Image forming apparatus

1. An image forming apparatus forming an image by using an electronic photography process, comprising:

an image carrier capable of holding a toner pattern;

a memory device in which toner pattern data is stored;

a sensor that puts detection light onto the image carrier and detects reflection light from the image carrier; and

a control unit that forms the toner pattern based on the toner pattern data and identifies a toner density of the toner pattern from output of the sensor;

wherein the toner pattern data is threshold conversion data of a partial image, the partial image is a part of a base pattern image with a predetermined size and does not contain any sides of the base pattern image, and the base pattern image is an image generated in a threshold conversion method that performs single or multiple threshold conversion by sequentially calculating a converted pixel value from original values of adjacent pixels; and the control unit generates an image of the toner pattern by arranging the partial image of the toner pattern data repeatedly.

2. The image forming apparatus according to claim 1 , wherein:

the toner pattern data is threshold conversion data of a partial image, the partial image is a part of a base pattern image with a predetermined size and does not contain any sides of the base pattern image, and the base pattern image is an image generated by an error diffusion method.

3. The image forming apparatus according to claim 2 , further comprising a RAM;

wherein the control unit stores the toner pattern data in the RAM, reads the toner pattern data from the RAM repeatedly to generate the image of the toner pattern.

4. The image forming apparatus according to claim 2 , wherein:

the partial image is smaller than a beam spot formed by the detection light on the image carrier.

5. The image forming apparatus according to claim 2 , wherein:

the partial image has pixels of which the number is sufficient to depict a predetermined number of gradation levels.

6. The image forming apparatus according to claim 2 , wherein:

the toner pattern data is single-threshold conversion data.

7. The image forming apparatus according to claim 2 , wherein:

a photoconductor; and

a developing device that develops the toner pattern on the photoconductor;

wherein the image carrier is an intermediate transferer on which the toner pattern is transferred from the photoconductor, and the control unit controls the developing device to develop the toner pattern on the photoconductor.

8. The image forming apparatus according to claim 1 , wherein:

the partial image is an image chosen from candidate partial images in the base pattern image so that an image characteristic of an image generated by arranging the chosen image repeatedly to be with the predetermined size is closest to an image characteristic of the base pattern image.

9. The image forming apparatus according to claim 8 , wherein:

the partial image is an image chosen from candidate partial images in the base pattern image so that the number of dots in an image generated by arranging the chosen image repeatedly to be with the predetermined size is closest to the number of dots in the base pattern image.

10. The image forming apparatus according to claim 8 , wherein:

the partial image is an image chosen from candidate partial images in the base pattern image so that the number of dot-sized edges in an image generated by arranging the chosen image repeatedly to be with the predetermined size is closest to the number of dot-sized edges in the base pattern image.

11. The image forming apparatus according to claim 8 , further comprising a RAM;

wherein the control unit stores the toner pattern data in the RAM, reads the toner pattern data from the RAM repeatedly to generate the image of the toner pattern.

12. The image forming apparatus according to claim 8 , wherein:

the partial image is smaller than a beam spot formed by the detection light on the image carrier.

13. The image forming apparatus according to claim 8 , wherein:

the partial image has pixels of which the number is sufficient to depict a predetermined number of gradation levels.

14. The image forming apparatus according to claim 8 , wherein:

the toner pattern data is single-threshold conversion data.

15. The image forming apparatus according to claim 8 , wherein:

a photoconductor; and

a developing device that develops the toner pattern on the photoconductor;

wherein the image carrier is an intermediate transferer on which the toner pattern is transferred from the photoconductor, and the control unit controls the developing device to develop the toner pattern on the photoconductor.

16. The image forming apparatus according to claim 1 , further comprising a RAM;

wherein the control unit stores the toner pattern data in the RAM, reads the toner pattern data from the RAM repeatedly to generate the image of the toner pattern.

17. The image forming apparatus according to claim 1 , wherein:

the partial image is smaller than a beam spot formed by the detection light on the image carrier.

18. The image forming apparatus according to claim 1 , wherein:

the partial image has pixels of which the number is sufficient to depict a predetermined number of gradation levels.

19. The image forming apparatus according to claim 1 , wherein:

the toner pattern data is single-threshold conversion data.

20. The image forming apparatus according to claim 1 , further comprising:

a photoconductor; and

a developing device that develops the toner pattern on the photoconductor;

wherein the image carrier is an intermediate transferer on which the toner pattern is transferred from the photoconductor, and the control unit controls the developing device to develop the toner pattern on the photoconductor.