Study on Distortion Compensation of Underwater Archaeological Images
 Acquired through a Fisheye Lens and Practical Suggestions for Underwater
 Photography
 - A Case of Taean Mado Shipwreck No. 1 and No. 2 -

Underwater archaeology relies heavily on photography and video image recording during surveillances and excavations like ordinary archaeological studies on land. All underwater images suffer poor image quality and distortions due to poor visibility, low contrast and blur, caused by differences in refractive indices of water and air, properties of selected lenses and shapes of viewports. In the Yellow Sea (between mainland China and the Korean peninsula), the visibility underwater is far less than 1 m, typically in the range of 30 cm to 50 cm, on even a clear day, due to very high turbidity. For photographing 1 m x 1 m grids underwater, a very wide view angle (180o) fisheye lens with an 8 mm focal length is intentionally used despite unwanted severe barrel-shaped image distortion, even with a dome port camera housing. It is very difficult to map wide underwater archaeological excavation sites by combining severely distorted images. Development of practical compensation methods for distorted underwater images acquired through the fisheye lens is strongly desired. In this study, the source of image distortion in underwater photography is investigated. We have identified the source of image distortion as the mismatching, in optical axis and focal points, between dome port housing and fisheye lens. A practical image distortion compensation method, using customized image processing software, was explored and verified using archived underwater excavation images for effectiveness in underwater archaeological applications. To minimize unusable area due to severe distortion after distortion compensation, practical underwater photography guidelines are suggested.

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A Slotted Electrode Stigmator for Correction of Short Focal Length Objectives

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100061148 ◽

1967 ◽

Vol 25 ◽

pp. 226-227 ◽

Cited By ~ 1

Author(s):

J. H. Reisner ◽

J.J Schuler

Keyword(s):

Focal Plane ◽

Focal Length ◽

Image Distortion ◽

Slot Width ◽

Objective Lens ◽

Physical Restraints ◽

Critical Dimensions ◽

Short Focal Length ◽

Magnetic Poles ◽

Simple Reduction

One of the difficulties which must be overcome in the design of objective lens stigmators is that they necessarily take up space where it is most precious, in the vicinity of the specimen. The space following the specimen is needed for the contrast aperture while the space between magnetic poles in the gap is required for stage mechanism. To go appreciably below the objective back focal plane to position stigmators subjects the image to possible image distortion when correction is large. A further problem is caused by the trend to shorter objective focal lengths, e.g., 1.5 mm, thus further reducing the space available for the stigmator.To adapt the electrostatic stigmator to these physical restraints, a design has been completed which is only 0.75 mm thick and has a free bore diameter of the same size. Its sensitivity is 0.1 micron/volt with 100 kV electrons. The overall diameter is uncritical and may be adapted to the physical requirements of the system. It should be possible to make stigmators of 3 mm thickness with a simple reduction of critical dimensions (thickness and slot width).

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Image Distortion Compensation by Using a Polynomial Model in an X-Ray Digital Tomosynthesis System

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.297-300.2034 ◽

2005 ◽

Vol 297-300 ◽

pp. 2034-2039 ◽

Cited By ~ 1

Author(s):

J.Y. Kim ◽

J.S. Yoon

Keyword(s):

Flip Chip ◽

Image Intensifier ◽

Industrial Applications ◽

Image Distortion ◽

Polynomial Model ◽

Digital Tomosynthesis ◽

Cross Sectional ◽

Distortion Compensation ◽

X Ray ◽

Cross Sectional Imaging

X-ray technology has been widely used in a number of industrial applications for monitoring and inspecting inner defects which can hardly be found by normal vision systems as a ball grid array (BGA) or a flip chip array (FCA). Digital tomosynthesis (DT) is one of the most useful X-ray cross-sectional imaging methods for PCB inspection, and it usually uses an X-ray image intensifier. However, the image intensifier distorts X-ray images severely both of shape and intensity. This distortion breaks the correspondences between those images and prevents us from acquiring accurate cross-section images. Therefore, image distortion compensation is one of the most important issues in realizing a DT system. In this paper, an image distortion compensation method for an X-ray DT system is presented. It is to use a general distortion polynomial model on two dimensional plane that can cope with arbitrary, complex and various forms of distortion. Experimental results show a great improvement in compensation speed and accuracy.

