Image processing apparatus and computer readable medium for implementing image processing

• US 5,764,811 A
• Filed: 06/04/1996
• Issued: 06/09/1998
• Est. Priority Date: 06/24/1993
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kakutani, Toshiaki
• Primary Examiner(s): Kelley, Christopher S.
• Application Number:
  US08/657,286
• Time in Patent Office: 735 Days
• Field of Search: 382/252, 382/237, 382/239, 382/270, 382/272, 358/447, 358/445-458, 358/466
• US Class Current: 382/252
• CPC Class Codes: H04N 1/4053 with threshold modulated relative to input image data or vice versa

Abstract

An image processing apparatus 30, which can solve the problems of delay in dot generation in beginning portions of areas of low or high density and tailing after finishing areas of low or high density and carry out speedy binary coding image processing without accompanying side effects of quality depletion and without the need to utilize a complicated processing circuit: includes error correction means 34 which corrects multigradation image data 200 and outputs it, threshold error setting means which sets a binary coding threshold value based on the gradation value of said target pixel multigradation image data 200 and binary coding means 36 which, based on the set threshold value, converts the previously mentioned corrected pixel data into the previously mentioned bigradation image data and outputs it; the gradation value of the previously mentioned target pixel multigradation image data being data, the median value of the previously mentioned first gradation value and second gradation value being m and the previously mentioned threshold value being slsh, the previously mentioned threshold setting means, 36, when the gradation value of the previously mentioned target pixel multigradation image data is in the neighborhood of the previously mentioned first and second gradation values, the binary coding threshold value is set within the tolerance range shown in the following equations:

when data<m, data≦slsh≦(m+data)/2,

when data>m, (m+data)/2≦slsh≦data.

Claims

1. An image processing apparatus for converting multigradation image data into bigradation image data made from a first gradation value and a second gradation value, wherein said first gradation value<

said second gradation value, including;

an error correction means outputting corrected pixel data (corrected by adding an error diffused from adjacent already binary-coded pixels to a target pixel multigradation image data);

a threshold value setting means which sets a binary threshold value based on the gradation value of the multigradation image data of said target pixel; and

a binary coding means, outputting said bigradation image data changed from said corrected pixel data based on the set threshold value;

wherein with said target pixel multigradation image data gradation value (data), the median of said first gradation value and said second gradation value (m) and said threshold value (slsh), said threshold value setting means sets said binary coding threshold value slsh corresponding to said target pixel multigradation image data gradation value data, and satisfying at least one of the tolerance ranges shown in the following equations;

in the case where the value of data is close to said first gradation value, data≦

slsh≦

(m+data)/2,

in the case where the value of data is close to said second gradation value, (m+data)/2≦

slsh≦

data.

2. An image processing apparatus, wherein said threshold value setting means of claim 1, based on said target pixel multigradation image data gradation value data, sets said binary coding threshold value slsh according to the following equation:

space="preserve" listing-type="equation">slsh=(data*(K-1)+m)/K,

provided that K is a constant expressed by an integer greater than 2.

3. An image processing apparatus, wherein said threshold value setting means of claim 1, corresponding to said target pixel multigradation image data gradation value data, sets said binary coding threshold value slsh step by step.

4. An image processing apparatus, wherein said threshold value setting means of claim 1, based on said target pixel multigradation image data gradation value data, sets said binary coding threshold value slsh according to the following equations:

space="preserve" listing-type="equation">when data<

m-L1, slsh=data+L1,

space="preserve" listing-type="equation">when m-L1<

data<

m+L2, slsh=m,

space="preserve" listing-type="equation">when m+L2<

data, slsh=data-L2

provided that L1, L2 are constants expressed by integers between 0-m.

5. An article of manufacture comprising:

a computer readable medium having computer readable program code means embodied therein for converting multigradation image data into bigradation image data of a first and second gradation value, the computer readable program code means comprising;

an error correction means for correcting an input multigradation image data of a target pixel (data) by adding an error diffused from a proximal previously binary-coded pixel to said input to produce a corrected pixel data;

a threshold value setting means for setting a binary threshold value based on a gradation value of said input; and

a binary coding means which accepts said binary threshold value and said corrected pixel data and outputs said bigradation image data based on said threshold value and said corrected pixel data, wherein said first and second gradation values have a median m and said threshold value setting means sets said binary coding threshold value (slsh) satisfying at least one of the tolerance ranges shown in the following equations;

in the case where the value of input data is close to said first gradation value, data≦

slsh≦

((m+data)/2), and in the case where the value of input data is close to said second gradation value, ((m+data)/2)≦

slsh≦

data.

6. An article of manufacture comprising:

a computer readable medium having computer readable program code means embodied therein for converting multigradation image data into bigradation image data of a first and second gradation value according to claim 5, wherein said threshold value setting means sets said binary threshold value slsh according to the equation;

space="preserve" listing-type="equation">slsh=(data*(K-1)+m)/K,

wherein K is a constant expressed by an integer greater than 2.

7. An article of manufacture comprising:

a computer readable medium having computer readable program code means embodied therein for converting multigradation image data into bigradation image data of a first and second gradation value according to claim 5, wherein said threshold value setting means sets said binary threshold value step by step.

8. An article of manufacture comprising:

a computer readable medium having computer readable program code means embodied therein for converting multigradation image data into bigradation image data of a first and second gradation value according to claim 5, wherein said threshold value setting means sets said binary threshold value slsh according to the following equations;

space="preserve" listing-type="equation">when data<

m-L1, slsh=data+L1,

space="preserve" listing-type="equation">when m-L1<

data<

m+L2, slsh=m,

space="preserve" listing-type="equation">when m+L2<

data, slsh=data-L2,

wherein L1 and L2 are integer constants between 0 and m.

9. The article of manufacture according to claim 5, wherein said computer readable medium comprises a floppy disk.

10. The article of manufacture according to claim 6, wherein said computer readable medium comprises a floppy disk.

11. The article of manufacture according to claim 7, wherein said computer readable medium comprises a floppy disk.

12. The article of manufacture according to claim 8, wherein said computer readable medium comprises a floppy disk.

13. The article of manufacture according to claim 5, wherein said computer readable medium comprises information delivered by a computer network.

14. The article of manufacture according to claim 6, wherein said computer readable medium comprises information delivered by a computer network.

15. The article of manufacture according to claim 7, wherein said computer readable medium comprises information delivered by a computer network.

16. The article of manufacture according to claim 8, wherein said computer readable medium comprises information delivered by a computer network.

17. The article of manufacture according to claim 5, wherein said computer readable medium comprises a logic circuit.

18. The article of manufacture according to claim 6, wherein said computer readable medium comprises a logic circuit.

19. The article of manufacture according to claim 7 wherein said computer readable medium comprises a logic circuit.

20. The article of manufacture according to claim 8 wherein said computer readable medium comprises a logic circuit.