P. De Neve

The use of a modified Westcott-formalism in the ko-standardization of NAA: The state of affairs

Recently, the introduction was proposed of the Westcott-formalism in the ko-standardization method, in order to enable the handling of analytically important “non-1/v” (n, γ) reactions. In the present paper some elucidations are given to the “Westcott-based”ko-method: the black box of Westcotts “g+rs” formalism is opened; procedures and formulas are given for the experimental determination of the flux parameters and a survey is presented of the status of the nuclear data.

Rate-distortion performance of H.264/AVC compared to state-of-the-art video codecs

In the domain of digital video coding, new technologies and solutions are emerging in a fast pace, targeting the needs of the evolving multimedia landscape. One of the questions that arises is how to assess these different video coding technologies in terms of compression efficiency. In this paper, several compression schemes are compared by means of peak signal-to-noise ratio (PSNR) and just noticeable difference (JND). The codecs examined are XviD 0.9.1 (conform to the MPEG-4 Visual Simple Profile), DivX 5.1 (implementing the MPEG-4 Visual Advanced Simple Profile), Windows Media Video 9, MC-EZBC and H.264/AVC AHM 2.0 (version JM 6.1 of the reference software, extended with rate control). The latter plays a key role in this comparison because the H.264/AVC standard can be considered as the de facto benchmark in the field of digital video coding. The obtained results show that H.264/AVC AHM 2.0 outperforms current proprietary and standards-based implementations in almost all cases. Another observation is that the choice of a particular quality metric can influence general statements about the relation between the different codecs.

Psychovisual Evaluation of Lossy CMYK Image Compression for Printing Applications

In the digital prepress workflow, images are represented in the CMYK colour space. Lossy image compression alleviates the need for high storage and bandwidth capacities, resulting from the high spatial and tonal resolution. After the image has been printed on paper, the introduced visual quality loss should not be noticeable to a human observer. Since visual image quality depends on the compression algorithm both quantitatively and qualitatively, and since no visual image quality models incorporating the end‐to‐end image reproduction process are satisfactory, an experimental comparison is the only viable way to quantify subjective image quality. This paper presents the results from an intensive psychovisual study based on a two‐alternative forced‐choice approach involving 164 people, with expert and non‐expert observers distinguished. The primary goal is to evaluate two previously published adaptations of JPEG to CMYK images, and to determine a visually lossless compression ratio threshold for typical printing applications. The improvements are based on tonal decorrelation and overlapping block transforms. Results on three typical prepress test images indicate that the proposed adaptations are useful and that for the investigated printing configuration, compression ratios up to 20 can be used safely.

An Advanced Color Representation for Lossy Compression of CMYK Prepress Images

CMYK color images are used extensively in prepress applications. When compressing those color images one has to deal with four different color channels. Usually compression algorithms only take into account the spatial redundancy that is present in the image data. This approach does not yield an optimal data reduction since there also exists a high correlation between the different colors in natural images.

A comparative study of lossless coding techniques for screened continuous-tone images

The huge sizes of screened colour-separated photographic images makes lossless compression very beneficial for both storage and transmission. Because of the special structure induced by the half-tone dots, the compression results obtained on the CCITT test images might not apply to high-resolution screened images and the default parameters of existing compression algorithms may not be optimal. In this paper we compare the performance of different classes of lossless coders: general-purpose one-dimensional coders, non-adaptive two-dimensional black-and-white coders and adaptive two-dimensional coders. Firstly, experiments on a set of test images screened under different conditions showed that MGBILEVEL and JBIG perform best with respect to compression efficiency; the difference with the other coders is significant. Secondly, we investigated the influence of the screening method (stochastic or classical screening) and screening resolution on the compression ratio for these techniques.

Importance of double neutron-capture as a second-order reaction interference in NAA

An investigation is made of the importance of (n,γ,n,γβ−) second-order reaction interferences in reactor neutron activation analysis (NAA), in addition to the commonly considered (n, γ, β−; n, γ) interferences. The algorithms for the calculation of the interference are derived from the Bateman-Rubinson equation, taking into account the formation of all m-and g-states involved bum-up effects, and the growth of the interfering radionuclide after irradiation due to a mother-daughter relationship. The following practical cases are examined in detail:138Ba→140La (detemination of La in presence of excess Ba),139La→141Ce (Ce in La),164Dy→166Ho (Ho in Dy),186W→188Re (Re in W) and192Os→194Ir (Ir in Os). A computer search was done for the nuclear data involved in the computation. For139La[(n,γ; n,γ; β−)+(n,γ;β−; n,γ)]141Ce, and164Dy[(n,γ; n,γ; β−)+ (n,γ; β−; n,γ)]166Ho experimental checks were performed in the Budapest Research Reactor, which confirmed the calculations showing that the (n,γ; n,γ; β−) interference gives the largest contribution to the apparent concentration of Ce in La and of Ho in Dy, respectively.