Proc. SPIE. 8768, International Conference on Graphic and Image Processing (ICGIP 2012)
KEYWORDS: Signal to noise ratio, Image compression, Receivers, Computer programming, Discrete wavelet transforms, Personal digital assistants, Image transmission, Bismuth, Error control coding, Rubidium
The SPIHT (set partitioning in hierarchical trees) algorithm, which works with the aid of the discrete wavelet
transform (DWT), is one of the most renowned techniques for image compression. One problem with SPIHT image
coding, especially when image transmission is involved, is that even just as few as one error in the embedded code
sequence can render the decoded image completely unrecognizable. In this paper, we propose a scheme in which an
SPIHT code sequence is packetized into two types: CP (critical packet) and RP (refinement packet). Then, we address
the transmission of those SPIHT packets over erasure channels. The basic idea is to provide unequal error protection
(UEP) to those packets by diversity (i.e., repeated transmissions) so that, at the receiver, the decoded image quality
(measured in the expected SNR, signal-to-noise-ratio) is as good as possible. A diversity allocation (DA) algorithm,
referred to as progressive diversity allocation (PDA), is proposed. It works in a fashion and is naturally compatible with
the progressive transmission of SPIHT-encoded images. Experiments show that the PDA scheme produces good results,
nearly as good as achieved by the method of full search.
Stability of organic photovoltaic cells is the key issue for their commercialization. Despite intensive investigations to clarify the causes of failure of devices, the process of degradation is not yet well understood. In this work, we made use of the trap measurements by the charge-based deep-level transient spectroscopy to study devices that have been aged by continuous exposure to artificial sunlight for 20 h, and we compared the trap parameters to those obtained in freshly prepared samples. With regard to poly (3-hexylthiophene) (P3HT)-based devices, the P3HT:phenyl C61 butyric acid methyl ester blend cells showed an additional deep trap level and a higher trap density. In the degraded devices, all the existing traps in the fresh sample were found, and there was no creation of additional defect levels. The density of several trap levels in the polymer was strongly reduced after aging. Analysis of the results suggests that a phase separation in the photoactive blend has occurred, leading to a better organization of the polymer domains to lower defect states.