Image signal processing apparatus

• US 5,499,111 A
• Filed: 08/04/1992
• Issued: 03/12/1996
• Est. Priority Date: 08/06/1991
• Status: Expired due to Term

• Current Assignee: Panasonic Communications Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Graphic Communication Systems, Inc. (Panasonic Holdings Corporation)
• Inventors: Kobayashi, Kazuto, Sato, Shinichi, Ikeuchi, Takenobu
• Primary Examiner(s): Ip, Paul
• Application Number:
  US07/924,705
• Time in Patent Office: 1,316 Days
• Field of Search: 358/455, 358/80, 358/284, 358/283, 358/443, 358/456, 358/282, 358/75, 358/80, 358/456, 358/448, 358/462, 358/465, 358/466, 358/427, 358/456, 358/458, 358/459, 382/50-54, 382/22
• US Class Current: 382/252
• CPC Class Codes: H04N 1/4053 with threshold modulated relative to input image data or vice versa

Abstract

A correcting device corrects a multi-level image signal of a pixel of interest in accordance with corrective data. A binarizing device binarizes an output signal of the correcting device. A logic device receives an output signal of the binarizing device. A feedback device feeds an output signal of the logic device, which corresponds to at least two feedback pixels immediately preceding the pixel of interest in a scanning direction, back to an input side of the logic device. A calculating device derives a difference between an output signal of the logic device and the output signal of the correcting device, and generates the corrective data on the basis of the derived difference. An output signal of the logic device is a pseudo halftone image signal. The logic device operates as follows. A black-level signal is outputted as a signal of the pixel of interest when the output signal of the logic device which corresponds to the feedback pixel closest to the pixel of interest is black and the output signal of the logic device which corresponds to the other feedback pixel is white. A signal equal to the output signal of the binarizing device is outputted as a signal of the pixel of interest in other cases. A white-level signal is outputted as a signal of the pixel of interest when the output signal of the logic device which corresponds to the feedback pixel closest to the pixel of interest is white and the output signal of the logic device which corresponds to the other feedback pixel is black. A signal equal to the output signal of the binarizing device is outputted as a signal of the pixel of interest in other cases.

Claims

1. An image signal processing apparatus comprising:

correcting means for correcting a multi-level image signal of a pixel of interest in accordance with corrective data;

binarizing means for binarizing an output signal of the correcting means;

logic means receiving an output signal of the binarizing means;

feedback means for feeding an output signal of the logic means, which corresponds to at least two feedback pixels immediately preceding the pixel of interest in a scanning direction, back to an input side of the logic means;

calculating means for derived a difference between an output signal of the logic means and the output signal of the correcting means, and generating the corrective data on the basis of the derive difference; and

output means for outputting an output signal of the logic means as a pseudo halftone image signal;

wherein the logic means comprises;

means for outputting a black-level signal as a signal of the pixel of interest when the output signal of the logic means which corresponds to the feedback pixel closest to the pixel of interest is black and the output signal of the logic means which corresponds to the other feedback pixel is white, for outputting a signal equal to the output signal of the binarizing means as a signal of the pixel of interest in other cases; and

means for outputting a white-level signal as a signal of the pixel of interest when the output signal of the logic means which corresponds to the feedback pixel closest to the pixel of interest is white and the output signal of the logic means which corresponds to the other feedback pixel is black, and for outputting a signal equal to the output signal of the binarizing means as a signal of the pixel of interest in other cases.

2. An image signal processing apparatus comprising:

binarizing means for binarizing a multi-level input pixel signal;

converting means for converting an output signal of the binarizing means, which corresponds to a pixel of interest, into one of a signal of at least two successive black dots and a signal of at least two successive white dots;

calculating means for deriving a difference between an output signal of the converting means and the input pixel signal, and for generating corrective data on the basis of the derived difference; and

correcting means for correcting the input pixel signal, which corresponds to pixels near a pixel of interest, in accordance with the corrective data.

3. In an image signal processing apparatus outputting a plurality of black and white dots to represent a multi-level input pixel signal, the improvement comprising:

binarizing means for binarizing the multi-level input pixel signal; and

converting means for converting an output signal of the binarizing means, which corresponds to a pixel of interest, into one of a signal of at least two successive black dots and a signal of at least two successive white dots in a main scanning direction in accordance with states of pixels preceding the pixel of interest by two pixels or more.

