The present invention relates to a system for image representation of a real object using photographic images and a method thereof; and, more particularly, to a system for representing an image of a real object by using photographic images and extracting characteristics of a device collecting target object characteristics data, obtaining photographs of the target object by using the device, extracting characteristics of the target object though analyzing, and reproducing photorealistic images and a method thereof.
A term ‘image’ denotes a digital image or image data, and the image is classified into a photograph created by an image sensing apparatus and a photorealistic image created by a simulation result.
The photograph is a data set visible to human's sight by converting light energy to the visible data set using an image sensing apparatus. That is, the light energy radiated from a light source is reflected from a target object, and the reflected light energy is expressed into visible shape by converting the reflected light energy to visible data through the image sensing apparatus. The photorealistic image is produced by the present invention (refer to
Conventionally, in order to produce the photorealistic image of an object, an experienced person draws the object by using a painting system, or repeatedly performs mathematical calculation for realistic representation of the object based on the reflective characteristics rule by using an image synthesis system. Therefore, it takes long processing time to produce the photorealistic image. The reason to take such a long processing time is that the photorealistic image is produced by repeated retouching based on a person's experience or sense of beauty because there is no knowledge of a light environment influencing the color and reflection characteristics of the object.
However, if it is understood how light sources are distributed to the environment and how the lights are reflected from the object, the color of the object can be calculated mathematically.
Generally, the distribution of a light is expressed by a spectral power distribution function, and reflective characteristics of an object are expressed by bi-directional reflectance distribution function (BRDF). The real light source is irregularly radiated according to time, voltage or environment, but the variation of the light is not large enough for a person to recognize the color variation of an object in usual environments. That is, spectral characteristics of light can be defined by one time measurement when it is used for photorealistic images such as general movie or advertisement. However, the reflection characteristics of an object can be mathematically expressed by using a four-dimensional function BRDF (Θi, φi, θr, φr) expressed as the ratio between a ray of incident light source from random direction on a hemisphere and that of reflected energy to random direction. If the reflection characteristics of an object are measured based on the BRDF in a unit of 5 degree, 1,679,616 times of measurements must be performed (1,679,616={90/5*360/5}2). That is, although a unit angle is reduced to ½, the number of measurements increases to 16 times.
However, by using a region based image sensing apparatus the result of detailed measurements less than 5 degree can be obtained according to the resolution of the sensing apparatus. If the region based apparatus is used, we can take accurate measurement without degrading precision of reflection characteristics calculation by controlling the number of measurement times based on a general theory and the characteristics of the apparatus.
Conventionally, the reflection characteristics of an object can be calculated by measuring reflective energy from all directions using an optical mirror or an optical lens. However, that method does not fully consider various spectrum characteristics and diverse geometric characteristics of a target object's surface, such as a scratch or a curve, cannot be accurately reflected on a photorealistic image.
Furthermore, the surface characteristics of an object are reproduced by using a texture map in another conventional technology. However, there is a limitation to reproduce images about all reflected type of the object because of insufficient information about the general reflection characteristics of the object's surface.
It is, therefore, an object of the present invention to provide a system for representing images of a real object and a method thereof. The system uses their photographic images to extract the characteristics of a target object and generates the photorealistic images based on the extracted characteristics
In accordance with an aspect of the present invention, there is provided a system for image representation of an object using photographs, the system including: a characterization unit of an image sensing device for extracting the characteristics of the image sensing device to obtain photographs of a target object; a characterization unit of an object for extracting optical characteristics of the object such as reflectivity and smoothness and so on by analyzing the photographs of the target object acquired by the image sensing device; and an image reproduction unit for reproducing photorealistic images to be suitable to the conditions of expressing the target object by reinterpreting its extracted characteristics.
In accordance with another aspect of the present invention, there is provided a method for image representation of an object by using photographs, the method including the steps of: a) extracting the characteristics of the image sensing device to obtain the photographs of the target object; b) extracting the characteristics of the target object by analyzing the photographs based on the extracted characteristics of the image sensing device and the obtained environment information; and c) reproducing photorealistic images to be suitable to new representation environments according to the extracted characteristics of the object.
The above and other objects and features of the present invention will become better understood with regard to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
Hereinafter, a system for representing an image of a real object by using their photographic images and a method thereof will be described in more detail with reference to the accompanying drawings.
As shown in
Hereinafter, the system for image representation of an object according to the present invention will be explained in detail.
That is, the system for image representation of an object according to the present embodiment includes: a standard illuminant 100 for lighting up an object, a standard optical measurement device 200 which is a reference for optical measurement; a standard object 210 having a well-known reflective rate and standard color; an image sensing device 300 and an exposure controlling device 310 for obtaining photographs of a target object; an extraction device for device characteristics 410 supplementarily provided to extract standardized device characteristics; a extraction module for device characteristics 400 for extracting the characteristics of the device; an extraction device for object characteristics 510 supplementarily provided to extract standardized object characteristics; an extraction module for object characteristics 500 for extracting the characteristics of the target object; an target object 600 which is reproduced; a 3D data 610 which is three-dimensional data of the target object; and a display device 700 and an image reproduction module 800 for displaying reproduced images.
