Ryuji Matsuoka

Comparison of Image Interpolation Methods Applied to Least Squares Matching

Least squares matching requires appropriate interpolation of the gray values in the search window corresponding to a template. This paper reports an experiment conducted to evaluate image interpolation methods on matching accuracy of least squares matching by using 54 diverse images. Three popular methods in photogrammetry: bilinear interpolation [BL], cubic convolution by Riffman [C1], and cubic convolution by Simon [C2] were investigated. The results demonstrate that [C2] can produce better matching results than [BL] and [C1] in most cases when an image has no noise or smaller noises. Meanwhile, the results demonstrate that there is nothing to choose among three interpolation methods when an image has larger noises. Since the differences of the matching accuracy among three methods were small enough to be neglected, we conclude that [BL] would be the best interpolation method applied to least squares matching in most cases considering its inexpensive computational cost.

Measurement accuracy of center location of a circle by centroid method

This paper reports an investigation of the effect of digitization on the measurement accuracy of the center location of a circle by a centroid method. Although general expressions representing the measurement accuracy of the center location of a circle by the centroid method are unable to be obtained analytically, we have succeeded in obtaining the variances V of measurement errors for 39 quantization bits n ranging from one to infinity by numerical integration. We have succeeded in obtaining the effective approximation formulae of V as a function of the diameter d of the circle for any n as well. The results show that V would oscillate on an approximate one-pixel cycle in d for any n and decrease as n increases. The differences of V among the different n would be negligible when n ≥ 6. Some behaviors of V with an increase in n are demonstrated.

Calibration of low-cost measurement system by using a consumer digital stereo camera

The consumer digital stereo camera FinePix REAL 3D W1, which was designed to take a pair of stereo images for stereo viewing, was released in August 2009. The aim of our study is to evaluate camera calibration methods for a low-cost and easy-operation system to measure dimensions of an object on a sub-meter scale only by using a pair of stereo images acquired by the camera without any controls such as control points whose spatial locations are known or a ruler which provides the scale of the object. Three camera calibration methods were evaluated by estimation errors of lengths of line segments measured without any controls. The experiment results indicate that the best calibration method would be the method that ordinary camera calibration is first executed for each imaging unit in order to estimate its image distortion model, and then alignment between two imaging units is estimated by using two sets of the exterior orientation parameters of both imaging units obtained in the ordinary camera calibration executed previously. The experiment results indicate that the suitable calibration method would be able to provide sufficiently accurate measurement results less than 0.4 pixels on an image as well.

Comparison on accuracy of image matching between lossy JPEG compression and lossy JPEG 2000 compression

This paper reports an experiment conducted in order to compare lossy JPEG compression and lossy JPEG 2000 compression on the accuracy of image matching. The experiment has been conducted by using 54 color images of diverse textures and diverse tones of color on the assumption that image matching utilizes a pair of images reconstructed from image data which are lossily compressed in an ordinary digital camera. Lossy JPEG compression has been executed with a set of compression parameters utilized in a digital camera Canon EOS 20D, while lossy JPEG 2000 compression has been executed in the way as the file size of a piece of JPEG 2000 compressed image data is the same file size of the corresponding JPEG compressed image data. Moreover, we have prepared another set of JPEG and JPEG 2000 compressed image data which are lossily compressed with the compression ratio expected for an ordinary color image when it is compressed in the EOS 20D. When the file size of a piece of JPEG 2000 compressed image data is the same as that of a piece of JPEG compressed image data, the experiment results clearly show that the compression performance of JPEG 2000 compression would be superior to that of JPEG compression on image quality as to pixel value in RGB color space. On the contrary, the results do not necessarily indicate that JPEG 2000 compression would be able to provide more accurate matching results than JPEG compression.

Terrain elevation measurement from ALOS/PRISM stereographic images

12 PRISM, a panchromatic stereomatic sensor with 2.5m resolution, is planned to be launched in 2003. Because observing data rate of PRISM is very high, lossy data compression will be applied on the board satellite in order to decrease the downlink data rate to ground receiving stations. The object of this study is to evaluate influences of the lossy data compression, atmospheric effects and S/N of the sensor for terrain elevation measurement. As the results, the following conclusions were given. Firstly, low S/N increases mean elevation error under the restriction that forward/backward viewing vectors converge within two pixels. Secondly, data compression and turbid atmosphere decrease the mean elevation error, preferably. Thirdly, data compression ratio of 1/6 is recommended in practical operation of PRISM. In this case, mean elevation error less than or equal to 3m can be achieved without relation of atmospheric condition and S/N.

A Study on Change Monitoring of the Huanghe Dalta using LANDSAT Imagery

黄河は世界でも有数の土砂の多い河川であり, 大量の土砂流出による三角州を形成してきた。その量は年平均10～12億トンに達するといわれ, 平均して年に150～400mずつ三角州が海に張り出し, その面積は100年くらいで約23km2/年の割り合で増加してきたという。しかし, 大躍進時間 (1958～1960) および文化大革命時 (1966～1976) に上流部で森林を乱伐した影響もあり, 最近の20年間は約40km2/年の割合で三角州の発達が倍加しているといわれる。黄河河口は油田地帯でもあり, それに伴なう港湾施設の建設および管理を行う必要から, 三角州の発達を追跡し, さらにその将来予測することはきわめて重要である。本研究はLANDSAT画像による黄河三角州の変化追跡の有効性をいくつかの事例研究をもとに明らかにしたものである。