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Accurate color image reproduction under arbitrary illumination can be realized if the spectral reflectance functions in a scene are obtained. Although multispectral imaging is one of the promising methods to obtain the reflectance of a scene, it is expected to reduce the number of color channels without significant loss of accuracy. This paper presents what we believe to be a new method for estimating spectral reflectance functions from color image and multipoint spectral measurements based on maximum a posteriori (MAP) estimation. Multipoint spectral measurements are utilized as auxiliary information to improve the accuracy of spectral reflectance estimated from image data. Through simulations, it is confirmed that the proposed method improves the estimation accuracy, particularly when a scene includes subjects that belong to various categories.

Nonlinear estimation method of spectral reflectance from camera responses is proposed. The proposed method minimizes the mean square error of spectral reflectance when the reflectance can be regarded as a random sequence of Gaussian mixture distribution. In computer simulations, 168 samples of spectral reflectance from a color chart are estimated from their image signals obtained by three- and six-band cameras. It is confirmed that the proposed method improves the accuracy in comparison with the conventional Wiener estimation method.

We propose a high-speed surface reconstruction from three-dimensional data through optical–digital hybrid processing. Surface images are currently reconstructed through digital processing, which takes a long time mainly because of the rotation and interpolation of the volume data. In the proposed system, slice images of three-dimensional volume data are optically rotated and interpolated. In principle, one surface image can be obtained in the video rate when we use the same number of sets of optical processors as slices to be processed. Furthermore, this system could lead to a hybrid three-dimensional simulator; most operations such as rotation, cutting, digging holes, and peeling skins are interactively achieved at the video speed. Fundamental experiments are described that confirm the effectiveness of this method.

An advanced coded imaging system is described, and some results of phantom experiments are presented. The advanced method uses a pair of coherent codes (+ 1 and -1 codes) and has many advantages compared with conventional ones. One of the greatest advantages is that there are no sidelobes in the focal plane and only a few in other planes. Therefore, when an object can be regarded as two-dimensional, it is perfectly reconstructed with high detecting efficiency, and this is successfully simulated by a thyroid phantom with 99mTc. Moreover, this system has an ability to reconstruct tomograms, which is also shown by using ring phantoms piled on one another with some cold spots in their shells. From these experimental results it may be concluded that the new system is useful for practical applications, for example, to nuclear medicine.

Color CCD endoscopes with sequential three-color illuminations have the advantage of high spatial resolution but are sensitive to object motion. A digital method is proposed for the restoration of images color-shifted by the object motion. The method makes use of phase-only matching followed by a resampling operation to compensate for a space-variant shift between different primary color images. Restored images are suitable for further image processing such as color emphasis and structure enhancement.

Simulated annealing, a Monte Carlo-like algorithm, is applied to three-dimensional blood vessel reconstruction based on digital subtraction angiography. Since imaging systems often employ an insufficient number of projections, adequate reconstruction from observed data is not possible. It is shown that even in such cases objects can be sufficiently reconstructed by simulated annealing, which makes use of constraints based on a priori knowledge. This method is successfully demonstrated with a fundamental computer simulation.