The invention provides a method and apparatus for correcting shading distortion in a source of scanned video signal. A multiple location store is provided for storing a signal indicative of the shading correction required at each of a number of selected, spaced apart points in the scannable region of the source and signal interpolation means is provided for interpolating between the stores values of correction in both line and frame scan directions for other points in the region. The invention also provides a method and apparatus for loading the correction signals into the store locations automatically during a number of frame scans of the region. This is achieved by correcting the video signal at each point by a known amount, comparing the corrected signal with a reference signal and storing a signal indicative of this amount of correction if the comparison indicates that the correction has improved the shading of the video signal. The final correction signal stored at each store location is derived by a method of successive approximations.
Television circuit comprising a signal correction circuit which is active on signal recording and display, respectively, to obtain an optimum picture on display, and comprising a memory, memory-location (RC) containing correction information of which correspond to picture subregions (RC), each having their scanning lines (H1-H16), these subregions (RC) having been arranged in a matrix of rows and columns. According to the invention the memory comprises further memory locations (HOC) namely a first, further memory location (HOC1-HOC7) for each column of subregions, absolute correction information being present in each first further memory location for all subregions in the column and relative difference information being present in each memory location (R1C1-R19C7) corresponding to a subregion in the column, each relative difference information per subregion furnishing a correction information for each scanning line in the subregion which information is valid with respect to the preceding scanning line. At a linearity correction of, for example, the horizontal line scan a more or less vertical, shifted, curved information line 4 can be corrected to form a vertical, straight line 3 in the exact position, by means of, for example, an absolute correction from a point 4.sub.1 to a point 3.sub.1 and a relative difference correction over sixteen scanning lines H, across the distance difference in the direction of line scan between the points 4.sub.1 and 4.sub.2, 4.sub.2 and 4.sub.3, etc.
A spatial correction device for an image analyzer having an image restitution support medium and a device for scanning the support medium. A memory is provided for storing, for each of the MN rectangles resulting from dividing the image restitution support medium of the analyzer into a grid of M groups of L lines each and N columns, a predetermined correction signal. Also included is a sequencer for ensuring that the correction signals are properly applied as well as an interpolation device for calculating the intermediate values of the correction signals corresponding to each of the L lines of a given rectangle. This interpolation device also avoids the derivative ruptures of the correction signals during their transition between adjacent rectangles which are situated in the same column.
Precise, point-by-point correction of spatial and shading errors in a camera television picture are performed manually. The errors to be corrected are determined by visually examining a picture on a video monitor, by selecting an area for error correction which area corresponds to the type and extent of the specific error selected for correction. A position command increments or decrements an address by preselected steps to locate a movable "cursor" which, in turn, identifies the area being corrected. A correction command retrieves the data from the area identified, and which contains the error, selectively increments or decrements the data in preselected steps, and stores the new data back in memory. The process continues until the operator is satisfied with the correction results. Correction thus may be made point-by-point, along horizontal or vertical lines or areas, in selected corner areas, etc., of the picture.
A signal analyzing circuit for a periodically occurring signal such as from a video signal source (VSS). The circuit comprises a store (m) having separate store locations m associated with corresponding regions defined as rows and columns of a picture display of the periodically occurring video signal. In addition, a time signal generator (TG) is provided for the synchronous control of the video signal source (VSS) and the store (m). For filling in a simple manner, without disturbance, the store locations (m) with the mean value of the video signal taken per accurately determined region, the output of the signal source (VSS) is coupled via an analog-to-digital converter (A/D) to counting inputs of a number of counters (BC1 to BC7) equal to the number of regions per row. The counters are operative sequentially and periodically. Each counter (BC1 to BC7) is followed by a buffer register (BR1 to BR7) receiving the counting information in the line blanking period at the end of the last signal period in the row of regions and the counter (BC) is subsequently reset. The buffer register (BR) is followed by the store (m) with the separate store locations (m), which are filled with the previous counting information during the next counting operation.
A signal processing method for eliminating fixed error sources in the video signal of a pyroelectric vidicon comprising the step of adding the signal value at each point of the pyroelectric plate to previous signal values relating to the same point for forming an integrated or mean value for a great number of signal values at each point and then subtracting the fixed error estimate from the signal values in the latest received video signal. This mean value, if differing from zero, is the estimate of the fixed error at the respective point.
