-
▶ 출처
모든 투명한 물체들(예를들어 렌즈)의 각 파장에 대한 굴절율이 다르기 때문에, 모든 all three primary colors (i.e., red, green and blue)를 어떤 광학적 보정없이 같은 위치에 도달하게 할 수가 없다.
두 가지 컬러에 대해서 보정을 하고 하나의 위치로 모아주는 렌즈를 achromatic이라고 하고, 모든 세가지 컬러에 대해서 보정하고 하나로 모으는 렌즈를 apochromatic라고 한다.
만일 세개의 컬러에 대해서 같은 위치로 옮겨주는 일을 하지 않는 렌즈는 색수차(chromatic aberration)가 발생하게 된다. 즉, 그런 렌즈로 인해서 물체 경계부근에 실제 scene에는 존재하지 않는 색이 나타나게 된다.
DSC경우에는 CCD나 CIS 같은 image capturing device들도 색수차에 어느정도 기여(?)를 한다.
센서의 각 픽셀들이 모두 촘촘하게 붙어있기 때문에, 한 픽셀에 capture되는 색들이 주위의 다른 픽셀들에 영향을 줄 수가 있고, 이는 색수차와 유사한 현상이 발생한다.
아래 그림들의 노란색 상자들은 색수차 현상들을 보여주고 있다.
--------------------------------------------------------------------------------------------------▶ 위키피디아 내용 (번역할까 했으나 귀찮고, 위에 이미 간단한 설명이 있으니 필요없음 ㅋ)
In optics, chromatic aberration (also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength.
Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point on the optical axis.
Since the focal length f of a lens is dependent on the refractive index n, different wavelengths of light will be focused on different positions. Chromatic aberration can be both longitudinal, in that different wavelengths are focused at a different distance from the lens; and transverse or lateral, in that different wavelengths are focused at different positions in the focal plane (because the magnification of the lens also varies with wavelength).
The term "purple fringing" is commonly used in photography, although not all purple fringing can be attributed to chromatic aberration. Similar colored fringing around highlights may also be caused by lens flare. Colored fringing around highlights or dark regions may be due to the receptors[clarification needed] for different colors having differing dynamic range or sensitivity -- therefore preserving detail in one or two color channels, while "blowing out" or failing to register, in the other channel or channels. On digital cameras, the particular demosaicing algorithm is likely to affect the apparent degree of this problem. Another cause of this fringing is chromatic aberration in the very small microlenses used to collect more light for each CCD pixel; since these lenses are tuned to correctly focus green light, the incorrect focusing of red and blue results in purple fringing around highlights. This is a uniform problem across the frame, and is more of a problem in CCD's with a very small pixel pitch such as those used in compact cameras. Some cameras, such as the Panasonic Lumix series and newer Nikon DSLRs, feature a processing step specifically designed to remove it.
On photographs taken using a digital camera, very small highlights may frequently appear to have chromatic aberration where in fact the effect is because the highlight image is too small to stimulate all three color pixels, and so is recorded with an incorrect color. This may not occur with all types of digital camera sensor. Again, the demosaicing algorithm may affect the apparent degree of the problem.
[edit]Black-and-white photographyChromatic aberration also affects black and white photography. Although there are no colors in the photograph, chromatic aberration will blur the image. It can be reduced by using a narrow-band color filter, or by converting a single color channel to black and white. This will, however, require longer exposure. (This of course is only true with panchromatic black and white film, since orthochromaticfilm is already sensitive to only a limited spectrum.)
'Colour|Image > Image_Sensor' 카테고리의 다른 글
Active Pixel Sensor (0) 2009.08.04 FinePix REAL 3D Technology Debut (0) 2009.07.27 Time-of-Flight camera (0) 2009.06.03 댓글
