High addressability error diffusion with minimum mark size

Claim 1

A method of preparing a set of high addressability image signals, representing the optical density of an image, for reproduction with a high addressability output device, said output device operating at a resolution on m spots per unit length in a first direction and n spots per unit length in a second direction perpendicular to the first direction, and having an output spot size greater than 1/m×1/n, the steps comprising: receiving at an input each high addressability Image signal in the set thereof, prepared for reproduction having a resolution of m×n and with a possible optical density levels, where c>2, for printing at a high addressability output device having a resolution of m×n with do possible optical density levels, where a>d, where d>1; producing a preliminary output signal that is one of said d possible optical density levels, responsive to a comparison of each high addressability image signal to a threshold signal from a threshold signal source; producing a final output signal in response to the level of the preliminary output signal, the level of any immediately preceding final output signal, and a counted number of final output signals since the last variation in optical density level in a final output signal from a current optical density level, wherein said final output signal is one of said possible optical density levels printable at a high addressability output device; storing to an error term storage device, an error signal that has a level equal to the difference between the final output signal and the high addressability image signal; and determining an error correction signal or signals, as a weighted portion of the stored error signal, to be used in modifying at least one subsequent high addressability image signal in the set thereof, prior to any other operation thereon.

Claim 2

A method of preparing a set of high addressability image signals, representing the optical density of an image, for reproduction with a high addressability output device, said output device operating at a resolution on m spots per unit length in a first direction and n spots per unit length in a second direction perpendicular to the first direction, and having an output spot size greater than 1/m×1/n, the steps comprising: receiving at an input each high addressability Image signal in the set thereof, prepared for reproduction having a resolution of m×n and with a possible optical density levels, where c>2, for printing at a high addressability output device having a resolution of m×n with do possible optical density levels, where a>d, where d>1; producing a preliminary output signal that is one of said d possible optical density levels, responsive to a comparison of each high addressability image signal to a threshold signal from a threshold signal source; producing a final output signal in response to the level of the preliminary output signal, the level of any immediately preceding final output signal, and a counted number of final output signals since the last variation in optical density level in a final output signal from a current optical density level, wherein said final output signal is one of said possible optical density levels printable at a high addressability output device; storing to an error term storage device, an error signal that has a level equal to the difference between the final output signal and the high addressability image signal; and determining an error correction signal or signals, as a weighted portion of the stored error signal, to be used in modifying at least one subsequent high addressability image signal in the set thereof, prior to any other operation thereon.

Claim 5

An apparatus for preparing high addressability image signals representing the optical density of an image, for output to a high addressability output device operating at a resolution of me×no spots per unit length with an output spot size greater than am×1/no. comprising; an input to which a high addressability image signal is directed, said high addressability image signal prepared for reproduction at a resolution of m×n, and one of c possible optical density levels, where c >2, for printing at a high addressability printer operating to reproduce images at a resolution of m×n and with d possible optical density levels, where c>d>1 a thresholding comparator comparing the high addressability image signal to at least one threshold signal directed to the thresholding comparator from a threshold signal source and providing a preliminary output signal at one of said d optical density levels responsive to said comparison means for producing a final output signal responsive to the level of the preliminary output signal, a level of any immediately preceding final output signal, and a counted number of final output signals since the last variation in a final output signal from a current optical density level, wherein said final output signal is one said d possible optical density levels printable at a high addressability output device; and an error diffusion feedback arrangement including: a signal inverter connected to said final output signal producing means, changing the polarity of the final output signal for the error feedback arrangement, an error adder, connected to the signal inverter and the signal adder, and determining the difference between the changed polarity signal output signal and the high addressability image signal, means for generating at least one error correction signal, connected to the error adder, said error correction signal generated as a weighted portion of the error signal, and an error delay buffer, storing error correction signals for subsequent direction to a signal adder; a signal adder, receiving error correction signals and adding said error correction signals to each subsequent high addressability image signal in the set thereof, prior to any other operation thereon after receipt at the input.

Claim 6

An apparatus for preparing high addressability image signals representing the optical density of an image, for output to a high addressability output device operating at a resolution of me×no spots per unit length with an output spot size greater than am×1/no. comprising; an input to which a high addressability image signal is directed, said high addressability image signal prepared for reproduction at a resolution of m×n, and one of c possible optical density levels, where c >2, for printing at a high addressability printer operating to reproduce images at a resolution of m×n and with d possible optical density levels, where c>d>1 a thresholding comparator comparing the high addressability image signal to at least one threshold signal directed to the thresholding comparator from a threshold signal source and providing a preliminary output signal at one of said d optical density levels responsive to said comparison means for producing a final output signal responsive to the level of the preliminary output signal, a level of any immediately preceding final output signal, and a counted number of final output signals since the last variation in a final output signal from a current optical density level, wherein said final output signal is one said d possible optical density levels printable at a high addressability output device; and an error diffusion feedback arrangement including: a signal inverter connected to said final output signal producing means, changing the polarity of the final output signal for the error feedback arrangement, an error adder, connected to the signal inverter and the signal adder, and determining the difference between the changed polarity signal output signal and the high addressability image signal, means for generating at least one error correction signal, connected to the error adder, said error correction signal generated as a weighted portion of the error signal, and an error delay buffer, storing error correction signals for subsequent direction to a signal adder; a signal adder, receiving error correction signals and adding said error correction signals to each subsequent high addressability image signal in the set thereof, prior to any other operation thereon after receipt at the input.