Abstract

We propose an image-resolution upscaling method for compact imaging systems. The image resolution is calculated using the resolving power of the optics and the pixel size of a digital image sensor. The resolution limit of the compact imaging system comes from its size and the number of allowed lenses. To upscale the image resolution but maintain the small size, we apply wavefront coding and image restoration. Conventional image restoration could not enhance the image resolution of the sensor. Here, we use the upscaled image of a wavefront-coded optical system and apply an image-restoration algorithm using a more precisely calculated point-spread function (PSF) as the deconvolution filter. An example of a wavefront-coded optical system with a 5-megapixel image sensor is given. The final image had a resolution equivalent to that of a 10-megapixel image using only four plastic lenses. Moreover, image degradation caused by hand motion could also be reduced using the proposed method.

© 2010 Optical Society of America

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References

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  1. S. S. Reddi, “Constrained least-squares image restoration: an improved computational scheme,” Appl. Opt. 17, 2340–2341 (1978).
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  5. S.-H. Lee, N.-C. Park, and Y.-P. Park, “Breaking diffraction limit of a small f-number compact camera using wavefront coding,” Opt. Express 16, 13569–13578 (2008).
    [CrossRef] [PubMed]
  6. R. C. Gonzalez and R. E. Woods, Digital Image Processing (Prentice Hall, 2002), Chap. 5.
  7. International Standard ISO 12233:2000.
  8. MIL-STD-150A Military Standard Photographic Lenses.

2008 (1)

2003 (1)

2002 (2)

W. T. Cathey and E. R. Dowski, “New paradigm for imaging systems,” Appl. Opt. 41, 6080–6092 (2002).
[CrossRef] [PubMed]

R. C. Gonzalez and R. E. Woods, Digital Image Processing (Prentice Hall, 2002), Chap. 5.

1995 (1)

1978 (1)

Cathey, W. T.

Dowski, E. R.

Gonzalez, R. C.

R. C. Gonzalez and R. E. Woods, Digital Image Processing (Prentice Hall, 2002), Chap. 5.

Kubala, K.

Lee, S.-H.

Park, N.-C.

Park, Y.-P.

Reddi, S. S.

Woods, R. E.

R. C. Gonzalez and R. E. Woods, Digital Image Processing (Prentice Hall, 2002), Chap. 5.

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Figures (15)

Fig. 1
Fig. 1

Wavefront coding and image upscaling process. (a) Schematic diagram, and (b) flow chart.

Fig. 2
Fig. 2

(a) Initial lens design, (b) wavefront aberration of conventional lens design, and (c) PSFs of conventional lens design.

Fig. 3
Fig. 3

(a) Wavefront-coded lens design, (b) wavefront aberration of wavefront-coded lens design, and (c) PSFs of wavefront-coded lens design.

Fig. 4
Fig. 4

Original PSF of wavefront-coded lens design.

Fig. 5
Fig. 5

PSFs as deconvolution filters (a) for the 5 -megapixel image, (b) for the resized 10 -megapixel image, and (c) for the resized 20 -megapixel image.

Fig. 6
Fig. 6

(a) ISO 12233 and (b) USAF 1591 resolution charts.

Fig. 7
Fig. 7

Restored images: (a) 5 -megapixel image from the ISO 12233 resolution chart, (b) 5 -megapixel image from the USAF 1591 resolution charts, (c), (d) upscaled and restored 10 -megapixel image using a recalculated deconvolution filter [Fig. 5b], (e), (f) upscaled and restored 20 -megapixel image using a recalculated deconvolution filter (Fig. 5c).

Fig. 8
Fig. 8

Spatial frequency response of (a) a restored 5 -megapixel image, (b) an upscaled and restored 10 -megapixel image, and (c) an upscaled and restored 20 -megapixel image.

Fig. 9
Fig. 9

Restored 20 -megapixel images and SFRs using the deconvolution filters that are weighted sums of PSFs.

Fig. 10
Fig. 10

(a) Lens movement from side to side due to hand motion, and (b) image blurred by hand motion.

Fig. 11
Fig. 11

5 -Megapixel image restored using a deconvolution filter [Fig. 5a].

Fig. 12
Fig. 12

Upscaled ( 10 -megapixel ) and restored image using a recalculated deconvolution filter [Fig. 5b].

Fig. 13
Fig. 13

Upscaled ( 20 -megapixel ) and restored image using a recalculated deconvolution filter [Fig. 5c].

Fig. 14
Fig. 14

Spatial frequency response of (a) a restored 5 -megapixel image, (b) an upscaled and restored 10 -megapixel image, and (c) an upscaled and restored 20 -megapixel image from the hand-motion-blurred image.

Fig. 15
Fig. 15

(a) Hand-motion-blurred image of Tower Bridge and (b) an upscaled and restored image.

Tables (1)

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Table 1 Specifications of the Wavefront-Coded Optical System

Equations (2)

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F ̂ ( u , v ) = [ H * ( u , v ) | H ( u , v ) | 2 + γ | P ( u , v ) | 2 ] G ( u , v ) ,
P = ( 0 1 0 1 4 1 0 1 0 ) .

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