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A template ranking with all possible 3×3 templates (mirrors, rotations and reverses of each pattern have the same score).

Data hiding is a technique used to embed a sequence of bits in a host image with small visual deterioration and the means to extract it afterwards. Reversible data hiding allows, in addition, recovering the original cover-image exactly. Several reversible data hiding techniques have been developed but very few of them are appropriate for binary images. This paper proposes a reversible data hiding technique for binary images. This technique uses the Golomb code to compress prediction errors of low-visibility pixels, using its neighborhood as side information, to obtain the space to store the hidden data. The proposed technique is then used to reversibly authenticate binary images, including texts, drawings and halftones. All binary images we tested could be authenticated using the proposed technique, except unrealistically small or random images.

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The changes in phase, time and frequency suffered by signals when retransmitted by a remote and inaccessible transponder and the propagation delays are major constraints to obtain accurate ranging measurements in various related applications. We present a new method and system to determine these delays for every single pulsed signal transmission. The process utilizes four ground-based reference stations, synchronized in time and installed at well known geodesic coordinates. The repeater station is located within the fields of view common to the four reference bases, such as in a platform transported by a satellite, balloon, aircraft, etc. Signal transmitted by one of the reference bases is retransmitted by the transponder, received back by the four bases, producing four ranging measurements which are processed to determine uniquely the time delays undergone in every retransmission process. The repeater's positions with respect to each group of three out of four reference bases are given by a system of equations. A minimization function is derived comparing repeater's positions referred to at least two groups of three reference bases. The minimum found by iterative methods provide the signal transit time at the repeater and propagation delays, providing the correct repeater position. The method is applicable to the transponder platform positioning and navigation, time synchronization of remote clocks, and location of targets. The algorithm has been fully demonstrated simulated for practical situation with the transponder carried by an aircraft moving over bases on the ground. The errors of the determinations have been evaluated for uncertainties in clock synchronization, in propagation time delays and other system parameters.