METHOD AND APPARATUS FOR DATA CAPTURE FROM IMAGED DOCUMENTS

• US 20080316552A1
• Filed: 06/18/2008
• Published: 12/25/2008
• Est. Priority Date: 08/11/2000
• Status: Active Grant

• Current Assignee: McGraw Hill LLC
• Original Assignee: MHE Criterion LLC
• Inventors: Poor, David D.S.
• Granted Patent: US 7,911,660 B2
• Time in Patent Office: Days
• US Class Current: 358/509
• CPC Class Codes: G06K 17/0032 Apparatus for automatic testing and analysing marked record carriers, used for examinations of the multiple choice answer type teaching apparatus working with questions and answers G09B7/00
• CPC Class Codes: G06K 7/12 using a selected wavelength, e.g. to sense red marks and ignore blue marks
• CPC Class Codes: G06K 7/1447 extracting optical codes from image or text carrying said optical code
• CPC Class Codes: G06V 10/143 Sensing or illuminating at different wavelengths
• CPC Class Codes: G06V 10/22 by selection of a specific region containing or referencing a pattern; Locating or processing of specific regions to guide the detection or recognition
• CPC Class Codes: G06V 10/242 by image rotation, e.g. by 90 degrees
• CPC Class Codes: G06V 10/25 Determination of region of interest [ROI] or a volume of interest [VOI]

Abstract

Methods and apparatus are disclosed for locating an area of interest within a digital image of a form captured by an imaging scanner. Specific examples include methods and apparatus for optical mark reading with a digital imaging scanner. In many of the methods, an image of a response form is captured by a scanner, and “target” areas for possible responses are located within the image based upon an expected location being adjusted as necessary for certain error-inducing defects in the forms or scanning process. Also disclosed are steps to normalize the darkness values of pixels captured from an optically scanned form.

Claims

1-14. -14. (canceled)

15. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device, said method comprising the steps of:

a) scanning the form with an optical scanning device capable of producing pixel darkness values related to a relative amount of light reflected from the form;

b) recording the darkness value of individual pixels in the scan;

c) defining an area of the form to examine for determining pixel normalization parameters;

d) identifying the pixel darkness value corresponding to the least amount of light reflected within the area;

e) determining a normalization scale such that the pixel darkness value corresponding to the least amount of light reflected corresponds to a darkness value corresponding approximately to pure black; and

f) applying the normalization scale to the recorded darkness values to create normalized darkness values.

16. A method as in claim 15, wherein the optical scanning device is capable of producing pixel darkness values corresponding to a standard scale of darkness increments between pure black and pure white, and the step of determining a normalization scale is accomplished by the sub-steps of:

a) providing a plurality of look-up tables each having a differentiated scale of fewer increments than the standard scale, and

b) selecting a look-up table based upon the difference between the pixel darkness value corresponding to the least amount of reflected light and the standard scale value corresponding to pure black.

17. A method as in claim 15 wherein the standard scale has increments from 0-255 from pure white to pure black.

18. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device, said method comprising the steps of:

a) scanning the form with an optical scanning device capable of producing pixel darkness values related to a relative amount of light reflected from the form;

b) recording the darkness value of individual pixels in the scan;

c) defining an area of the form to examine for determining pixel normalization parameters;

d) identifying the pixel darkness value corresponding to the greatest amount of light reflected within the area;

e) determining a normalization scale such that the pixel darkness value corresponding to the greatest amount of light reflected corresponds to a darkness value corresponding approximately to pure white; and

f) applying the normalization scale to the recorded darkness values to create normalized darkness values.

19. A method as in claim 18, wherein the optical scanning device is capable of producing pixel darkness values corresponding to a standard scale of darkness increments between pure black and pure white, and the step of determining a normalization scale is accomplished by the sub-steps of:

a) providing a plurality of look-up tables each having a differentiated scale of fewer increments than the standard scale, and

b) selecting a look-up table based upon the difference between the pixel darkness value corresponding to the greatest amount of reflected light and the standard scale value corresponding to pure white.

