Johji Tajima

3-D data acquisition by Rainbow Range Finder

The Rainbow Range Finder (RRF) has the ability to obtain range information for all image pixels with only one frame TV camera imaging during 1/30 s. The authors propose a novel practical calibration scheme which makes range measurement for all visible pixels possible. An experimental system was developed on that basis, and measurement accuracy was evaluated. A curved surface and a plain surface could be measured with sufficient accuracy. The feasibility of a real-time system with an accuracy of 1% in regard to the measurement region size was demonstrated.<<ETX>>

Uniform color scale applications to computer graphics

People who are engaged with computerized image processing are often worried by computer-processed results that were not anticipated. These results often occur in color displayed images. The reason is that the color difference measured in red, green, and blue (RGB) space is not perceived linearly by human eyes. The uniform color scale is adopted as an approximation to the human visual system, On this basis, data conversions are proposed that enable the matching of computer image processing to human sensing. A pseudo-color selection method and optimal color TV display characteristics are also derived from the conversion formula between the RGB and Uniform Color Scale spaces.

Absolute phase measurements using geometric constraints between multiple cameras and projectors.

The method of phase shift with the projection of multiple cyclic patterns enables 3D measurement that is highly accurate, dense, and fast. However, this measurement is only possible for the wrapped phase value, which has ambiguities in its multiples of cycles. Two particular problems are that conventional methods require additional patterns to be projected to determine the absolute phase and that unwrapping the phase tends to fail where depth varies abruptly. Two methods are proposed: the first is to determine the absolute phase without additional patterns being projected by observing the projected pattern with multiple cameras and applying the geometric constraints between them, and the second is to prevent failure in unwrapping the phase by referring to continuities in the relative phases of multiple projected patterns. The proposed methods were achieved with a 3D scanner that can measure approximately a 180 degrees field of view within 0.5 s, with an accuracy of 0.14 mm in depth.

Content-Adaptive Automatic Image Sharpening

Optimal sharpness differs from image to image, de-pending on the content. In general, human observer prefers images of artifacts sharper and those of natural-objects less sharper. We have developed a content-adaptive automatic image sharpening algorithm that relies on the length of lines extracted from the image. It is applicable to images with various regions such as those contain natural and artificial objects. The proposed algorithm is expected to be used in image processing modules of image input/output devices, e.g. digital cameras, printers, etc.

Color matching algorithm based on computational 'color constancy' theory

This paper describes a new color appearance matching method based on color constancy theory. In order to achieve good color appearance matching between different color devices such as a CRT-monitor and a printer, whose whites are quite different, the method recovers the hypothetical surface reflectances of objects and the hypothetical spectral power distribution of the illumination in a scene. The hypothetical surface reflectances are changed in accordance with illumination changes and used to calculate corresponding colors under a target illumination. Our method requires no complicated calculation and gives good color appearance matching. Experiments have confirmed the validity of the proposed algorithm.

A Multiple-baseline Stereo for Precise Human Face Acquisition

Abstract Stereo algorithms can provide useful three-dimensional information for a variety of purposes, including face recognition. For good accuracy, the distance between cameras should be large. However, the large baseline often makes the correspondence problem more difficult. In this paper, we examine the problem of non-Lambertian reflectivity in multi-baseline stereo and propose a refined multiple-baseline stereo technique which estimates the brightness on each camera by using adjacent cameras. In this way, the erroneous stereo correspondences due to brightness changes caused by non-Lambertian reflectance can be reduced without needing to explicitly model the actual reflectance model. Experimental results are presented and significant reductions in correspondences errors are demonstrated in comparison with previous methods.

Illumination Chromaticity Estimation Based on Dichromatic Reflection Model and Imperfect Segmentation

The illumination chromaticity estimation based on the dichromatic reflection model has not been made practicable, since the method needs image segmentation beforehand. However, its two-dimensional model is sufficiently robust, when it is combined with the least square method. The proposed algorithm executes the color space division instead of the segmentation. The original image is divided into small color regions, each of which corresponds to one of color sub-spaces. Though this division is imperfect image segmentation, the illumination chromaticity estimation based on the chromaticity distribution in the color regions is possible. Experimental result shows that this method is also applicable to images of apparently matt surfaces.

Selective color correction for arbitrary hues

This paper proposes new selective color correction methods for digital color images, which do not require masking of the correction area. The most commonly employed method can only effectively correct pixels containing one of six specific hues (R.G.B.C.M.Y). In response to this situation, the authors have developed two new selective color correction methods, the HSV method and the RGB subtractive method, both of which can be applied to arbitrary hues within a adjustable hue range. In actual testing, the methods have produced excellent results, and may be expected to make it easier for users to retouch photograph images.

Consideration and experiments on object spectral reflectance for color sensor evaluation/calibration

The influence of existing spectral reflectances and sensor sensitivities on color reproduction duality is studied. We analyzed the distribution of 17 categories of object spectral reflectance, using the standard object colour spectra database for colour reproduction evaluation (SOCS). Then we evaluated the color reproduction quality of sensors for each category wing SOCS and five sample sensor sensitivity, allowing linear color correction as a post-processing to sensor outputs. We obtained the following results: 1) spectral reflectance restoration quality is closely related to the subspace dimensions that the spectral reflectances span; 2) the rank of sensor-set color reproduction quality is mostly stable and not greatly affected by the object categories; and 3) if one choose a category of artificial object colors for linear correction parameter calibration, the parameters may be applied to other categories of such object. These findings suggest that the color reproduction quality of sensors can be estimated using some standardized spectral reflectance data sets.

Color scheme supporting method in a color design system

This paper describes a new method for assisting the coloring work to achieve good color harmony in documents that contain color diagrams, figures, or images. Generally, good quality for a color document is achieved by color-element unification. Tone, a color element, is often used to arrange color harmony in a color document. A tone model is proposed that describes the color harmonization concept. An approximation formula is developed to describe the tone model. It enables simple correspondence between color coordinates and their tones. Using the tone model, users can generate a color palette that consists of colors whose subjective impression is unified. This palette is provided for coloring work, Because each of these colors has a uniform element in common, a color document, which is painted by colors from one palette, achieves the color harmonization. The tone model also provides another kind of human interface that allows the users to intuitively select a color by using the adjectives that give us the impression of color variations. Emphasis on a diagram part by selecting a color with a different tone is easily visualized. Using the prototype system, the time for coloring work was significantly reduced.