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High-resolution photothermoplastic matrix storage media for low-contrast halftone image recording

10.1117/12.301396 ◽

1998 ◽

Cited By ~ 2

Author(s):

Yuri A. Cherkasov ◽

Yuri M. Chesnokov ◽

Yan L. Ziman ◽

Elena L. Alexandrova ◽

Svetlana P. Yefimova ◽

...

Keyword(s):

High Resolution ◽

Low Contrast ◽

Image Recording ◽

Halftone Image ◽

Storage Media

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A study of distortion correction algorithms based on aspheric fisheye lens design

Optica Applicata ◽

10.37190/oa200406 ◽

2020 ◽

Vol 50 (4) ◽

Author(s):

Dan Li ◽

Baolong Zhang ◽

Jiawei Zhu ◽

Qi Wang ◽

Zhenwei Zhu

Keyword(s):

Design Method ◽

Focal Length ◽

Distortion Correction ◽

Maximum Diameter ◽

Image Point ◽

Modulation Transfer ◽

Fisheye Lens ◽

Corrected Image ◽

Glass Lens ◽

Working Distance

A design method of aspheric fisheye lens has been proposed in this paper, based on the requirements of automobile surround view system. The study has designed a kind of ultra-wide-angle fisheye lens, which only consists of a spherical glass lens and three aspherical plastic lenses. The maximum diameter of imaging aperture is 15.3 mm; the working distance behind is 2.158 mm; the total length of system is 11.44 mm; the focal length is 0.97 mm; the viewing angle is 210°, and the modulation transfer function (MTF) curve is 0.35 at 60 lp/mm. Furthermore, a kind of a distortion correction algorithm for fisheye lens has been created, which calculates the position of the ideal image point with the actual image point and the obtained distortion curve and distortion model. The algorithm can correct the distorted image taken by a fisheye lens to an image without distortion, which is suitable for the human eye. The algorithm, which is simple and effective, has been applied to the automobile surround view system. It has been verified to be accurate and reasonable, after the comparison is made between the real image taken by a fisheye lens and the corrected image.

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Developments in TEM for life-science research

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017030x ◽

1994 ◽

Vol 52 ◽

pp. 514-515

Author(s):

U. Lücken ◽

Wim M. Busing ◽

Michael Felsmann ◽

Frank de Jong ◽

Max T. Otten

Keyword(s):

Life Science ◽

Materials Science ◽

Focal Length ◽

Science Research ◽

Objective Lens ◽

High Contrast ◽

Contrast Imaging ◽

Low Contrast ◽

High Contrast Imaging ◽

Small Spot

The study of Life Science materials with the TEM faces a number of problems such as low contrast in unstained specimens and specimen sensitivity to electron-beam damage and poor vacuum. Providing solutions to these problems has been the basis for several new developments on the Philips CM-series TEMs.Objective lenses traditionally have been optimised for parameters that are important in materials science: high resolution and very small spot sizes. With these parameters comes a short focal length which reduces the contrast from the specimen - no problem in the high-contrast materials science specimens, but highly problematic in the case of low-contrast biological specimens. A new objective lens - the BioTWIN - has been developed specifically for high-contrast imaging and analysis of biological specimens. Its long focal length (6.2 mm; 2 to 3 times larger than that of a typical materials science objective lens) ensures high contrast by enabling the removal of the majority of elastically and inelastically scattered electrons by the objective aperture. Figure 1 shows a comparison of images of a stained section imaged at low magnification, recorded with a TWIN and a BioTWIN lens.

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