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摘要
We qualitatively examine the properties of artificial deformation in the shapes of objects (galaxies, and stars) induced by pixelization effects (also called aliasing effects) using toy mock Simulation images. Two causes of these effects have been recognized. One is a consequence of observing the continuous sky with discrete pixels, which is called "first pixelization". The other, called "second pixelization", is a consequence of resampling a pixelized image onto another pixel grid whose coordinates are not perfectly adjusted to the input grid. We pay special attention to the latter, because it might be a potential source of a systematic noise in weak-lensing analysis. In particular, it is found that resampling with rotation induces artificial ellipticities in object shapes having a periodic concentric-circle-shaped pattern. Our major findings are as follows: (1) The root-mean-square (RMS) of artificial ellipticities in object shapes induced by the first pixelization effect can be as large as RMS greater than or similar to 10(-2) if the characteristic size of the objects (e.g., the FWHM) is smaller than twice of the pixel size. However, for larger objects, it quickly becomes very small (RMS less than or similar to 10(-5)). (2) The amplitude of shape deformation induced by the second pixelization effect depends on the object size. It also depends strongly on the interpolation scheme adopted to carry out resampling and on the grid size of the output pixels. The RMS of ellipticities in object shapes induced by the second pixelization effect can be suppressed to well below 10(-2) if one adopts a proper interpolation scheme (implemented in Popular image processing softwares). We also discuss the impact of pixelization effects an a weak-lensing analysis.
- 出版日期2008
- 单位中国科学院国家天文台
