Image forming apparatus and method for color registration correction

1. An image forming apparatus comprising:

an image former including a plurality of photosensitive drums to print, on a printing paper, a plurality of lines that are oriented perpendicular to a main scanning direction of the image former to be arranged at predetermined intervals along the main scanning direction,

each line of the plurality of lines including a plurality of colored sub-lines oriented perpendicular to the main scanning direction to be formed along a sub-scanning direction of the image former by corresponding photosensitive drums, and

at least two sub-lines among the plurality of sub-lines printed using a different respective one of the plurality of photosensitive drums;

a scanner to scan the printing paper, on which the plurality of lines is printed, to obtain a scanned image of the plurality of lines; and

at least one processor to perform color registration correction using the scanned image.

2. The image forming apparatus as claimed in claim 1 , wherein the at least one processor performs the registration correction for the plurality of photosensitive drums for a plurality of positions along the main scanning direction that respectively correspond to the plurality of lines, by using the scanned image.

3. The image forming apparatus as claimed in claim 1 , wherein for each of the plurality of lines,

the respective sub-lines include first to fifth sub-lines sequentially arranged along the sub-scanning direction, and

the image former prints the first and fifth sub-lines on the printing paper using a same photosensitive drum among the plurality of photosensitive drums.

4. The image forming apparatus as claimed in claim 3 , wherein the at least one processor:

calculates skew values of the plurality of lines using the first and fifth sub-lines, and

performs the registration correction for the plurality of photosensitive drums based on the calculated skew values.

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

the plurality of photosensitive drums includes a photosensitive drum that corresponds to a black color, and

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

6. The image forming apparatus as claimed in claim 5 , wherein the at least one processor:

detects errors in the sub-lines based on the first and fifth sub-lines, and

based on the detected errors, corrects irradiation positions of photo sensors that correspond to C, M, and Y colors, respectively, for a plurality of positions along the main scanning direction that correspond to the plurality of lines.

7. The image forming apparatus as claimed in claim 1 , wherein the image former 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.

8. The image forming apparatus as claimed in claim 1 , wherein the plurality of lines are 49 lines.

9. The image forming apparatus as claimed in claim 1 , wherein a number of the plurality of lines is determined based on a quantity of a unit in which timing of an exposure device of the image forming apparatus is adjustable, and based on a sampling number for each of the units.

10. The image forming apparatus as claimed in claim 9 , wherein the sampling number is a natural number in a range of 1 to 8.

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

12. The image forming apparatus as claimed in claim 1 , wherein the image former prints at least one of an English sentence, a figure, and a barcode, which indicates an identity the image forming apparatus, together with the plurality of lines.

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

printing, on a printing paper by using a plurality of photosensitive drums of an image former, a plurality of lines that are oriented perpendicular to a main scanning direction of the image former to be arranged at predetermined intervals along the main scanning direction,

each line of the plurality of lines including a plurality of colored sub-lines oriented perpendicular to the main scanning direction to be formed along a sub-scanning direction of the image former by corresponding photosensitive drums, and

at least two sub-lines among the plurality of sub-lines printed using a different respective one of the plurality of photosensitive drums;

scanning the printing paper, on which the plurality of lines is printed, to obtain a scanned image of the plurality of lines; and

performing color registration correction using the scanned image.

14. The method as claimed in claim 13 , wherein the performing the correction performs the registration correction for the plurality of photosensitive drums for a plurality of positions along the main scanning direction that respectively correspond to the plurality of lines, by using the scanned image.

15. The method as claimed in claim 13 , wherein for each of the plurality of lines,

the respective plurality of sub-lines includes first to fifth sub-lines sequentially arranged along the sub-scanning direction, and

the printing prints the first and fifth sub-lines on the printing paper using a same photosensitive drum among the plurality of photosensitive drums.

16. The method as claimed in claim 15 , wherein the performing the registration correction comprises:

calculating skew values of the plurality of lines using the first and fifth sub-lines, and

performing the registration correction for the different photosensitive drums based on the calculated skew values.

17. The method as claimed in claim 15 , wherein

the plurality of photosensitive drums includes a photosensitive drum that corresponds to a black color, and

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

18. The method as claimed in claim 17 , wherein the performing the registration correction comprises:

detecting errors in the sub-lines based on the first and fifth sub-lines, and

based on the detected errors, correcting irradiation positions of photo sensors that correspond to C, M, and Y colors, respectively, for a plurality of positions in the main scanning direction that correspond to the plurality of lines.

19. The method as claimed in claim 13 , 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.

20. The method as claimed in claim 13 , wherein a number of the plurality of lines is determined based on a quantity of a unit in which timing of an exposure device used to print the plurality of lines is adjustable, and based on a sampling number for each of the units.