(half the input image)+(a quarter the input image)+(an eighth the input image)+ . . . , a memory having large capacity is required.