Quantification of motion quality effect on image quality

• US 6,522,430 B1
• Filed: 11/29/1999
• Issued: 02/18/2003
• Est. Priority Date: 11/29/1999
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Dalal, Edul N., Rasmussen, D. Rene
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Lu, Tom Y.
• Application Number:
  US09/450,184
• Time in Patent Office: 1,177 Days
• Field of Search: 358/296, 358/496-497, 358/406, 358/504, 355/208, 382/141, 382/312
• US Class Current: 358/406
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00015 Reproducing apparatus
• CPC Class Codes: H04N 1/00023 Colour systems
• CPC Class Codes: H04N 1/00031 Testing, i.e. determining the result of a trial H04N1/00029 takes precedence; using test signals for transmission mode changing H04N2201/33371
• CPC Class Codes: H04N 1/00045 using a reference pattern designed for the purpose, e.g. a test chart
• CPC Class Codes: H04N 1/00053 out of service, i.e. outside of normal operation
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 1/00079 remotely

Abstract

An image quality analysis system is provided that allows highly accurate measurements of motion quality defects. The motion quality analysis process relies only on relative measurements, which can be performed sufficiently accurately with standard input scanners. The technique can therefore be incorporated in the image path of a copier or multi-function printer being tested to allow on-the-fly motion quality correction without the need for expensive, high precision measuring equipment. The system includes one or more digital test patterns provided in hardcopy form for providing one or more hardcopy test images, an input scanner that can scan the hard copy test image to form a digital raster image, and an image quality analysis module that receives information about the position of the digital raster image and produces test results relevant to determination of image quality analysis, particularly motion quality defects. The method is accurate and robust using relatively low-resolution CCD-based flat bed scanners, even in spite of their long-range positional errors.

Claims

1. A method of performing image quality analysis on an image output device having an output station that generates a hardcopy color image output from an input image, the method comprising:

providing the image output device with at least one pre-printed hardcopy test pattern page having pre-printed marks that have been accurately measured in advance;

generating a hardcopy image output from the image output device using a digital test pattern as an input image having marks that match those on the pre-printed hardcopy test pattern page, the hardcopy image being generated on one of the at least one pre-printed test pattern page;

scanning the hardcopy image to form a digital raster image; and

performing image quality analysis on the digital raster image, including determination of motion quality defects based on a comparison of the accurately measured pre-printed marks and the generated hardcopy image corresponding to the digital test pattern.

2. The method of claim 1, wherein the step of scanning uses a scanner of the image output device.

3. The method of claim 2, wherein the step of performing image quality analysis includes:

determining relative offsets between the pre-printed marks and the hardcopy image; and

converting the offsets to positions on the page using the pre-measured exact positions of the pre-printed marks to extract quantitative information on motion quality errors.

4. The method of claim 1, wherein the image output device is a copier.

5. The method of claim 1, further comprising a step of measuring the pre-printed marks on the hardcopy test pattern page using a scanning microdensitometer.

6. The method of claim 1, wherein the step of scanning uses a flat bed scanner.

7. The method of claim 1, wherein the pre-printed marks are spaced by a predetermined uniform or variable spacing and cover substantially the entire page.

8. The method of claim 7, wherein the uniform spacing is about 10 mm.

9. An image quality analysis system for performing image quality analysis on an image output device, the system comprising:

at least one preprinted test page having a plurality of accurately measured marks extending over a substantial part of the page;

a digital test pattern with marks matching those on the preprinted test page;

an output station of the image output device that generates a hardcopy image corresponding to the digital test pattern, the hardcopy image being output on the at least one pre-printed test page;

a scanner that forms a digital raster image from the hardcopy image output from the image output device; and

an image quality analysis module that performs image quality analysis on the digital raster image, including determination of motion quality defects based on a comparison of the accurately measured pre-printed marks and the generated hardcopy image corresponding to the digital test pattern.

10. The system of claim 9, wherein the scanner is part of the image output device.

11. The system of claim 10, wherein the image quality analysis module includes means for determining relative offsets between the pre-printed marks and the hardcopy image and means for converting the offsets to positions on the page using the pre-measured exact positions of the pre-printed marks to extract quantitative information on motion quality errors.

12. The system of claim 9, wherein the image output device is a copier.

13. The system of claim 9, wherein the scanner is an independent flat bed scanner.

14. The system of claim 9, wherein the accurately measured marks are spaced by a predetermined uniform or variable spacing and cover substantially the entire page.

15. The system of claim 14, wherein the spacing is uniform and about 10 mm.