Image forming apparatus

1. An image forming apparatus, comprising:

an image carrier that holds a toner pattern;

a memory device in which toner pattern data has been stored;

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

a controller that performs development of toner patterns based on the toner pattern data corresponding to a first halftoning method and a second halftoning method, and identifies respective toner density values of patch images contained in each of the toner patterns from output of the sensor, the patch images corresponding to grades in a gradation respectively;

wherein one of the toner patterns contains first patch images for the first halftoning method, and another of the toner patterns contains second patch images for the second halftoning; and the controller performs development of only one out of both a first patch image which is one of the first patch images and a second patch image which is one of the second patch images and identifies toner density values of both the first patch image and the second patch image from output of the sensor for the only one out of both the first patch image and the second patch image if an absolute value of a difference between the number of dots in the first patch image and the number of dots in the second patch image is equal to or less than a predetermined value and an absolute value of a difference between the number of dot-level edges in the first patch image and the number of dot-level edges in the second patch image is equal to or less than a predetermined value.

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

the controller performs development of only one out of both the first patch image and the second patch image and identifies toner density values of both the first patch image and the second patch image from output of the sensor for the only one out of both the first patch image and the second patch image if the difference between the number of dots in the first patch image and the number of dots in the second patch image is equal to zero and an absolute value of a difference between the number of dot-level edges in the first patch image and the number of dot-level edges in the second patch image is equal to or less than a predetermined value.

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

the controller performs development of only one out of both the first patch image and the second patch image and identifies toner density values of both the first patch image and the second patch image from output of the sensor for the only one out of both the first patch image and the second patch image if the difference between the number of dots in the first patch image and the number of dots in the second patch image is equal to zero and the difference between the number of dot-level edges in the first patch image and the number of dot-level edges in the second patch image is equal to zero.

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

the toner pattern data is threshold-converted data of the toner patterns that have the first patch images and the second patch images except either the first patch image not developed or the second patch image not developed, and the controller performs development of the toner patterns based on the toner pattern data.

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

the toner pattern data is threshold-converted data of a partial image, the partial image is a part of a base pattern image with a predetermined size and does not include any side parts of the base pattern image, and the controller generates a patch image by arranging the partial image repeatedly, and performs the development by using the generated patch image.

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

the first halftoning method is a screen method, and the second halftoning method is an error diffusion method.

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

a photoconductor; and

a development device that develops the toner patterns on the photoconductor;

wherein the image carrier is an intermediate transfer member onto which the toner patterns are transferred from the photoconductor, and the controller performs development of the toner patterns on the photoconductor by controlling the development device.

8. An image forming apparatus, comprising:

an image carrier that holds a toner pattern;

a memory device in which toner pattern data has been stored;

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

a controller that performs development of toner patterns based on the toner pattern data corresponding to a first halftoning method and a second halftoning method, and identifies respective toner density values of patch images contained in each of the toner patterns from output of the sensor, the patch images corresponding to grades in a gradation respectively;

wherein one of the toner patterns contains first patch images for the first halftoning method, another of the toner patterns contains second patch images for the second halftoning, a first patch image which is one of the first patch images corresponds to a grade equal to or higher than a predetermined grade in the gradation, and a second patch image which is one of the second patch images corresponds to a grade equal to or higher than a predetermined grade in the gradation; and the controller performs development of only one out of both the first patch image and the second patch image and identifies toner density values of both the first patch image and the second patch image from output of the sensor for said only one out of both the first patch image and the second patch image if an absolute value of a difference between the number of dots in the first patch image and the number of dots in the second patch image is equal to or less than a predetermined value; wherein the toner pattern data is threshold-converted data of a partial image, the partial image is a part of a base pattern image with a predetermined size and does not include any side parts of the base pattern image, and the controller generates a patch image by arranging the partial image repeatedly, and performs development by using the generated patch image.

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

the toner pattern data is threshold-converted data of the toner patterns that have the first patch images and the second patch images except either the first patch image not developed or the second patch image not developed, and the controller performs development of the toner patterns based on the toner pattern data.

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

the first halftoning method is a screen method, and the second halftoning method is an error diffusion method.

11. The image forming apparatus according to claim 8 , further comprising:

a photoconductor; and

a development device that develops the toner patterns on the photoconductor;

wherein the image carrier is an intermediate transfer member onto which the toner patterns are transferred from the photoconductor, and the controller performs development of the toner patterns on the photoconductor by controlling the development device.

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

a photoconductor; and

a development device that develops the toner patterns on the photoconductor;

wherein the image carrier is an intermediate transfer member onto which the toner patterns are transferred from the photoconductor, and the controller performs development of the toner patterns on the photoconductor by controlling the development device.

13. An image forming apparatus, comprising:

an image carrier that holds a toner pattern;

a memory device in which toner pattern data has been stored;

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

a controller that performs development of toner patterns based on the toner pattern data corresponding to a first halftoning method and a second halftoning method, and identifies respective toner density values of patch images contained in each of the toner patterns from output of the sensor, the patch images corresponding to grades in a gradation respectively;

wherein one of the toner patterns contains first patch images for the first halftoning method, another of the toner patterns contains second patch images for the second halftoning, a first patch image which is one of the first patch images corresponds to a grade equal to or higher than a predetermined grade in the gradation, and a second patch image which is one of the second patch images corresponds to a grade equal to or higher than a predetermined grade in the gradation; and the controller performs development of only one out of both the first patch image and the second patch image and identifies toner density values of both the first patch image and the second patch image from output of the sensor for said only one out of both the first patch image and the second patch image if the difference between the number of dots in the first patch image and the number of dots in the second patch image is equal to zero.

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

the toner pattern data is threshold-converted data of the toner patterns that have the first patch images and the second patch images except either the first patch image not developed or the second patch image not developed, and the controller performs development of the toner patterns based on the toner pattern data.

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

the first halftoning method is a screen method, and the second halftoning method is an error diffusion method.