Color television window for a video display unit

A digital-television/graphics-display interface circuit for receiving digitally-encoded luminance samples and chrominance samples representing a color-television signal for a live color-television image from a digital-television decoder at a predetermined lines-per-frame number of television lines per frame and a predetermined samples-per-line number of luminance samples per full-length television line and transmitting selected ones of the luminance samples and the chrominance samples to a frame buffer for storage in destination-window-area memory locations, which memory locations are associated with a destination-window area of a graphics display, for display as a source-window portion of the live color-television image in the destination-window area of the graphics display, the destination-window area having a selectable destination-window-height number of rows of pixels and a selectable destination-window-width number of pixels per row, the source-window portion of the color-television image having a selectable source-window-height number of television lines in the source-window portion and a source-window-width number of luminance samples in a television line in the source-window portion, the destination-window-height number of rows of pixels in the destination window area being different from the source-window-height number of television lines in the source-window portion and the destination-window-width number of pixels per row in the destination-window area being different from the source-window-width number of luminance samples in the television line in the source-window portion, the interface circuit comprising:

• (a) a luminance first-in-first-out device having a luminance-sample input, a luminance-sample output, a luminance-shift-in-control-signal input, and a luminance-shift-out-control-signal input, the luminance-sample input of the luminance first-in-first-out device being connectable to a luminance-sample output of the digital-television decoder for controllably shifting in selected ones of the luminance samples received from the digital-television decoder in response to shift-in-control-signals applied to the luminance shift-in-control-signal input, and the luminance-sample output being connectable to a luminance-sample input of the frame buffer of the graphics display for controllably shifting out luminance samples for transmitting to the frame buffer in response to shift-out-control signals applied to the luminance shift-out-control-signal output;
• (b) a chrominance first-in-first-out device having a chrominance-sample input, a chrominance-sample output, a chrominance shift-in-control signal input, and a chrominance shift-out-control signal input, the chrominance-sample input of the chrominance first-in-first-out device being connectable to a chrominance-sample output of the digital-television decoder for controllably shifting in chrominance samples received from the digital-television decoder in response to chrominance shift-in-control-signals applied to the chrominance shift-in-control-signal input, and the chrominance-sample output being connectable to a chrominance-sample input of the frame buffer of the graphics display for controllably shifting out chrominance samples for transmission to the frame buffer in response to chrominance shift-out-control signals applied to the shift-out-control-signal output;
• (c) horizontal window control means connected to the luminance shift-in-control-signal input and the luminance shift-out-control-signal input of the luminance first-in-first-out device and to the chrominance shift-in-control-signal input and the chrominance shift-out-control-signal input of the chrominance first-in-first-out device for controllably enabling the shifting of individual ones of the luminance samples into and out of the luminance first-in-first-out device and for controllably enabling the shifting of individual ones of the chrominance samples into and out of the chrominance first-in-first-out device, the horizontal window control means including a horizontal image-contraction control-pattern memory for storing a binary horizontal image-contraction control pattern, the number of bits in the horizontal image-contraction control pattern being at least as great as the samples-per-line number of luminance samples in a television line, the horizontal window control means being adapted to enable or disable the shifting of individual ones of corresponding luminance and chrominance samples from a television line into the luminance and chrominance first-in-first-out devices, respectively, in accordance with the state of corresponding individual bits in the horizontal image-contraction control pattern stored in the horizontal image-contraction control-pattern memory;
• (d) vertical window control means for controllably enabling and disabling the loading of luminance and chrominance samples from individual ones of the television lines into the frame buffer, the vertical window control means including a vertical image-contraction control-pattern memory for storing a binary vertical image-contraction control pattern, the number of bits in the vertical image-contraction control pattern being at least as great as the lines-per-frame number of television lines, the vertical window control means being adapted to enable or disable the storing of samples from individual ones of the television lines in accordance with the state of corresponding individual bits in the vertical image-contraction control pattern stored in the vertical image-contraction control-pattern memory;
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• (e) computation means connected to the horizontal window control means and to the vertical window control means for generating horizontal image-contraction control patterns for storage in the horizontal image-contraction control-pattern memory of the horizontal window control means, and vertical image-contraction control patterns for storage in the vertical image-contraction control-pattern memory of the vertical window control means, the computation means being adapted to calculate each of the horizontal and vertical image-contraction control patterns essentially by a computer-graphics vector-drawing procedure.