Image forming apparatus and its control method of correction amount based on selected rotational speed

A method of controlling an image forming apparatus in which image forming units each having an image carrier, an exposure unit for exposing by drawing a scanning line on the image carrier with a beam, and a developing unit for visualizing an electrostatic latent image generated by the exposing using a color former are juxtaposed in a conveying direction of a print medium, the method comprising:

• a step of storing an image including a plurality of pixels to a memory;
• selecting a rotational speed of an image carrier from among a plurality of rotational speeds of a image carrier;
• setting a size of a print medium;
• calculating a correction amount in a sub-scanning direction of a pixel included in the stored image on the basis of the selected rotational speed, the set size of a print medium and the stored information, wherein the more the selected rotational speed, the greater a correction amount in a sub-scanning direction of a pixel included in the stored image is;
• a coordinate conversion step of converting a read position in the stored image according to the calculated correction amount, and reading out a pixel of the converted read position from the image stored in the memory, where the shifting amount storage unit stores information indicating a shifting amount in a sub-scanning direction of a pixel on the scanning line drawn on the image carrier with the beam from an ideal scanning line.

An image forming apparatus comprising:

• a shifting amount storage unit configured to store shifting amount information indicating a shifting amount in a sub-scanning direction of a scanning line drawn on an image carrier of an image forming unit from an ideal scanning line;
• a selecting unit configured to select a rotational speed of the image carrier from among a plurality of rotational speeds of the image carrier;
• a setting unit configured to set a size of a print medium;
• a calculation unit configured to calculate a correction amount in a sub-scanning direction of a pixel included in an image to be formed by the image forming unit, on the basis of the selected rotational speed, the set size of a print medium and the stored information, wherein the more the selected rotational speed, the greater a correction amount in a sub-scanning direction of a pixel included in the image is;
• a coordinate conversion unit configured to convert a coordinate of the image on the basis of the calculated correction amount;
• a transfer unit configured to transfer the converted image to the image forming unit.

A method of controlling an image forming apparatus, the method comprising:

• storing shifting amount information indicating a shifting amount in a sub-scanning direction of a scanning line drawn on an image carrier of an image forming unit from an ideal scanning line;
• selecting a rotational speed of the image carrier from among a plurality of rotational speeds of the image carrier;
• setting a size of a print medium;
• calculating a correction amount in a sub-scanning direction of a pixel included in an image to be formed by the image forming unit, on the basis of the selected rotational speed, the set size of a print medium and the stored information, wherein the more the selected rotational speed, the greater a correction amount in a sub-scanning direction of a pixel included in the image is;
• a coordinate conversion step of converting a coordinate of the image on the basis of the calculated correction amount
• a transfer unit configured to transfer the converted image to the image forming unit.

An image processing apparatus comprising:

• an image storage unit configured to store an image into a memory;
• an information storage unit configured to store information representing a shifting amount in a sub scanning direction of a scanning line on an image carrier in an image forming unit drawn with a beam from an ideal scanning line;
• a setting unit configured to set a rotation speed of the image carrier;
• a calculation unit configured to, on the basis of a position in a main scanning direction of a pixel included in the stored image, calculate as a correction amount in the sub-scanning direction a sum of
• (i) a shifting amount in the sub-scanning direction at the position in the main-scanning direction, determined on the basis of the set rotational speed, and
• (ii) a shifting amount in the sub-scanning direction at the position in the main-scanning direction, determined on the basis of the stored information;
• and
• a conversion unit configure to convert, on the basis of the correction amount, a position in the sub-canning direction of the pixel included in the stored image.

A method of controlling an image forming apparatus, the method comprising:

• storing an image into a memory;
• storing information representing a shifting amount in a sub scanning direction of a scanning line on an image carrier in an image forming unit drawn with a beam from an ideal scanning line;
• setting a rotation speed of the image carrier;
• calculating, on the basis of a position in a main scanning direction of a pixel included in the stored image, as a correction amount in the sub-scanning direction, a sum of
• (i) a shifting amount in the sub-scanning direction at the position in the main-scanning direction, determined on the basis of the set rotational speed, and
• (ii) a shifting amount in the sub-scanning direction at the position in the main-scanning direction, determined on the basis of the stored information;
• and
• converting, on the basis of the correction amount, a position in the sub-canning direction of the pixel included in the stored image.

An image forming apparatus including a first storage unit configure to store an image including a plurality of pixels, a second storage unit configured to store a shifting amount in the sub-scanning direction corresponding to a coordinate position in a main-scanning direction for scanning on an image carrier, and a reading unit configured to read a pixel of an image stored in the first storage unit at a coordinate position shifted in the sub-scanning direction on the basis of the shifting amount stored in the second storage unit, the apparatus further comprising:

• a determination unit configured to determine whether a pixel belongs to a line image or a halftone image;
• a tone correction unit configured to, in a case where the determination unit determines that the pixel belongs to a line image, perform a tone correction processing for correcting the pixel by calculating a weighting average of the pixel and a pixel on a neighboring main-scanning line using weighting coefficients based on the stored shifting amount, and, in a case where the determination unit determines that the pixel belongs to a halftone image, not perform the tone correction processing to the pixel;
• and
• an image forming unit configured to convert an image from the tone correction unit into signals for exposing, and visualize using a color former a latent image generated by exposing in accordance with the converted signals.

An image forming method using a first storage unit configured to store an image including a plurality of pixels and a second storage unit configured to store a shifting amount in a sub-scanning direction corresponding to a coordinate position in a main-scanning direction for scanning on an image carrier, comprising:

• reading a pixel of an image stored in the first storage unit at a coordinate position shifted in the sub-scanning direction on the basis of the stored shifting amount;
• determining whether a pixel belongs to a line image or a halftone image;
• performing, in a case where the determination indicates that the pixel belongs to a line image, a tone correction processing for correcting the pixel by calculating a weighting average of the pixel and a pixel on a neighboring main-scanning line using weighting coefficients based on the stored shifting amount, and not performing, in a case where the determination indicates that the pixel belongs to a halftone image, the tone correction processing to the pixel;
• converting an image on which the reading and the tone correction processing have been performed into signals for exposing;
• visualizing using a color former a latent image generated by exposing in accordance with the converted signals.