20. A method as in claim 18, wherein the standard scale has increments from 0-255 from pure white to pure black.

21. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device, said method comprising the steps of:

a) scanning the form with an optical scanning device capable of producing pixel darkness values related to a relative amount of light reflected from the form;

b) recording the darkness value of individual pixels in the scan;

c) defining an area of the form to examine for determining pixel normalization parameters;

d) identifying the pixel darkness value corresponding to the greatest amount of light reflected within the area;

e) determining a normalization scale such that the pixel darkness value corresponding to the greatest amount of light reflected corresponds to a darkness value corresponding approximately to pure white and the pixel darkness value corresponding to the least amount of light reflected corresponds to a darkness value corresponding approximately to pure black; and

f) applying the normalization scale to the recorded darkness values to create normalized darkness values.

22. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device having multiple optical elements, said method comprising the steps of:

a) scanning the form with an optical scanning device having multiple optical elements capable of producing pixel darkness values related to a relative amount of light reflected off the form to the element;

b) recording the pixel darkness values produced by each optical element;

c) defining a section of the form to examine for determining pixel normalization parameters;

d) identifying, for each optical element, the pixel darkness value corresponding to the least amount of light reflected within the section;

e) determining a normalization scale for each optical element such that the pixel darkness value corresponding to the least amount of light reflected corresponds to a darkness value corresponding approximately to pure black; and

f) applying the appropriate normalization scale to the recorded darkness values to create normalized darkness values.

23. A method as in claim 22, wherein each optical scanning element is capable of producing pixel darkness values corresponding to a standard scale of darkness increments between pure black and pure white, and the step of determining a normalization scale is accomplished by the sub-steps of:

a) providing a plurality of look-up tables each having a differentiated scale of fewer increments than the standard scale, and

b) selecting a look-up table based upon the difference between the pixel darkness value corresponding to the least amount of reflected light and the standard scale value corresponding to pure black.

24. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device having multiple optical elements, said method comprising the steps of:

a) scanning the form with an optical scanning device having multiple optical elements capable of producing pixel darkness values related to a relative amount of light reflected off the form to the element;

b) recording the pixel darkness values produced by each optical element;

c) defining a section of the form to examine for determining pixel normalization parameters;

d) identifying, for each optical element, the pixel darkness value corresponding to the greatest amount of light reflected within the section;

e) determining a normalization scale for each optical element such that the pixel darkness value corresponding to the greatest amount of light reflected corresponds to a darkness value corresponding approximately to pure white; and

f) applying the appropriate normalization scale to the recorded darkness values to create normalized darkness values.

25. A method as in claim 24, wherein each optical scanning element is capable of producing pixel darkness values corresponding to a standard scale of darkness increments between pure black and pure white, and the step of determining a normalization scale is accomplished by the sub-steps of:

a) providing a plurality of look-up tables each having a differentiated scale of fewer increments than the standard scale, and

b) selecting a look-up table based upon the difference between the pixel darkness value corresponding to the greatest amount of reflected light and the standard scale value corresponding to pure white.

26. A method of normalizing the darkness value of pixels captured from a form by an optical scanning device having multiple optical elements, said method comprising the steps of:

a) scanning the form with an optical scanning device having multiple optical elements capable of producing pixel darkness values related to a relative amount of light reflected off the form to the element;

b) recording the pixel darkness values produced by each optical element;

c) defining a section of the form to examine for determining pixel normalization parameters;

d) identifying, for each optical element, the pixel darkness value corresponding to the greatest amount of light reflected to any optical element within the section;

e) identifying the pixel darkness value corresponding to the least amount of light reflected to any optical element within the section;

f) determining a normalization scale for each optical element such that the pixel darkness value corresponding to the greatest amount of light reflected corresponds to a darkness value corresponding approximately to pure white and the pixel darkness value corresponding to the least amount of light corresponds to approximately pure black; and

g) applying the appropriate normalization scale to the recorded darkness values to create normalized darkness values.

27. A method of normalizing the darkness value of pixels captured by optically scanning a form, said method comprising the steps of:

a) scanning the form with an optical imaging scanner having an array of optical elements capable of producing an image of the form and, for each pixel of the image a gray scale value of light reflected off the form, the scale ranging from 0 for pure black to 255 for pure white;

b) recording the gray scale value for each pixel;

c) defining an area within the image of the form to examine for determining pixel normalization parameters;

d) detecting, for each optical element, the highest recorded gray scale value within the area;

e) determining a normalization scale for each optical element based upon the difference between its highest gray scale value and 255; and

f) applying the associated normalization scale to pixels within the captured image to covert gray scale values to normalized values.

