The modeling and the optimization of a grating optical low-pass filter

Go, Chun-Soo; Lim, Sungwoo; Kim, S.; Lee, J.-C.; Oh, Yong-Ho

doi:10.1007/s003400100678

Cited by 8 publications

(7 citation statements)

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“…For the natural images captured using the camera, the proposed moiré reduction method was compared with previous methods [5], [12]. Figures 14 (a) For the visual comparison, the moiré regions are magnified in (b), (d), (g), and (j) of Figs.…”

Section: Resultsmentioning

confidence: 99%

“…However, conventional digital cameras use more than two OLPFs with different orientations that are stacked and assembled with separate optical lenses, which induces blurring in the captured image and increases the manufacturing cost. Thus, for mobile devices, a grating optical low pass filter (GOLF) with a thin plate of phase grating is used to decrease the number of lens elements [5], [6]. Consequently, high-frequency aliasing is removed using an OLPF or GOLF.…”

Section: Introductionmentioning

confidence: 99%

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Moiré Reduction Using Inflection Point and Color Variation in Digital Camera of No Optical Low Pass Filter

Kim

Kyung

et al. 2015

IEICE Trans. Inf. & Syst.

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SUMMARYThe role of an optical low-pass filter (OLPF) in a digital still camera is to remove the high spatial frequencies that cause aliasing, thereby enhancing the image quality. However, this also causes some loss of detail. Yet, when an image is captured without the OLPF, moiré generally appears in the high spatial frequency region of the image. Accordingly, this paper presents a moiré reduction method that allows omission of the OLPF. Since most digital still cameras use a CCD or a CMOS with a Bayer pattern, moiré patterns and color artifacts are simultaneously induced by aliasing at high spatial frequencies. Therefore, in this study, moiré reduction is performed in both the luminance channel to remove the moiré patterns and the color channel to reduce color smearing. To detect the moiré patterns, the spatial frequency response (SFR) of the camera is first analyzed. The moiré regions are identified using patterns related to the SFR of the camera and then analyzed in the frequency domain. The moiré patterns are reduced by removing their frequency components, represented by the inflection point between the high-frequency and DC components in the moiré region. To reduce the color smearing, color changing regions are detected using the color variation ratios for the RGB channels and then corrected by multiplying with the average surrounding colors. Experiments confirm that the proposed method is able to reduce the moiré in both the luminance and color channels, while also preserving the detail. key words: optical low pass filter, moiré reduction, color smearing, image quality

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Moiré Reduction Using Inflection Point and Color Variation in Digital Camera of No Optical Low Pass Filter

Kim

Kyung

et al. 2015

IEICE Trans. Inf. & Syst.

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“…Fig.7 (a) is the original z resolution is 768 460 with pixe Fig.7(b) and (c) are the resulting im activating birefringence of the lense fringes are those circles located awa Compared to the original image, the significantly suppressed in Fig.7(b fringes are still detectable around lef moire fringes were further su birefringence of the lenses, which ca However, the circles located at the im moire fringes, were also blurred by ray separation is long at low field results in Table II and III. To overcom should not be too long at low field an It has been reported that an ideal O higher frequency components than the image sensor while pass a components [2] [3]. This is also true system.…”

Section: Evaluation Andmentioning

confidence: 97%

Ultra-small imaging system for cell phone camera using birefringent lenses

Zhang

Ueda

2011

2011 IEEE SENSORS Proceedings

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In this research, an ultra-small ima birefringent lenses was presented. This syste the next generation mobile phone camera wit of smaller pixel size. The system thickne approximately 1.7mm (from the first lens' fr image sensor) by employing one aspheric lens lens made of birefringent uniaxial crystal, wh optical low pass filters (OLPFs). In conve however, the OLPFs are stacked up and ass with optical lenses, which makes it difficult thickness. Quantitative and visual results of or ordinary ray separation on the image plane d the birefringent lenses system is able to cut of frequencies than the Nyquist frequency of image sensor.I.

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“…To calculate the diffraction pattern, the material from which the GOLF is made must be lossless within the range of the working wavelength. According to the Fresnel-Kirchhoff theory, the light intensity I(x) at the CCD plate can be calculated as follows [6]:…”

Section: Theoretical Basis Of Golfmentioning

confidence: 99%

“…Generally, the GOLFs have been fabricated by the semiconductor lithographic process [4][5][6]. However, this process is too complicated and expensive for massproduction.…”

Section: Fabrication Of the Golfmentioning

confidence: 99%

Making optical low-pass spatial filters by thin-film phase grating

Chen

Zou

Lee

2006

Journal of Modern Optics

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A modified rule was applied to design a grating optical low-pass spatial filter (GOLF) with a thin-film phase grating. This filter differed from the crystal type of optical low-pass spatial filter (OLPF). The fabrication method of the thin-film phase GOLF was also different from the conventional lithographic process. A new fabrication method utilizing a metal mesh mask and a thin-film coating process was applied to make the GOLF. The process had the advantages of being simple and cheap, and would thus be good for mass-production. The modulation transfer function (MTF) of the device was measured and the results agree well with the theoretical calculations. Finally, the GOLF was installed on a digital camera which was used to capture images of the circular zone plane (CZP), to show the Moire´pattern suppression ability.

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The modeling and the optimization of a grating optical low-pass filter

Cited by 8 publications

References 0 publications

Moiré Reduction Using Inflection Point and Color Variation in Digital Camera of No Optical Low Pass Filter

Moiré Reduction Using Inflection Point and Color Variation in Digital Camera of No Optical Low Pass Filter

Ultra-small imaging system for cell phone camera using birefringent lenses

Making optical low-pass spatial filters by thin-film phase grating

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