Method to obtain consistent image quality measurements from different image input devices

• US 6,597,473 B1
• Filed: 11/29/1999
• Issued: 07/22/2003
• 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: Rasmussen, D. Rene, Dalal, Edul N.
• Primary Examiner(s): Coles, Edward
• Assistant Examiner(s): Carter, Tia A
• Application Number:
  US09/450,183
• Time in Patent Office: 1,331 Days
• Field of Search: 358/500, 358/501, 358/518, 358/522, 358/1.9, 358/1.15, 358/406, 382/181, 382/112, 382/167, 382/287
• US Class Current: 358/1.9
• 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 1/00031 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 1/00061 using a remote apparatus H04N1/00066 takes precedence
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 1/00068 Calculating or estimating
• CPC Class Codes: H04N 1/00079 remotely

Abstract

An image quality analysis system is provided for image output devices, such as printers and copiers, that overcomes problems with differences in analysis results caused by use of different image input devices. This is achieved by computing a differential transfer function that makes subsequent analysis device independent. Moreover, the analysis is performed on an image that has been blurred to also reflect absolute image quality metrics as seen by a human observer. By determining the resolving characteristics of the input scanner, the scanned image can be processed, with little or no artifacts, to resemble the image as perceived by a human observer, while at the same time eliminating differences that would arise when using a scanner having a different spatial resolving power.

Claims

1. An image quality analysis system for an image output device that is input device independent, comprising:

a test pattern pertinent to image quality determination;

a scanner that scans a hardcopy test image, which has been generated by the output device based on the test pattern, to form a digital raster image, the scanner having a predetermined modulated transfer function (MTF);

means for blurring the digital raster image by a differential transfer function (DTF) corresponding to the modulation transfer function (MTF) divided by the visual transfer function (VTF) corresponding to a human visual system to form a blurred image; and

an image quality analysis module that receives the blurred image, distinguishes one or more test targets from the blurred image, and performs image quality analysis on the test targets to obtain results quantifying image quality,

wherein the results of the image quality analysis are scanner independent and the blurred image from which the image analysis was conducted corresponds to an image perceived by a human viewer when viewing the hardcopy test image.

2. The image quality analysis system of claim 1, wherein the image quality analysis module resides locally at a site of the image output device.

3. The image quality analysis system of claim 2, wherein the image output device is a copier that contains the scanner.

4. The image quality analysis system of claim 1, wherein the scanner and the image quality analysis module reside remote from the image output device.

5. The image quality analysis system of claim 1, wherein the test pattern is stored in memory at the image output device.

6. The image quality analysis system of claim 1, wherein the image output device is a copier having an input scanner section serving as the scanner and an output printer section, and the test pattern is in the form of a hardcopy printout that is subsequently scanned into the input scanner section and output as the hardcopy test image.

7. The image quality analysis system of claim 6, further comprising a communication module that connects the image quality analysis module to a remote facility.

8. The image quality analysis system of claim 7, wherein the results of the image quality analysis are forwarded to the remote facility through the communication module.

9. The image quality analysis system of claim 8, wherein the remote facility includes a diagnostic module that returns information pertinent to correcting any undesirable image quality test results.

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

generating a hardcopy test image from the image output device based on a predetermined test pattern pertinent to image quality determination;

scanning the hardcopy test image using a scanner to form a digital raster image;

determining a Modulation Transfer Function (MTF) for the scanner at different spatial frequencies;

determining a Visual Transfer Function (VTF) to take into account the sensitivity of a human visual system (HVS);

calculating a Differential Transfer Function (DTF) at each spatial frequency reflecting the difference between MTF and VTF;

transforming the scanned digital test image according to the DTF to degrade or blur the image to some extent from that achieved by the scanner such that this blurred image represents the image perceived by the human vision system (HVS); and

performing the image quality analysis based on the blurred image.

11. The method of claim 10, wherein the results of the image quality analysis are scanner independent and the blurred image from which the image analysis was conducted corresponds to an image perceived by a human viewer when viewing the hardcopy test image.

12. The method of claim 10, further comprising a step of sending a communication to a service facility indicating the results of the image quality analysis.

13. The method of claim 10, wherein the communication is a service call if the image quality results are less than desirable.

14. The method of claim 10, further comprising the steps of analyzing the results along with predetermined image output device operating parameters and communicating information to the image output device relevant to correcting the undesirable image quality.

15. The method of claim 10, wherein the image output device is a copier that contains the scanner.

16. The method of claim 10, wherein the method is automatically initiated by the copier at a predetermined time.

17. The method of claim 10, wherein the steps of scanning and analyzing are performed remote from the image output device.

18. A multi-function output device, including a scanner, and an associated data file provided on a storage medium that defines pre-determined data, usable to transform images scanned by the device into device-independent images that represent how the scanned sample would be perceived by a human observer, the data defining a single transform representing a Differential Transfer Function (DTF) that reflects a difference between a Modulation Transfer Function (MTF) that takes into account the scanner resolving power of the scanner and a Visual Transfer Function (VTF) that takes into account the sensitivity of a Human Visual System (HVS).

19. The multi-function output device of claim 18, where the data is in the form of space-domain convolution kernels.