As shown in
In the step S201, the characteristics of the image sensing device 300 are extracted by identifying the location of the standard optical measurement device 200 with that of the image sensing device 300 for providing identical condition to next measurements.
In the step S202, the standard illuminant 100 and the image sensing device 300 are arranged with a defined formation for extracting characteristics of an object based on the photographs of the object.
Also, in the step S203, the display device 700 can be controlled to display images to be closed to be seen by human eyes.
As shown in
Hereinafter, operations of the system for image representation of an object according to the present embodiment will be explained in detail with reference to FIGS. 4 to 9.
Referring to
After setting the test condition, the standard object is measured by using the standard optical measurement device 400 in order to define a reference at step S402, and photographs of the standard object are obtained by the image sensing device at step S403. After obtaining photographs, the characteristics of the image sensing device 300 is obtained by analyzing the obtained photographs and performing the characterization of the image sensing device to minimize difference between output data of the image sensing device 300 and the simulation result for a model of image sensing device at step S404.
Therefore, the characterization unit of an image sensing device 10 extracts and uses the characteristics of the device obtaining region based data by comparing with a conventional standard device obtaining point based data having well-known optical characteristics. Accordingly, the characterization unit of an image sensing device 10 according to the present invention can efficiently acquire data, can be implemented to a conventional R G B system, can be expanded to a wider channel by obtaining much more data, and can accurately compute a bi-directional reflectance distribution function (BRDF) value by using multi-spectral information.
The most general model of an image sensing device is shown in below Eq. 1.
In Eq. 1, the characteristics of the image sensing device is modeled as a si(λ). That is, si(λ) is found by minimizing a difference between a result value ti of the image sensing device 300 and a simulation result of the model
Accordingly, a gamma correction is performed for the simulation result to have non-linearity at step S501. Spectral radiances L(λ) of the standard object are calculated per wavelengths by using a reflective rate r(λ) between the light source L(λ) and the standard object at step S502. In order to minimize the difference, the spectral sensitivity si(λ) of the image sensing device is calculated at step S503.
As shown in
After setting the test environment, photographs of the target object are obtained by using the image sensing device 300 at step S602. During obtaining the photographs, the exposure controlling device 310 is used for controlling an exposure speed of the image sensing device 300 for effectively obtaining necessary data.
After obtaining the photographs, the BRDF value of the target object is calculated, and the photographs are analyzed to form map data by separating images to diffuse reflection and specular reflection at step S603. The characteristics database of the object is built to store the information of the interpreted results which is formed from the extracted characteristics of the object at step S604. The characteristics database may store BRDF data values without modification or the parameters of a selected BRDF model such as Phong, Blinn, Torrance-Sparrow similar to the characteristics of the object.
As shown in
In case of general R G B system, R G B reflectivity (rr,rg,rb) can be calculated by dividing an output value ti of the image sensing device 300 by the calculated illuminant value based on a device spectral sensitivity.
As shown in
After setting, object characteristics information is extracted and reinterpreted to be suitable to the new environment at step S802, and the object is reproduced at step S803. In order to know the difference between a simulation result of the target object and a result obtained from the image sensing device 300, the results are compared at step S804.
As shown in
Then, a corresponding texture map is extracted at step S904, and an object is reproduced according to general graphic rendering process at step S905.
As additional processes, the display device may be set to display the images of the object to be close to be seen by human eyes. That is, the display device is characterized at step S906 and the images to be compared are transformed to a standard CIE coordinate at step 907, and errors (ΔE*ab) of the images within the standard CIE coordinate are calculated at step S908.
The above described method according to the present invention can be embodied as a program and stored on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by the computer system. The computer readable recording medium includes a read-only memory (ROM), a random-access memory (RAM), a CD-ROM, a floppy disk, a hard disk and an optical magnetic disk.
As described above, in the present invention, data of a predetermined area are processed at once by obtaining original data. Therefore, data can be quickly processed in the present invention compared to a conventional point based optical device. Also, by using standardized measurement equipment, test errors can be reduced in the present invention. Furthermore, by obtaining a constant reflectivity according to a light source, synthesis images identical to a real object can be generated based on characteristics of new provided light source.
Accordingly, the system for image representation of an image according to the present invention can generate photorealistic images similar to a real target object although a bad luminance condition for photographing is provided and the target object is located at a bad environment for photographing. Therefore, the system for image representation of an image can be used for producing a movie or a commercial film requiring a realistic reproducing.
The present invention contains subject matter related to Korean patent application No. KR 2004-0093712, filed in the Korean patent office on Nov. 16, 2004, the entire contents of which being incorporated herein by reference.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
Number | Date | Country | Kind |
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10-2004-0093712 | Nov 2004 | KR | national |