Image forming apparatus and method for color registration correction

1. An image forming apparatus comprising:

a processor to control, in response to a determined condition, an image former to print on a recording medium by at least two photosensitive drums among a plurality of photosensitive drums respectively corresponding to a plurality of colors, a color chart of a plurality of vertical lines in a sub-scanning direction to a main scanning direction of the recording medium and to be arranged at intervals along the main scanning direction,

a vertical line of the plurality of vertical lines including at east two colored sub-lines to be formed by the at least two photosensitive drums; and

the processor to perform a correction due to non-linear color registrations in the main scanning direction using an image of the color chart,

wherein the image former prints horizontal lines that are respectively in contact with upper and lower portions of the plurality of vertical lines and are vertical to the sub-scanning direction, and

the processor is to,

calculate, according to the horizontal lines, a skew value of the vertical line using the first and fifth colored sub-lines, and

perform the correction in the non-linear color registrations for the at least two photosensitive drums based on the calculated skew value.

2. The image forming apparatus as claimed in claim 1 , wherein the processor is to perform, using the image, the correction in the non-linear color registrations for at least two photosensitive drums for a plurality of positions along the main scanning direction that respectively correspond to the plurality of vertical lines.

3. The image forming apparatus as claimed in claim 1 , wherein,

the at least two colored sub-lines include first to fifth colored sub-lines, and

the photosensitive drums print the first and fifth colored sub-lines on the recording medium using same photosensitive drum from among the plurality of photosensitive drums.

4. The image forming apparatus as claimed in claim 3 , wherein a processor is to:

calculate a skew value of the vertical line using the first and fifth colored sub-lines, and

correct irradiation positions of photo sensors that respectively correspond to photosensitive drums, among the plurality of photosensitive drums, corresponding to the C, M, and colors, for a plurality of positions along the main scanning direction that correspond to the plurality of vertical lines, to perform the color registration correction for the at least two photosensitive drums based on the calculated skew value.

5. The image forming apparatus as claimed in claim 4 , wherein

the same photosensitive drum corresponds to a black color, and

the first and fifth colored sub-lines are both formed by the same photosensitive tart that corresponds to the black color.

6. The image forming apparatus as claimed in claim 1 , further comprising an exposure device, wherein,

the processor is to detect errors in the colored sub-lines corresponding to C, M and Y colors, and

the processor is and/or the exposure device is, based on the detected errors, to correct irradiation positions of and/or pixel widths for photo sensors that respectively correspond to photosensitive drums, among the plurality of photosensitive drums, corresponding to the C, M, and Y colors, for a plurality of positions along the main scanning direction that correspond to the plurality of vertical lines.

7. The image forming apparatus as claimed in claim 1 , further comprising a scanner to scan the recording medium to input a scanned image of the color chart.

8. The image forming apparatus as claimed in claim 1 , wherein a number of the plurality of vertical lines is determined based on adjustability by a quantity of a unit of a polygon mirror of an exposure device by which timing of the exposure device is adjustable, and based on a sampling number for the unit.

9. The image forming apparatus as claimed in claim 8 , wherein the plurality of vertical lines in range of 2 to 73 vertical lines when the sampling number is a natural number in a range of 1 to 8.

10. The image forming apparatus as claimed in claim 1 , wherein the image former prints a shape at a position that is spaced apart from the plurality of vertical lines.

11. The image forming apparatus as claimed in claim 1 , wherein the image former prints an English sentence, a figure, ands or a barcode, to indicate an identity the image forming apparatus, together with the plurality of vertical lines.

12. A method for color registration by an image forming apparatus, the method comprising:

printing, on a recording medium by at least two photosensitive drums, among a plurality of photosensitive drums, respectively corresponding to a plurality of colors, a color chart of a plurality of vertical lines in a sub-scanning direction to a main scanning direction of the recording medium and to be arranged at intervals along the main scanning direction,

a vertical line of the plurality of vertical lines including at least two colored sub-lines to be formed by the at least two photosensitive drums among the photosensitive drums; and

perform a correction due to non-linear color registrations in the main scanning direction using an image of the color chart,

wherein the printing prints horizontal lines that are respectively in contact with upper and lower portions of the plurality of lines and are vertical to the sub-scanning direction, and the method further comprises:

by the processor,

calculating according to the horizontal lines, a skew value of the vertical line using the first and fifth colored sub-lines, and

performing the correction in the non-linear color registrations for the at least two photosensitive drums based on the calculated skew value.

13. The method as claimed in claim 12 , wherein the correction in the non-linear color registrations is performed, using the image, for the at least two photosensitive drums for a plurality of positions along the main scanning direction that respectively correspond to the plurality of vertical lines.

14. The method as claimed in claim 12 , wherein,

the at least two colored sub-lines include first to fifth colored sub-lines, and

the printing prints the first and fifth colored sub-lines on the recording medium using same photosensitive drum from among the plurality of photosensitive drums.

15. The method as claimed in claim 14 , wherein the color registration correction comprises:

calculating a skew value of the line using the first and fifth colored sub-lines, and

correcting irradiation positions of photo sensors that respectively correspond to photosensitive drums, among the plurality of photosensitive drums, corresponding to the C, M, and Y colors, for a plurality of positions along the main scanning direction that correspond to the plurality of vertical lines, to perform the color registration correction for the at least two photosensitive drum based on the calculated skew value.

16. The method as claimed in claim 15 , wherein

the same photosensitive drum corresponds to a black color, and

the first and fifth colored sub-lines are both formed by the same photosensitive drum that corresponds to the black color.

17. The method as claimed in claim 12 , wherein the correction in the non-linear color registrations comprises:

detecting errors in colored the sub-lines corresponding to C, M and Y colors, and

based on the detected errors, by the processor and/or an exposure device, correcting irradiation positions of and/or pixel widths for photo sensors that respectively correspond to photosensitive drums, among the plurality of photosensitive drums, corresponding to the C, M, and colors, for a plurality of positions in the main scanning direction that correspond to the plurality of vertical lines.

18. The method as claimed in claim 12 , wherein a number of the plurality of vertical lines is determined based on a adjustability by quantity of a unit of a polygon mirror of an exposure device by which timing of the exposure device is adjustable, and based on a sampling number for the unit,

wherein the plurality of vertical lines in range of 25 to 73 vertical lines when the sample number is a natural number in a range of 1 to 8.