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A CSS-sprite packing problem is considered in this article. CSS-sprite is a technique of combining many pictures of a web page into one image for the purpose of reducing network transfer time. The CSS-sprite packing problem is formulated here as an optimization challenge. The significance of geometric packing, image compression and communication performance is discussed. A mathematical model for constructing multiple sprites and optimization of load time is proposed. The impact of PNG-sprite aspect ratio on file size is studied experimentally. Benchmarking of real user web browsers communication performance covers latency, bandwidth, number of concurrent channels as well as speedup from parallel download. Existing software for building CSS-sprites is reviewed. A novel method, called Spritepack , is proposed and evaluated. Spritepack outperforms current software.

What is the minimum tour visiting all lines in a subway network? In this paper we study the problem of constructing the shortest tour visiting all lines of a city railway system. This combinatorial optimization problem has links with the classic graph circuit problems and operations research. A broad set of fast algorithms is proposed and evaluated on simulated networks and example cities of the world. We analyze the trade-off between algorithm runtime and solution quality. Time evolution of the trade-off is also captured. Then, the algorithms are tested on a range of instances with diverse features. On the basis of the algorithm performance, measured with various quality indicators, we draw conclusions on the nature of the above combinatorial problem and the tacit assumptions made while designing the algorithms.

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