Apparatus and method for correcting registration errors and trailing phenomenon in a printed image

A color image forming apparatus constructed to form an image by correcting registration shifts during an image forming process by using image data, the color image forming apparatus comprising:

• a registration means for correcting registration shifts by performing a subscan direction line shifting at a line shifting point according to an amount of registration shifts;
• a binarizing means for deciding whether or not to correct grayscale levels of image data, wherein one of a first threshold and a second threshold is used to binarize multivalued image data based on a result of the decision;
• a generating means for generating a reference window comprising a group of the binarized image data;
• a checking means for checking whether the line shifting point is included in the generated reference window;
• a selecting means for selecting a first trailing phenomenon prevention pattern for line shifting pattern matching in a case where the line shifting point is decided to be included in the reference window, and for selecting a second trailing phenomenon prevention pattern for normal pattern matching in a case where the line shifting point is decided to be not included in the reference window;
• a comparing means for comparing the reference window with the first trailing phenomenon prevention pattern in a case where the line shifting point is decided to be included in the reference window, and for comparing the reference window with the second trailing phenomenon prevention pattern in a case where the line shifting point is decided to be not included in the reference window;
• a thinning means for thinning a pixel of the multivalued image data located at the pixel of interest in the reference window, in a case where the comparison by the comparing means finds a match;
• and
• a correcting means for correcting, for interpolation of less than one pixel of image data, grayscale levels of the thinned multivalued image data.

A color image forming method for forming an image by correcting registration shifts during an image forming process by using image data, the color image forming method comprising:

• a registration step to correct registration shifts by performing a subscan direction line shifting at a line shifting point according to an amount of registration shifts;
• a binarizing step to decide whether or not to correct grayscale levels of image data, wherein one of a first threshold and a second threshold is used to binarize multivalued image data based on a result of the decision;
• a generating step to generate a reference window comprising a group of the binarized image data;
• a checking step to check whether the line shifting point is included in the generated reference window;
• a selecting step to select a first trailing phenomenon prevention pattern for line shifting pattern matching in a case where the line shifting point is decided to be included in the reference window, and to select a second trailing phenomenon prevention pattern for normal pattern matching in a case where the line shifting point is decided to be not included in the reference window;
• a step to compare the reference window with the first trailing phenomenon prevention pattern in a case where the line shifting point is decided to be included in the reference window, and to compare the reference window with the second trailing phenomenon prevention pattern in a case where the line shifting point is decided to be not included in the reference window;
• a thinning step to thin a pixel of the multivalued image data located at a pixel of interest in the reference window, in a case where the comparison by the comparing means finds a match;
• and
• a correcting step to correct, for interpolation of less than one pixel of image data, grayscale levels of the thinned multivalued image data.

A computer-readable recording medium having computer-executable instructions for performing a color image forming method, the color image forming method forming an image by correcting registration shifts during an image forming process by using image data, the method comprising the steps of:

• correcting registration shifts by performing a subscan direction line shifting at a line shifting point according to an amount of registration shifts;
• deciding whether or not to correct grayscale levels of image data, wherein one of a first threshold and a second threshold is used to binarize multivalued image data based on a result of the decision;
• creating a reference window comprising a group of the binarized image data;
• checking whether the line shifting point is included in the generated reference window;
• selecting a first trailing phenomenon prevention pattern for line shifting pattern matching in a case where the line shifting point is decided to be included in the reference window, and selecting a second trailing phenomenon prevention pattern for normal pattern matching in a case where the line shifting point is decided to be not included in the reference window;
• comparing the reference window with the first trailing phenomenon prevention pattern in a case where the line shifting point is decided to be included in the reference window, and comparing the reference window with the second trailing phenomenon prevention pattern in a case where the line shifting point is decided to be included in the reference window;
• and
• thinning a pixel of the multivalued image data located at a pixel of interest in the reference window in a case where the comparison by the comparing step finds a match;
• and
• correcting, for interpolation of less than one pixel of image data, grayscale levels of the thinned multivalued image data.