Method and apparatus for reproducing an image without salt and pepper specks

• US 5,682,250 A
• Filed: 12/20/1994
• Issued: 10/28/1997
• Est. Priority Date: 12/20/1994
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Jefferson, Darrell E.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US08/359,788
• Time in Patent Office: 1,043 Days
• Field of Search: 358/261.1-261.3, 358/429-433, 358/405, 371/22.3, 395/183.01, 395/183.06, 395/184.01, 395/185.01, 395/185.09
• US Class Current: 358/448
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

A computer implemented method of preventing the reproduction of specks while reproducing an image including specks represented via source scan lines. According to the method, on a scan like-by-scan line basis, each source scan line signal is transformed into speckless output run lengths. A source run length is selected and examined by a processor to determine whether it represents part of a speck. If the selected source run length might represent a speck, the processor determines whether the selected source run length can be protected from removal. If it cannot, the length of the selected run length and its subsequent neighbor are added to the output run length. As a result, the speck represented by the selected run length disappears from the image by merger with adjacent source run lengths. On the other hand, if the selected source run length is protected from removal, an output run length is output that represents source run length(s) previous to the selected source run length. A new output run length is then defined whose length and color are the same as the selected source run length. Afterward, another source run length is designated as the selected source run length.

Claims

1. A method of preventing reproduction of specks while reproducing an image including specks using a computer, the image being represented by source scan line signals, each source scan line signal representing a source scan line including a first multiplicity of source run lengths, each source run length representing a number of pixels, each pixel corresponding to a position on a reproduction device within an imaginary grid, each source run length having an associated color, the associated color being a one of white and black, alternating source run lengths within a source scan line having different associated colors, the computer including a processor coupled to a memory storing instructions to be executed by the processor to reproduce the image, the method comprising the computer-implemented steps of:

a) selecting a selected source run length from the first multiplicity of source run lengths of a first source scan line signal;

b) determining whether the selected source run length represents part of a speck;

c) if the selected source run length represents part of a speck;

1) determining if the selected source run length is coupled to a second source run length on a second source scan line, the associated color of the second source run length being the same as the associated color of the selected source run length, the second source run length not representing part of a speck;

2) preventing reproduction of the selected source run length if the selected source run length is not coupled to the second source run length; and

d) if reproduction of the selected source run length is not prevented, outputting a speckless output run length, the output run length extending to a start of the selected source run length.

2. The method of claim 1 wherein step b) comprises:

comparing the number of pixels associated with the selected source run length to a maximum speck size, the selected source run length representing a speck if the associated number of pixels is less than the maximum speck size.

3. The method of claim 1 wherein step c2) comprises:

storing a first value less than the maximum speck size in the memory at a memory location associated with the selected source run length.

4. The method of claim 1 further comprising the step of:

c3) insuring reproduction of the selected run length if the selected source run length is coupled to the second source run length.

5. The method of claim 4 wherein step c3) comprises:

storing a second value greater than the maximum speck size in the memory at a memory location associated with the selected source run length.

6. A device for removing salt and pepper specks from an image including salt and pepper specks, the device including:

a) a buffer having an input and an output, the input receiving a first multiplicity of source scan line signals representing a portion of the image, each source scan line signal representing a second multiplicity of source run lengths, each source run length representing a number of pixels, each source run length having an associated length and an associated color, the associated length indicating a number contiguous pixels of the associated color, the associated color being a one of white and black, alternating source run lengths within each source scan line having different associated colors, the buffer storing the first multiplicity of source scan line signals in a scan line store, the buffer also including a cumulative size store for indicating a cumulative size of source run lengths stored within the scan line store;

b) a processor coupled to the buffer for removing the salt and pepper specks from the image by generating speckless output run length signals from the first multiplicity of source scan line signals, the processor performing the transformation using a set of instructions;

c) a memory coupled to the processor for storing the set of instructions, the set of instructions causing the processor to;

1) select a selected source run length from a selected source scan line from the first multiplicity of source scan line signals;

2) determine whether the source selected run length represents a speck;

3) if the selected source run length represents a speck;

A) determine if the selected source run length is coupled to a second source run length on a second source scan line, the second scan line being a one of the first multiplicity of source scan lines, the associated color of the second source run length being the same as the associated color of the selected source run length, the second source run length not representing a speck;

B) prevent reproduction of the selected source run length if the selected source run length is not coupled to the second run length; and

4) defining a speckless output run length associated with the selected source run length if reproduction of the selected source run length is not prevented, the speckless run length having an output color that is a one of white and black.

7. A method of removing specks from an image including salt and pepper specks using a computer, the image being represented by source scan line signals, each source scan line signal representing a scan line including a multiplicity of source run lengths, each source run length having an associated length and an associated color, the associated length representing contiguous pixels of the associated color, the associated color being a one of white and black, alternating source run lengths within each source scan line having different associated colors, the computer including a processor coupled to a memory device storing instructions to be executed by the processor, the processor controlling a buffer for storing source scan line signals, the method comprising the computer-implemented steps of:

a) selecting a selected source run length from a selected source scan line signal stored in the buffer;

b) determining whether the selected source run length might represent a speck;

c) if the selected source run length might represent a speck;

1) determining if the selected source run length is coupled to a second source run length included in a second source scan line, the second scan line being represented by a second scan line signal stored in the buffer, the associated color of the second source run length being the same as the associated color of the selected source run length;

2) insuring reproduction of the selected source run length if a cumulative size of the selected source run length is greater than a maximum speck size;

d) if the selected source run length does not represent a speck;

1) determining if the selected source run length is coupled to the second source run length;

2) insuring reproduction of the second source run length if the second source run length is coupled to the selected source run length;

e) if the selected source run length does not represent a speck and;

1) outputting a speckless output run length associated with the selected source run length, the speckless output run length having an output color that is a one of white and black;

f) repeating steps a) through e) until every source run length included within the selected source scan line has been selected as the selected run length.

8. The method of claim 7 wherein the processor is coupled to a cumulative size store, the cumulative size store having a memory location associated with each source run length forming part of a one of the source scan line signals stored in the buffer, the memory location storing a value indicative of whether the associated source run length is to be removed.

9. The method of claim 8 wherein step c2) comprises:

storing a first value in the memory location associated with the selected source run length, the first value being greater than a maximum speck size.

10. The method of claim 9 wherein step d2) comprises:

storing a selected value in the memory location associated with the selected source run length, the selected value being greater than the maximum speck size.

11. The method of claim 7 wherein step b) further comprises the step of:

comparing the length associated with the selected source run length to the maximum speck size, the selected source run length not representing a speck if the length associated with the selected run length is greater than a maximum speck size.

12. The method of claim 8 wherein step b) further comprises the steps of:

A) comparing the length of the selected source run length to a maximum speck size, the selected source run length not representing a speck if the length associated with the selected source run length is greater than than the maximum speck size;

B) if the length of the selected source run length is less than the maximum speck size;

1) comparing a value stored in a memory location associated with the selected source run length to the maximum speck size, the selected source run length representing a speck if the value is less than the maximum speck size.

13. The method of claim 8 wherein step c2) further comprises the steps of:

A) generating a cumulative size by summing values stored in the cumulative size store associated with the selected source run length and the second source run length; and

B) storing the cumulative size in the memory location associated with the selected source run length.

14. The method of claim 13 further comprising the step of:

C) storing the cumulative size in the memory location associated with the second source run length.

15. The method of 8 wherein step c2) comprises:

A) storing a selected value in the memory location associated with selected source run length, the selected value being greater than a maximum speck size.