28. A method of normalizing the darkness value of pixels captured by optically scanning a form, said method comprising the steps of:

a) scanning the form with an optical imaging scanner having an array of optical element capable of producing an image of the form and, for each pixel of the image, a gray scale value ranging from 0 for pure black to 255 for pure white;

b) recording the gray scale value for each pixel;

c) defining an area within the image of the form to examine for determining pixel normalization parameters;

d) detecting, for each optical element, the highest recorded gray scale value within the area;

e) determining a white normalization scale for each optical element related to the difference between the highest gray scale value and 255;

f) applying the associated white normalization scale to pixels within the captured image;

g) detecting the lowest gray scale value recorded within the area;

h) determining a black normalization scale for each optical element related to the difference between the lowest gray scale value and 0; and

i) applying the black normalization scale to the white normalized values.

29. A method of normalizing the color intensity value of pixels captured from a form, said method comprising the steps of:

a) scanning the form with an optical imaging scanner capable of producing an image of the form and, for each pixel in the image, a color scale value related to a relative amount of light in a particular color band that is reflected from the form;

b) recording the color scale value for each pixel in the scan;

c) defining an area within the image of the form to examine for pixel normalization;

d) detecting the highest color scale value of pixels within the area;

e) determining a normalization parameter related to the difference between the highest color scale value of pixels within the area to the highest value of the scale; and

f) applying the normalization parameter to pixels within the captured image to covert a pixel'"'"'s color scale value to a normalized value.

30. A method of normalizing a color scale value of pixels captured from a form, said method comprising the steps of:

a) scanning the form with an optical imaging scanner capable of producing an image of the form and, for each pixel in the image, a color scale value related to a relative amount of light in a particular color band that is reflected by the form;

b) recording the color scale value for each pixel in the scan;

c) defining an area within the image of the form to examine for determining pixel normalization parameters;

d) detecting the highest and the lowest color scale values of pixels within the area;

e) determining a normalization parameter related to the difference between the highest color scale value of pixels within the area to the highest value of the scale, and related to the difference between the lowest color scale value of pixels within the area to the lowest value of the scale; and

f) applying the normalization parameter to pixels within the captured image to covert a pixel'"'"'s color scale value to a normalized value.

31. A method of converting a gray scale scanned image to a bi-tonal digital image, the method comprising the steps of:

a) scanning a form with an optical imaging scanner capable of producing an image of the form and, for each pixel in the image, a gray scale value related to a relative amount of light reflected by the form;

b) recording the gray scale value for each pixel in the scan;

c) defining an area within the image of the form to examine for pixel normalization;

d) detecting the highest gray scale value of pixels within the area;

e) determining a normalization parameter related to the difference between the highest gray scale value of pixels within the area to a value corresponding approximately to a pure white sheet;

f) applying the normalization parameter to pixels within the captured image of the form to covert a pixel'"'"'s gray scale value to a normalized value;

g) selecting a cut-off value within the gray scale; and

h) converting all pixels with normalized gray values above the cut-off value to the bi-tonal digit 0 (white), and all pixels with normalized gray values below the cut-off value to the bi-tonal digit 1 (black).

32. A method of optical mark reading (OMR) with an optical imaging scanner, said method comprising the steps of:

a) scanning a sheet printed with a plurality of OMR response targets with a scanner capable of producing an image of the sheet and any OMR response marks made thereon, and, for each pixel in the image, a scale value related to a relative amount of light reflected from the sheet;

b) recording the scale value of reflected light for each pixel;

c) defining an area within the image to examine for pixel normalization;

d) detecting the highest scale value of pixels within the area;

e) determining a normalization parameter related to the difference between the highest scale value of pixels within the area to a value corresponding approximately to a pure white sheet;

f) applying the normalization parameter to pixels within the captured image of the form to covert a pixel'"'"'s scale value to a normalized value;

g) selecting a cut-off value within the scale;

h) converting all pixels with normalized values above the cut-off to the bi-tonal digit 0 (white) and all pixels with normalized values below the cut-off to the bi-tonal digit 1 (black); and

i) interrogating pixels within a proscribed area around an expected location of an OMR response target for bi-tonal values of 1 as an indication of an OMR response mark