Method and apparatus for gamma correction by mapping, transforming and demapping

A method for producing physical signals representing a power function approximation of an input value which is included within a predefined portion of a predefined input value range, said portion of said input value range being divided into a plurality of segments, one of said segments being a standard segment, and one of said segments including said input value and being an input value segment, comprising the steps of:

• processing input physical signals representing said input value to produce mapped physical signals, said mapped physical signals representing a mapped value being a mapped version of said input value from said input value segment to said standard segment;
• processing said mapped physical signals to produce converted physical signals, said converted physical signals representing a converted value being at least an approximation of said power function of said mapped value;
• and
• processing said converted physical signals to produce output physical signals, said output physical signals representing an output value being a de-mapped version, from said standard segment to said input value segment, of said converted value.

A method for pre-correcting a color input value for gamma-distortion of the light output of a phosphor as a function of the driving voltage applied to an electron beam incident on said phosphor, said color input value being included within a predefined portion of a predefined input value range, said portion of said input value range being divided into a plurality of segments, one of said segments being a standard segment, and one of said segments including said input value and being an input value segment, comprising the steps of:

• processing input physical signals representing said input value to produce mapped physical signals, said mapped physical signals representing a mapped version of said input value from said input value segment to said standard segment;
• processing said mapped physical signals to produce converted physical signals, said converted physical signals representing at least an approximation of a gamma correction function of said mapped version of said input value;
• and
• processing said converted physical signals to produce output physical signals, said output physical signals representing a de-mapped version, from said standard segment to said input value segment, of said approximation of said gamma correction function of said mapped version of said input value.

A method for pre-correcting color input values for gamma-distortion of the light output of a phosphor as a function of the driving voltage applied to an electron beam incident on said phosphor, each of said color input values defining a color value for a respective one of a plurality of pixels on a surface carrying said phosphor, said plurality of pixels cooperating to form an image, each of said color input values being included within a predefined portion of a predefined input value range, said portion of said input value range being divided into a plurality of segments, one of said segments being a standard segment, and each of said input values being included within a respective input value segment, comprising the steps of:

• mapping each of said input values which is not already within said standard segment, by a mapping function from the input value segment of the input value to said standard segment, to form respective mapped values;
• converting each of said mapped values by at least an approximation of said gamma correction function of said mapped values, to form respective converted values;
• de-mapping each of said converted values which did not derive from an input value which was within said standard segment, by a de-mapping function from said standard segment to the input value segment of the input value from which the converted value derived, to form respective corrected values;
• and
• providing said corrected values for application as a driving voltage for an electron beam incident on said phosphor at a position on said surface corresponding to each respective one of said pixels.

A method for pre-correcting color input values for gamma-distortion of the light output of a phosphor as a function of the driving voltage applied to an electron beam incident on said phosphor, each of said color input values defining a color value for a respective one of a plurality of pixels on a surface carrying said phosphor, said plurality of pixels cooperating to form at least part of an image, each of said color input values being represented in binary by a respective group of input physical signals, comprising the steps of:

• determining the number of bit positions in each given one of said groups of input physical signals between the most significant one of said bit positions in said group and the most significant one of said bit positions in said group which is carrying a signal representing a logic 1;
• left-shifting said given group of input physical signals by said number of bit positions to provide a given group of mapped physical signals representing a given mapped value;
• converting said given mapped value by at least a linear approximation of said gamma correction function, to form a given converted value represented by a given group of converted physical signals;
• providing said given group of converted physical signals to a first input port of multiplying circuitry, said multiplying circuitry having a second input port indicating which of a plurality of different multipliers by which the value represented on said first input port is to be multiplied;
• and
• providing said number of bit positions for said given one of said input values to said second input port of said multiplying circuitry, said multiplying circuitry providing through an output port a given group of converted physical signals representing a gamma-corrected value for said given input value.

Apparatus for performing a transfer function on any input value within a first input compliance range, comprising:

• mapping circuitry which binary shifts each of said input values by a respective number of bits such that said shifted input values are within a second input compliance range smaller than said first input compliance range;
• conversion circuitry coupled to receive said shifted input values and which converts each of said shifted input values according to said transfer function;
• and
• demapping circuitry coupled to receive said converted values and which demaps each of said converted values by an inverse transformation responsive to the number of bits by which said mapping circuitry shifted the respective input value.

Computation apparatus for use with first input signals representing a sequence of first input values, comprising:

• an encoder having an input coupled to receive said first input signals and having an encoder output, said encoder providing on said encoder output a signal indicating the number of bit positions between a fixed predetermined bit position and the bit position of the highest order logic 1 present in each input value represented by said first input signals, at least when said number of bit positions is within a predefined set;
• a shifter coupled to receive said first input signals and said encoder output, said shifter having an output and providing on said output a version of each of said first input signals binary shifted by the number of bits indicated by said encoder output, at least when said number of bit positions is within a predefined set;
• conversion circuitry having an input coupled to receive said output of said shifter and having an output, said conversion circuitry providing on said conversion circuitry output, signals representing a predefined mathematical function of each of the values represented by the signals on said conversion circuitry input, at least when said number of bit positions is within a predefined set;
• and
• inverse transformation circuitry coupled to receive said conversion circuitry output signals and said encoder output signals, said inverse transformation circuitry having an output and providing on said inverse transformation circuitry output signals representing each of the values represented by said conversion circuitry output signals multiplied a factor responsive to said encoder output signals, at least when said number of bit positions is within a predefined set.