Method and apparatus for minimizing effects of slope overload condition when using differential pulse code modulation scheme

A graphics controller circuit for upscaling a source video image to an upscaled video image, comprising:

• a line buffer for storing source video pixel data of a previous scan line in a compressed pixel format, said line buffer comprising:
• a first predictor for generating a first predicted value for a next source video pixel data of said previous scan line normally from a first recoverer value;
• a first adder for receiving each source video pixel data and a corresponding first predicted value, said first adder generating a difference value of the source video pixel data and the corresponding first predicted value;
• a quantizer for quantizing the difference value to generate a compressed pixel data for the corresponding source pixel data;
• a first recoverer for receiving each of the compressed pixel data and generating said first recoverer value from the compressed pixel data, said first recoverer determining whether a slope overload condition is encountered when said quantizer quantizes the difference value, and forcing said first predicted value for said next pixel data to a different value if said slope overload condition is encountered, wherefore said quantizer avoids a slope overload condition when generating compressed pixel data for said next pixel data;
• a local memory for storing said set of compressed pixel data;
• a second predictor for generating a second predictor value normally from a second recoverer value;
• a second recoverer for receiving said compressed pixel data from said local memory, and generating said second recoverer value for each compressed pixel data, said second recoverer determining whether a slope overload condition is present, and forcing said second predictor to generate a different second predictor value for a next pixel data if said slope overload condition is present, said second recoverer also sending a slope overload condition signal on a slope overload condition signal line;
• and
• a second adder for receiving said second predicted value and said second recoverer value, and generating said pixel data of said previous scan line from said second predicted value;
• a multiplexor for receiving said pixel data of said previous scan line from said second adder and a corresponding pixel data of a present scan line, said multiplexor normally sending on an output line said pixel data of said previous scan line, and said corresponding pixel data of said present scan line when a slope overload condition is encountered under the control of said slope overload condition signal line;
• and
• an interpolator coupled to said multiplexor for generating a set of additional pixel data of said upscaled video image by interpolating said pixel data sent by said multiplexor on said output line and corresponding pixel data of said present scan line.

A circuit for generating a set of compressed pixel data corresponding to a series of pixel data of a scan line, comprising:

• a predictor for generating a predicted value for a next pixel data normally from a recoverer value;
• an adder for receiving each pixel data and a corresponding predicted value, said adder generating a difference value of the pixel data and the corresponding predicted value;
• a quantizer for quantizing the difference value to generate a compressed pixel data for the corresponding pixel data;
• and
• a recoverer for receiving each of the compressed pixel data and generating said recoverer value from the compressed pixel data, said recoverer determining whether a slope overload condition is encountered when said quantizer quantizes the difference value, and forcing said predicted value for said next pixel data to a different value if said slope overload condition is encountered,
• wherefore said quantizer avoids a slope overload condition when generating compressed pixel data for said next pixel data.

A circuit for decompressing a set of decompressed pixel data to generate pixel data of a scan line, comprising:

• a predictor for generating a second predictor value normally from a recoverer value;
• a recoverer for receiving said compressed pixel data, and generating said recoverer value for each compressed pixel data, said recoverer determining whether a slope overload condition is present in compressing said pixel data of said scan line, and forcing said predictor to generate a different predictor value for a next pixel data if said slope overload condition is present;
• and
• an adder for receiving said predicted value and said recoverer value, and generating said pixel data of said previous scan line from said second predicted value.

A computer system for displaying a source video image comprising at least a present scan line and a previous scan line represented by a set of source video pixel data, said computer system comprising:

• a graphics controller circuit for interpolating said set of source video pixel data of a source video image to generate an additional set of pixel data of an upscaled video image, said graphics controller circuit further comprising:
• an interpolator for receiving at least two pixel data comprising a pixel data of said present scan line and a corresponding pixel data of said previous scan line, said interpolator normally interpolating the two pixel data to generate said additional pixel data;
• and
• an override circuit for causing said interpolator to generate said additional pixel data from an adjacent pixel data located adjacent to said pixel data of said previous scan line upon a first condition;
• a display unit for displaying said upscaled video image.

A method of upscaling a source video image to generate an upscaled video image, wherein said source video image comprises at least a present scan line and a previous scan line represented by a set of source video pixel data, said method comprising the steps of:

• receiving at least two pixel data comprising a pixel data of said present scan line and a corresponding pixel data of said previous scan line;
• interpolating normally the two pixel data to generate a set of additional pixel data of said upscaled video image;
• and
• generating said set of additional pixel data from an adjacent pixel data located adjacent to said pixel data of said previous scan line and said pixel data of said present scan line upon a first condition.

A method of generating a set of compressed pixel data corresponding to a series of pixel data of a scan line, said method comprising the steps of:

• generating a predicted value for a next pixel data normally from a recoverer value;
• subtracting each pixel data from a corresponding predicted value to generate a difference value of the pixel data and the corresponding predicted value;
• quantizing the difference value to generate a compressed pixel data for the corresponding pixel data;
• and
• generating said recoverer value from the compressed pixel data;
• determining whether a slope overload condition is encountered in said step of quantizing;
• forcing said predicted value for said next pixel data to a different value if said slope overload condition is encountered for a present pixel data,
• wherefore said quantizer avoids a slope overload condition when generating compressed pixel data for said next pixel data.