Method for compensating for color variations across a printed page using multiple-pass printing
A method for compensating for color variations introduced by printer hardware limitations and other factors is described. First, for each printer model or each individual printer, the extent of color variation throughout a printed page is determined. Based on this determination, each page is partitioned into a plurality of image areas. Then, in an actual printing process, the page of image is printed in a multi-pass process where each image area is printed in a separate pass. The digital image data is shifted and/or rotated for each pass, and the paper is shifted and/or rotated correspondingly, so that the different image areas printed in different passes form a complete image on the final printed page. From the standpoint of the pointer hardware, all passes involve printing the same area of a physical page, resulting in reduced color variation across the page.
1. A method for printing a page of image using a printer, comprising:
(a) printing a page of engine test chart having a paper size using the printer;
(b) measuring the printed engine test chart to obtain color values at different locations of the page;
(c) based on the measured color values and without regard to image attributes of any image to be printed later, determining a page partition for dividing all pages of images to be printed later which have the paper size into two or more image areas;
(d) storing the page partition in the printer;
repeating steps (a) to (d) for additional paper sizes;
after steps (a) to (d),
(e) receiving a page of digital image data to be printed;
(f) retrieving stored page partition information for a plurality of paper sizes;
(g) detecting a paper size of the page of image to be printed;
(h) dividing the page of image to be printed into two or more image areas based on the detected paper size and the retrieved page partition information; and
(i) printing the two or more image areas on a medium, including:
(i1) printing a first image area on a medium;
(i2) after step (i1), rotating and/or shifting the digital image data so that a second image area is located in a same area on the page as the first image area is originally located;
(i3) rotating and/or shifting the medium corresponding to the rotation and/or shift of the digital image data in step (i2);
(i4) after the rotating and/or shifting steps of (i2) and (i3), printing the second image area which has been rotated and/or shifted by step (i2) on the medium which has been rotated and/or shifted by step (i3); and
(i5) repeating steps (i2) to (i4) for any additional image areas.
2. The method of claim 1 , wherein step (c) includes calculating an amount of color variation for a plurality of locations on the page.
3. The method of claim 1 , wherein steps (a) through (c) are performed for a full printable area of the printer.
4. The method of claim 1 , wherein in step (h), the page of image is divided into two image areas along a medium feeding direction of the printer, wherein step (i2) includes shifting the image in the medium feeding direction by half of the page, and wherein step (i3) includes shifting the medium in the medium feeding direction by half of the page.
5. A printer, comprising:
a print engine including a document feeding path; and
a controller for processing digital image data to be printed and controlling the print engine, the controller including a processor and a memory;
wherein the memory stores page partition information which specifies, for each of a plurality of paper sizes, a partition of all pages of images to be printed which have the paper size into two or more image areas, the partition for each paper size having been obtained by printing a page of engine test chart having the paper size using the printer, measuring the printed engine test chart to obtain color values at different locations of the page of engine test chart, and determining the partition based on the measured color values and without regard to image attributes of any image to be printed, and
wherein the controller is programmed to control the print engine to carry out a printing process which includes:
(a) receiving a page of digital image data to be printed;
(b) retrieving page partition information stored in the memory;
(c) detecting a paper size of the page of image to be printed;
(d) dividing the page of image to be printed into two or more image areas based on the detected paper size and the retrieved page partition information; and
(e) printing the two or more image areas on a medium, including:
(e1) printing a first image area on a medium;
(e2) after step (e1), rotating and/or shifting the digital image data so that a second image area is located in a same area on the page as the first image area is originally located;
(e3) rotating and/or shifting the medium corresponding to the rotation and/or shift of the digital image data in step (e2);
(e4) after the rotating and/or shifting steps of (e2) and (e3), printing the second image area which has been rotated and/or shifted by step (e2) on the medium which has been rotated and/or shifted by step (e3); and
(e5) repeating steps (e2) to (e4) for any additional image areas.
6. The printer of claim 5 , wherein in step (d), the page of image is divided into two image areas along a medium feeding direction of the printer, wherein step (e2) includes shifting the image in the medium feeding direction by half of the page, and wherein step (e5) includes shifting the medium in the medium feeding direction by half of the page.
7. The method of claim 1 , wherein the page partition defines partial areas of multiple prints in a multiple-pass process.
8. The method of claim 1 , wherein in step (c), the page partition divides the page into two or more image areas in a paper feeding direction, or divides the page into two or more image areas in a direction perpendicular to the paper feeding direction.