Abstract: An improved color picture tube (10) has a shadow mask (24) mounted therein in spaced relation to a viewing screen (22) thereof. The mask has a rectangular periphery with two long sides and two short sides. A major axis (X) passes through the center of the mask and parallels the long sides thereof, and a minor axis (Y) passes through the center of the mask and parallels the short sides thereof. The mask has an aperture array (35) that includes slit-shaped apertures (36) aligned in columns (37) that essentially parallel the minor axis and end at a border of the aperture array. The improvement comprises the column-to-column spacing (aH) parallel to the major axis including a pseudo-cyclic variation at least in a portion of the mask, wherein a complete cycle within the pseudo-cyclic variation occurs in the column-to-column spacings between no more than nine consecutive columns.

Abstract: In a predictive encoding circuit the transmission of prediction errors to the predictive decoding circuit is selectively suppressed and prediction errors having a predetermined value are applied to the prediction circuit in both the encoding circuit and in the decoding circuit, instead of the non-transmitted prediction errors. In order to determine which prediction errors are not transmitted, a masking function value is determined for an actual pixel in the encoding circuit. This is a linear combination of weighted difference between two pixel values of a predetermined cluster of pixels located in the vicinity of the actual pixel. The actual prediction error is not transmitted only if, for example this masking function value is within a certain range and the previous prediction error has been transmitted. In the decoding circuit the masking function values are determined, starting from the regained local pixel values.