Image processing apparatus and method evaluating print quality based on density difference data

1. An information processing apparatus comprising:

a memory storing instructions; and

a processor that implements the instructions to execute a plurality of tasks, including:

an obtaining task that obtains data of a reference image indicating a target of printing output to be performed by a printing apparatus and data of a printed image printed by the printing apparatus; and

an evaluating task that evaluates quality of the printed image based on:

a local image density difference between the reference image and the printed image; and

a global image density difference between the reference image and the printed image.

2. The apparatus according to claim 1 , wherein:

the local image density difference is between a specific pixel position In the reference image and a specific pixel position in the printed image, and

the evaluating task, in evaluating the quality of the printed image based on the local image density difference, compares between a partial region centered around the specific pixel position in the reference image, and a partial region centered around the specific pixel position in the printed image.

3. The apparatus according to claim 1 , wherein the:

the local image density difference is between a specific pixel position in the reference image and a specific pixel position in the printed image, and

the evaluating task, in evaluating the quality of the printed image based on the local image density difference, compares between a pixel value distribution in a partial region centered around the specific pixel position in the reference image, and a pixel value distribution in a partial region centered around the specific pixel position in the printed image.

4. The apparatus according to claim 1 , wherein the local image density difference is between the reference image in which an influence of the global image density difference is reduced and the printed image.

5. The apparatus according to claim 4 , wherein the evaluating task evaluates that the quality of the printed image has a defect, in a state where a smaller one of:

the local image density difference between the reference image in which an influence of the global image density difference is reduced and the printed image; or

the local image density difference between the reference image and the printed image in corresponding pixel positions, is not less than a first threshold and has a predetermined shape.

6. The apparatus according to claim 4 , wherein the evaluating task evaluates that the quality of the printed image has a defect, in a state where a region formed by pixels in pixel positions where a smaller one of:

the local image density difference between the reference image in which an influence of the global image density difference is reduced and the printed image; or

the local image density difference between the reference image and the printed image in corresponding pixel positions, is not less than a first threshold and has a predetermined shape.

7. The apparatus according to claim 1 , wherein:

the plurality of tasks include a correcting task that:

determines whether the global image density difference satisfies a predetermined condition; and

corrects the reference image based on the printed image in a state where the global image density difference satisfies the predetermined condition, and the evaluating task uses the corrected reference image to evaluate quality of another printed image.

8. The apparatus according to claim 7 , wherein the correcting task corrects the reference image in a state where the global image density difference between corresponding pixel positions in the printed image and the reference image is not more than a first threshold in all pixel positions of the printed image.

9. The apparatus according to claim 8 , wherein the correcting task corrects the reference image in a state where the global image density difference between corresponding pixel positions in the printed image and the reference image is not less than a second threshold in all pixel positions of the printed image.

10. The apparatus according to claim 7 , wherein the correcting task, in determining whether the global image density difference satisfies the predetermined condition, determines whether a distribution of image density differences between corresponding pixel positions in the printed image and the reference image satisfies the predetermined condition.

11. The apparatus according to claim 10 , wherein the correcting task corrects the reference image in a state where, in all pixel positions of the printed image:

the global image density difference between corresponding pixel positions in the printed image and the reference image has a same sign, and

a maximum value, a mean value, and a variance value of the global image density difference between corresponding pixel positions of the printed image and the reference image in each pixel position of the printed image are respectively not more than a first threshold, not less than a second threshold, and not more than a third threshold.

12. The apparatus according to claim 7 , wherein the reference image is corrected by updating the reference image to the printed image.

13. The apparatus according to claim 1 , wherein the plurality of tasks include a notification task that notifies a user of the global image density difference.

14. The apparatus according to claim 1 , wherein the global image density difference is produced in accordance with an elapsed time or the number of times of output from the printing apparatus.

15. The apparatus according to claim 1 , wherein the obtaining task obtains:

an output from the printing apparatus at a first time as the reference image; and

as the printed image, an output from the printing apparatus at a second time at which the printing apparatus keeps operating from the first time.

16. In information processing apparatus comprising:

a memory storing instructions; and

a processor that implements the instructions to:

obtain data of a reference image indicating a target of printing output to be performed by a printing apparatus;

obtain data of a printed image by reading an image printed by the printing apparatus;

generate difference data using:

a first image density difference between:

a pixel in a position of a pixel of interest in the reference image; and

a pixel in the position of a pixel of interest in the printed image; and

a third image density difference obtained by subtracting, from the first image density difference, a second image density difference between:

a region containing the pixel in the position of the pixel of interest in the reference image; and

a region containing the pixel in the position of the pixel of interest in the printed image; and

evaluate quality of the printed image based on the difference data.

17. An information processing method comprising:

obtaining data of a reference image indicating a target of printing output to be performed by a printing apparatus and data of a printed image printed by the printing apparatus; and

evaluating quality of the printed image based on:

a local image density difference between the reference image and the printed image; and

a global image density difference between the reference image and the printed image.

18. An information processing method comprising:

obtaining data of a reference image indicating a target of printing output to be performed by a printing apparatus;

obtaining data of a printed image by reading an image printed by the printing apparatus;

generating difference data using:

a first image density difference between:

a pixel in a position of a pixel of interest in the reference image:, and

a pixel in the position of a pixel of interest in the printed image; and

a third image density difference obtained by subtracting, from the first image density difference, a second image density difference between:

a region containing the pixel in the position of the pixel of interest in the reference image; and

a region containing the pixel in the position of the pixel of interest in the printed image; and

evaluating quality of the printed image based on the difference data.