Abstract: A method is disclosed for thresholding the luminance component of color picture elements (pels) prior to compression. The method is most effective when used with discrete color images, such as documents having areas of nominally constant color. The method uses spatial information rather than histogram information to threshold the image data. Each scan line is defined as having a series of pel runs. A pel is considered to be in a run if its luminance is within a certain range of an average luminance based on preceding pels. Each run may end in a transition region wherein the luminance of each pel differs from the luminance of the preceding pel by more than a predetermined amount. Where a transition region is found, a local threshold is set based on the average luminance of the preceding run and of the following pel. All pels in the transition region are assigned a luminance value equal either to the average luminance of the preceding run or the actual luminance of the following pel.

Abstract: For use in a teleconference system, a method of reducing line width variations, which are assumed to be the result of undersampling of the original image. Bilevel data received at a remote site is written into a pair of two-dimensional storage arrays. Data stored in the first array is examined row by row to identify different length-dependent classes of black horizontal pel runs. White or black pels in the second array are overwritten with gray pels at specific pel locations as a function of run length to reduce variations in length. The first array data is then examined on a column by column basis. Black vertical runs are classified and the second array is overwritten with gray pels using the same rules as were applied to horizontal runs. The trilevel second array data may be used to drive a display monitor or may first be subjected to further image processing.

Abstract: A technique for enhancing a displayed image originally stored at a density of 1 data bit per pel. The stored data is scanned to locate unit steps, one-row or one-column steps in binary values. Whenever a unit step is found, the distance from the step to the nearest transitions on both sides of the step are found. The distances are used to access lookup tables which assign 4 bit gray scale values to limited numbers of pels on both sides of the unit step. The assigned gray scale values produce a gradually-darkening string of pels extending through the step. When the entire image field has been scanned, a maximum 4 bit pel value is assigned to any unmodified pel having an original binary value of 1 and a minimum pel value is assigned to any unmodified pel having an original binary value of 0. The visual quality of the displayed image is enhanced by the selective introduction of intermediate gray scale values for pels adjacent unit steps.

Abstract: An improved clock retiming system for pulse coded data is provided in which the clock signals are extracted from the encoded data and first and second signals of the same amplitude and frequency but of different phase are generated from the clock signals. First and second amplifiers having variable gains provide amplification for the first and second signals, respectively. The first and second amplified signals are summed to produce a third signal having a phase which is a function of the relative amplitudes of the first and second amplified signals. The original pulse encoded data is sampled with the third signal to produce the retimed data output. The original pulse encoded data is also utilized to sample the third signal. The resulting signal is filtered to provide a DC voltage feedback error signal indicative of the phase difference between the third signal and the original pulse encoded data.

Abstract: An acoustical wave filter is formed by depositing a pattern of interdigitated conductors which form a coding arrangement on a piezeoelectric crystal. Multiplex communication through the crystal is achieved by depositing input filters of differing configuration on the crystals, which separate channels by autocorrelation of a pulse code. A single output filter is provided to respond to the waves set up in the crystal by the input filters to transmit these waves to a single common conductor. Demultiplex is similarly done on a second crystal.

Abstract: A .[.two-phase.]. superconductive shift register using Josephson tunnelling devices is provided wherein a plurality of shift register stages each includes a first and second branch in parallel to which a DC current is supplied. A Josephson tunnelling device is located in each branch which operates in its no voltage state when the DC current is applied thereto. A first and second input means is provided for switching one of the Josephson tunnelling devices in accordance with an input to cause the input current to flow through the other branch. A first and second .[.coupling.]. .Iadd.control .Iaddend.means are located between the stages of the shift register, the first .[.coupling.]. .Iadd.control .Iaddend.means coupling the first branch circuits of successive stages and the second .[.coupling.]. .Iadd.control .Iaddend.means coupling second branch circuits of successive stages. The .[.coupling.]. .Iadd.control .Iaddend.means are .[.energized.]. .Iadd.effective .Iaddend.