Browsing by Subject "Optical resolving power"

Now showing 1 - 5 of 5

Open Access
Adaptive methods for dithering color images
(Institute of Electrical and Electronics Engineers, 1997-07) Akarun, L.; Yardımcı, Y.; Çetin, A. Enis
Most color image printing and display devices do not have the capability of reproducing true color images. A common remedy is the use of dithering techniques that take advantage of the lower sensitivity of the eye to spatial resolution and exchange higher color resolution with lower spatial resolution. In this paper, an adaptive error diffusion method for color images is presented. The error diffusion filter coefficients are updated by a normalized least mean square-type (LMS-type) algorithm to prevent textural contours, color impulses, and color shifts, which are among the most common side effects of the standard dithering algorithms. Another novelty of the new method is its vector character: Previous applications of error diffusion have treated the individual color components of an image separately. Here, we develop a general vector approach and demonstrate through simulation studies that superior results are achieved.
Open Access
Characterization and imaging with lamb wave lens at gigahertz frequencies
(IEEE, 1994-10-11) Bozkurt, Ayhan; Yaralıoğlu, Göksenin; Atalar, Abdullah; Köymen, Hayrettin; Kramer, K.
Lamb wave lenses with conical refracting surfaces are fabricated for use at 400 MHz and 1 GHz. The conical surfaces are ground and polished with mechanical means and they are sufficiently smooth for the frequencies of interest. The wide bandwidth of transducers allow frequency tuning necessary for Lamb wave lenses. The fabricated lenses show the expected V(Z) performance. At high frequencies the attenuation in the coupling medium can be very high, but due to the smaller wavelength the resolution is better and defocus distance can be reduced. Inherently higher leaky wave sensitivity of Lamb wave lens enables a good V(Z) characterization ability at higher frequencies as compared to the conventional spherical lens. Subsurface imaging with these Lamb wave lenses gives satisfactory results for layered structures. Chosen object has leaky wave modes within the angular coverage of the lens. The images exhibit a resolution close to the diffraction limit. Experimental V(Z) curves obtained with these lenses along with images are presented.
Open Access
Computer vision based text and equation editor for LATEX
(IEEE, 2004-06) Öksüz, Özcan; Güdükbay, Uğur; Çetin, Enis
In this paper, we present a computer vision based text and equation editor for LATEX. The user writes text and equations on paper and a camera attached to a computer records actions of the user. In particular, positions of the pen-tip in consecutive image frames are detected. Next, directional and positional information about characters are calculated using these positions. Then, this information is used for on-line character classification. After characters and symbols are found, corresponding LATEX code is generated.
Open Access
Negative refraction and subwavelength focusing using photonic crystals
(SPIE, 2005-01) Özbay, Ekmel; Aydın, Koray; Alıcı, Kamil Boratay; Güven, Kaan
We review certain novel optical properties of two-dimensional dielectric photonic crystals (PCs) which exhibit negative refraction behavior. We investigate two mechanisms which utilize the band structure of the PC and lead to a negative effective index of refraction (neff < 0). The negative refraction phenomenon is demonstrated experimentally and by simulations when the incident beam couples to a photonic band with neff < 0. Further, the PC slab acts like a focusing lens to an omnidirectional source where the properties of focusing depends on the details of the band structure. In one case, by utilizing the TM polarized first band, an image of the source can be formed in the vicinity of the interface with subwavelength resolution. In another case, a TE polarized upper band is used which is able to focus the omnidirectional field far away from the interface with a resolution on par with the wavelength. In the latter case, we explicitly show the flat lens behavior of the structure. These examples indicate that PC based lenses can surpass limitations of conventional lenses and greatly enhance and extend optics applications.
Open Access
Nonrectangular wavelets for multiresolution mesh analysis and compression
(SPIE, 2006) Köse, Kıvanç; Çetin, A. Enis; Güdükbay, Uğur; Onural, Levent
We propose a new Set Partitioning In Hierarchical Trees (SPIHT) based mesh compression framework. The 3D mesh is first transformed to 2D images on a regular grid structure. Then, this image-like representation is wavelet transformed and SPIHT is applied on the wavelet domain data. The method is progressive because the resolution of the reconstructed mesh can be changed by varying the length of the ID data stream created by SPIHT algorithm. Nearly perfect reconstruction is possible if full length of 1D data is received.