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    PublicationOpen Access
    Content-aware scalability-type selection for rate adaptation of scalable video
    (Springer, 2007) Akyol, Emrah; Civanlar, M. Reha; (TBD); Tekalp, Ahmet Murat; Faculty Member; (TBD); College of Engineering; 26207
    Scalable video coders provide different scaling options, such as temporal, spatial, and SNR scalabilities, where rate reduction by discarding enhancement layers of different scalability-type results in different kinds and/or levels of visual distortion depend on the content and bitrate. This dependency between scalability type, video content, and bitrate is not well investigated in the literature. To this effect, we first propose an objective function that quantifies flatness, blockiness, blurriness, and temporal jerkiness artifacts caused by rate reduction by spatial size, frame rate, and quantization parameter scaling. Next, the weights of this objective function are determined for different content (shot) types and different bitrates using a training procedure with subjective evaluation. Finally, a method is proposed for choosing the best scaling type for each temporal segment that results in minimum visual distortion according to this objective function given the content type of temporal segments. Two subjective tests have been performed to validate the proposed procedure for content-aware selection of the best scalability type on soccer videos. Soccer videos scaled from 600 kbps to 100 kbps by the proposed content- aware selection of scalability type have been found visually superior to those that are scaled using a single scalability option over the whole sequence.
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    Lamellar grating interferometer based compact ft spectrometers
    (IEEE, 2009) N/A; N/A; (TBD); Ferhanoğlu, Onur; Seren, Hüseyin Rahmi; Ürey, Hakan; PhD Student; Master Student; Faculty Member; (TBD); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 205198; N/A; 8579
    Lamellar grating interferometers (LGI) offer compact spectrometer architecture with high spectral resolution and large clear aperture. This study investigates the diffraction based inherent limitations of LGI spectrometers in contrary to conventional Michelson type spectrometer architecture. Simulations and experiments were conducted to demonstrate and explain periodic nature of the interferogram envelope due to Talbot image formation. Simulations reveal that grating period should be chosen large enough to avoid Talbot phase reversal at the expense of mixing diffraction orders. Overall optimization effort on the LGI system reveals that it is possible to build compact spectrometers to be used directly in the field without any performance degradation in contrary to bulky FTIR systems.