Artifact reduction using a compensation image

1. A method for reducing artifacts in an electrophotographic printing system, comprising:

receiving a print job including image data for a set of pages to be printed with the electrophotographic printing system;

using the electrophotographic printing system to print a block of pages from the print job to provide corresponding printed pages, wherein the electrophotographic printing system includes a development subsystem that supplies toner used to form the printed pages;

analyzing the image data for the block of pages to determine an average toner usage rate;

defining an acceptable toner usage rate range, wherein the development subsystem supplies toner with an acceptable charge when the average toner usage rate is within the acceptable toner usage rate range;

if the determined average toner usage rate for the block of pages is outside the acceptable toner usage rate range:

determining image data for a compensation image; and

determining a number of compensation images to be printed;

wherein the image data for the compensation image and the number of compensation images are determined such that the average toner usage rate will be brought back into the acceptable toner usage rate range when the determined number of compensation images are printed using the electrophotographic printing system.

2. The method of claim 1 , further including using the electrophotographic printing system to print the specified number of compensation images if the determined average toner usage rate for the block of pages is outside the acceptable toner usage rate range.

3. The method of claim 2 , wherein the printed compensation images are directed into a waste receptacle.

4. The method of claim 2 , further including using the electrophotographic printing system to print additional pages from the print job to provide additional printed pages after the printing of the compensation images.

5. The method of claim 1 , wherein the compensation image is a uniform image.

6. The method of claim 5 , wherein the acceptable toner usage rate range is defined by a minimum acceptable toner usage rate and a maximum acceptable toner usage rate, and wherein if the determined average toner usage rate for the block of pages is greater than the maximum acceptable toner usage rate the compensation image is a blank image.

7. The method of claim 6 , wherein the number of compensation images is greater than or equal to:

K

m

=

⁢

⌈

S

⁡

(

V

¯

-

V

H

)

V

H

⌉

where K m is the minimum number of compensation images, S is the number of pages in the block of pages, V is the average toner usage rate for the block of pages, V H is the maximum acceptable toner usage rate, and ┌g┐ denotes a rounding up to the next integer operation.

8. The method of claim 5 , wherein the acceptable toner usage rate range is defined by a minimum acceptable toner usage rate and a maximum acceptable toner usage rate, and wherein if the determined average toner usage rate for the block of pages is less than the minimum acceptable toner usage rate the compensation image is a uniform image having a toner usage rate equal to the maximum acceptable toner usage rate.

9. The method of claim 8 , wherein the number of compensation images is greater than or equal to:

K

m

=

⁢

⌈

S

⁡

(

V

L

-

V

¯

)

(

V

H

-

V

L

)

⌉

where K m is the minimum number of compensation images, S is the number of pages in the block of pages, V is the average toner usage rate for the block of pages, V L is the minimum acceptable toner usage rate, V H is the maximum acceptable toner usage rate, and ┌g┐ denotes a rounding up to the next integer operation.

10. The method of claim 1 , wherein the step of determining an average toner usage rate includes computing a cross-track image profile P i (x) from the image data for each page in the block of pages:

P

i

(

x

)

=

1

N

y

⁢

∑

y

=

1

N

y

I

i

(

x

,

y

)

where I i (x,y) is the image data for the i th page, x and y are cross-track and in-track pixel positions, respectively, and N y is a number of image data pixels in an in-track dimension.

11. The method of claim 10 , wherein the average toner usage rate V h for color channel h is determined using the equation:

V

¯

h

=

1

N

x

⁢

S

⁢

∑

i

=

1

S

∑

x

=

1

N

x

P

h

i

(

x

)

where P h i (x) is the cross-track image profile for the i th page and the color channel h, N x is a number of image data pixels in a cross-track dimension and S is a number of pages in the block of pages.

12. The method of claim 10 , wherein the compensation image has a cross-track image profile which has an inverted shape relative to an average of the cross-track image profiles for the block of pages.

13. The method of claim 12 , wherein the cross-track image profile Ĉ(x) for the compensation image is determined by:

Ĉ ( x )= C ′( x )/ K

where K is the number of compensation images and C′(x) is shifted total compensation image profile given by:

Ĉ ′( x )= C ( x )−min[ C ( x )]

C(x) is a total compensation image profile given by:

C

⁡

(

x

)

=

∑

i

-

1

S

(

P

max

-

P

i

(

x

)

)

and P max is the maximum possible value for the cross-track image profiles P i (x).

14. The method of claim 13 , wherein the cross-track image profiles P i (x) are filtered with a low-pass filter before computing the total compensation image profile C(x).

15. The method of claim 13 , wherein the number of compensation images K is greater than or equal to a minimum number of compensation images K m given by:

K

m

=

⌈

max

[

C

′

(

x

)

]

P

max

⌉

where ┌g┐ denotes a rounding up to the next integer operation.

16. The method of claim 13 , the pages and the compensation images have a plurality of color channels h, and wherein a cross-track image profile Ĉ h (x) for each color channel of the compensation image is determined responsive to the cross-track image profiles P h i (x) for the corresponding color channel of the pages in the block of pages.

17. The method of claim 1 , wherein the pages have a plurality of color channels, and wherein a minimum number of compensation images is determined independently for each color channel, and wherein a number of compensation images is determined to be greater than or equal to the maximum value of the minimum number of compensation images for each color channel.

18. A method for reducing artifacts in an electrophotographic printing system, comprising:

receiving a print job including image data for a set of pages to be printed with the electrophotographic printing system;

designating a block of images from the print job to be printed using the electrophotographic printing system to provide corresponding printed pages, wherein the electrophotographic printing system includes a development subsystem that supplies toner used to form the printed pages;

analyzing the image data for the block of pages to determine an average toner usage rate;

defining an acceptable toner usage rate range, wherein the development subsystem supplies toner with an acceptable charge when the average toner usage rate is within the acceptable toner usage rate range;

if the determined average toner usage rate for the block of pages is outside the acceptable toner usage rate range:

determining image data for a compensation image; and

determining a number of compensation images to be printed;

wherein the image data for the compensation image and the number of compensation images are determined such that the average toner usage rate will be brought back into the acceptable toner usage rate range when the determined number of compensation images are printed using the electrophotographic printing system.