Efficient method for reading meter values by processing digital images of a meter

• US 20060045339A1
• Filed: 08/27/2004
• Published: 03/02/2006
• Est. Priority Date: 08/27/2004
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Baer, Richard L., Mahowald, Peter H., Butterworth, Mark M.
• Granted Patent: US 7,460,711 B2
• Time in Patent Office: Days
• US Class Current: 382/182
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06V 20/63 Scene text, e.g. street names
• CPC Class Codes: G06V 2201/02 Recognising information on displays, dials, clocks
• CPC Class Codes: G06V 30/10 Character recognition

Abstract

A method for reading a meter includes (1) capturing a first image of digits displayed by the meter, (2) roughly locating the digits by correlating the entire first image against symbols, (3) precisely locating the digits by correlating the digits against the symbols, which are now rotated, resized, and repositioned to maximize correlation, (4) determining and storing nominal centers of the digits in a nonvolatile memory. The method further includes (5) capturing a second image of the digits, (6) locating regions of interest in the second image according to the nominal centers, (7) determining vertical positions of full digits (or partial digits) in the regions of interest, (8) aligning symbols (or partial symbols) and the full digits (or the partial digits) according to the vertical position, and (9) correlating the symbol and the full digits (or the partial symbols and the partial digits).

Claims

1. A method for reading a meter, comprising:

capturing an image of digits displayed by the meter;

for any fully visible digit;

determining a vertical position of the digit;

retrieving a symbol from a symbol mask set;

aligning the symbol and the digit according to the vertical position of the digit; and

correlating the symbol and the digit.

2. The method of claim 1, further comprising repeating said retrieving, said aligning, and said correlating for other symbols in the symbol mask set, wherein the digit is determined to have a value of one of the symbols from the symbol mask set that produces a highest correlation value.

3. The method of claim 1, wherein:

the symbol mask set comprises a single mask image comprising the symbols in a sequential order; and

said retrieving a symbol from a symbol mask set comprises retrieving a portion of the mask image set at a predetermined offset.

4. The method of claim 1, wherein said determining a vertical offset of a center of the digit comprises:

for a region of interest having the digit in the digital image, performing a function to rows in the region of interest to produce a curve, wherein the function is selected from the group consisting of an “

or”

function and a “

sum”

function; and

determining a center of a protrusion in the curve as the vertical position of digit.

5. The method of claim 1, further comprising:

for any two digits in transition so that each digit is partially visible;

determining an antipodal vertical position of the two digits;

retrieving an intermediate portion between adjacent symbols from the symbol set;

aligning the intermediate portion and the two digits in transition according to the antipodal vertical position of the two digit; and

correlating the intermediate portion and the two digits.

6. The method of claim 5, further comprising repeating said retrieving, said aligning, and said correlating for other intermediate portions from the symbol mask set, wherein the two digits are determined to have values of two symbols in one intermediate portion from the symbol mask set that produces a highest correlation value.

7. The method of claim 5, wherein:

the symbol mask set comprises a single mask image comprising the symbols in a sequential order; and

said retrieving an intermediate portion between adjacent symbols from the symbol mask set comprises retrieving a portion of the mask image according to the antipodal vertical position.

8. The method of claim 1, further comprising, prior to said aligning and said correlating:

rotating the symbol; and

resizing the symbol.

9. A method for reading a meter, comprising:

capturing an image of digits displayed by the meter;

roughly locating the digits in the image by correlating the entire image against symbols from a symbol mask set;

after said roughly locating, precisely locating the digits by correlating the digits against the symbols that are rotated, resized, and repositioned to maximize correlation between the symbols and the digits;

determining nominal center positions of the digits; and

storing the nominal center positions of the digits in a nonvolatile memory.

10. The method of claim 9, wherein said correlating the entire digital image against symbols from a symbol mask set comprises:

multiplying corresponding pixels between a symbol and a portion of the digital image;

summing products of said multiplying as a correlation value at a location;

repeating said multiplying and summing for other portions of the digital image; and

repeating said multiplying, said summing, said repeating for other symbols from the symbol mask set.

11. The method of claim 9, wherein said determining nominal center positions of the digits comprises:

determining vertical positions and horizontal positions of the digits;

averaging the vertical positions of the digits to generate a nominal vertical position;

setting the horizontal positions of the digits as the nominal horizontal positions; and

storing the nominal vertical position and nominal horizontal positions in the nonvolatile memory.

12. The method of claim 11, wherein said determining vertical positions and horizontal positions of the digits comprising:

for an area in the image having a digit, performing a function to rows in the area to produce a first curve, and performing the function to columns in the region of interest to produce a second curve, wherein the function is selected from the group consisting of an “

or”

function and a “

sum”

function;

determining a first center of a first protrusion in the first curve as the vertical position of the digit; and

determining a second center of a second protrusion in the second curve as the horizontal position of the digit.

13. The method of claim 9, further comprising:

adjusting rotation and size of the symbols that maximize correlation between the symbols and the digits; and

storing the modified symbols in the nonvolatile memory.

14. The method of claim 9, further comprising:

capturing another image of the digits displayed by the meter;

locating a region of interest according to one of the nominal center positions of the digits;

for a fully visible digit in the region of interest;

determining a vertical position of the digit;

retrieving a symbol from the symbol mask set;

aligning the symbol and the digit according to the vertical position of the digit; and

correlating the symbol and the digit.

15. The method of claim 14, further comprising repeating said retrieving, said aligning, and said correlating for other symbols in the symbol mask set, wherein the digit is determined to have a value of one of the symbols from the symbol mask set that produces a highest correlation value.

16. The method of claim 14, wherein:

the symbol mask set comprises a single mask image comprising the symbols in a sequential order; and

said retrieving a symbol from a symbol mask set comprises retrieving a portion of the symbol mask set at a predetermined offset.

17. The method of claim 14, further comprising:

for two partially visible digits in the region of interest;

determining an antipodal vertical position of the two digits;

retrieving an intermediate portion between adjacent symbols from the symbol mask set;

aligning the intermediate portion and the two digits in transition according to the antipodal vertical position of the two digit; and

correlating the intermediate portion and the two digits.

18. The method of claim 17, further comprising repeating said retrieving, said aligning, and said correlating for other intermediate portions from the symbol mask set, wherein the two digits are determined to have values of two symbols in one of the intermediate portions from the symbol mask set that produces a highest correlation value.

19. The method of claim 17, wherein:

the symbol mask set comprises a single mask image comprising the symbols in a sequential order; and

said retrieving an intermediate portion between adjacent symbols from the symbol mask set comprises retrieving a portion of the mask image according to the antipodal vertical position.

20. The method of claim 14, further comprising, prior to said aligning and said correlating:

rotating the symbol; and

resizing the symbol.