4. In an image signal processing apparatus outputting a plurality of black and white dots to represent a multi-level input pixel signal, the improvement comprising:

binarizing means of binarizing the multi-level input pixel signal; and

converting means for converting an output signal of the binarizing means, which corresponds to a pixel of interest, into one of a signal of at least two successive black dots and a signal of at least two successive white dots in a sub scanning direction by referring to states of pixels preceding the pixel of interest by two pixels or more.

5. In an image signal processing apparatus outputting a plurality of black and white dots to represent a multi-level input pixel signal, the improvement comprising:

binarizing means of binarizing the multi-level input pixel signal; and

converting means for converting an output signal of the binarizing means, which corresponds to a pixel of interest into one of a signal of at lest two successive black dots and a signal of at least two successive white dots in one of a main scanning direction and a sub scanning direction by referring to states of pixels preceding the pixel of interest by two pixels or more.

6. An image signal processing apparatus comprising:

correcting means for correcting a multi-level input pixel signal in accordance with corrective data;

binarizing means for binarizing an output signal of the correcting means into a corresponding binary pixel signal;

reducing means for thinning out pixels in the binary pixel signal and thereby reducing the binary pixel signal; and

calculating means for deriving a difference between the binary pixel signal and the output signal of the correcting means, and for generating the corrective data on the basis of the derived difference;

wherein the calculating means comprises means for excluding the pixels, which are thinned out by the reducing means, from generating the corrective data to enable the correcting by the correcting means to be done only on pixels which are not thinned out by the reducing means.

7. An image signal processing apparatus comprising:

correcting means for correcting a multi-level input pixel signal in accordance with corrective data;

binarizing means for binarizing an output signal of the correcting means into a corresponding binary pixel signal;

reducing means for thinning out pixels in the binary pixel signal and thereby reducing the binary pixel signal; and

calculating means for deriving a difference between the binary pixel signal and the output signal of the correcting means to generate error data;

processing means for multiplying the error data of pixels near a pixel of interest by predetermined weight coefficients to generate weighted error data respectively, and for generating the corrective data on the basis of the weighted error data;

wherein the processing means comprises means for excluding the pixels, which are thinned out by the reducing means, from generating the corrective data to enable the correcting by the correcting means to be done only on pixels which are not thinned out by the reducing means.

8. An image signal processing apparatus comprising:

correcting means for correcting input image data in accordance with first corrective data;

binarizing means for binarizing an output signal of the correcting means;

subtracting means for calculating a difference between an output signal of the binarizing means and the output signal of the corrective means;

memory means for memorizing binary values of already-processed pixels, which are represented by the output signal of the binarizing means, near a currently-processed pixel;

first corrective-quantity determining means for determining second corrective data on the basis of the binary values of the already-processed pixels which are memorized by the memory means, the second corrective data depending on a difference between a theoretical dot size and an actual dot size in a recording system;

second corrective-quantity determining means for adding an output signal of the first corrective-quantity determining means and an output signal of the subtracting means to generate the first corrective data;

receiving means for receiving a signal representing whether or not the input image signal is effective; and

feeding means for feeding an output signal of the second corrective-quantity determining means to the correcting means as the first corrective data when the signal received by the receiving means represents that the input image signal is effective.

9. The image signal processing apparatus of claim 8, further comprising means for outputting data of zero to the correcting means as the first corrective data.

10. The image signal processing apparatus of claim 8, further comprising means for changing the second corrective data.

11. The image signal processing apparatus of claim 8, wherein the second corrective-quantity determining means comprises means for storing data of two sets of coefficients, means for generating a signal of a random number, means for selecting one of the two coefficient sets in accordance with the random number signal, and means for generating the first corrective data on the basis of the selected coefficient set, and wherein the random number signal generating means comprises first sub random number signal generators, a second sub random number signal generator different from the first sub random number signal generators, and means for selecting one of output signals of the first sub random number signal generator in response to an output signal of the second sub random number signal generator, and for outputting the selected output signal as the random number signal.

12. The image signal processing apparatus of claim 11, further comprising means for synchronizing an operation clock signal of the first sub random number signal generators with a clock signal of the input image signal.

13. The image signal processing apparatus of claim 11, further comprising means for synchronizing an operation clock signal of the second sub random number signal generator with a main scanning line component of the input image signal.

14. An image signal processing apparatus comprising:

an edge emphasizing filter for multiplying a pixel of interest and pixels adjoining the pixel of interest of an input multi-level image signal by first predetermined coefficients, and for calculating a filter correction value equal to a sum thereof;

correcting means for calculating and processing the filter correction value;

binarizing means for binarizing an output signal of the correcting means;

a subtraction circuit for calculating a subtraction value between an output signal of the binarizing means and the output signal of the correcting means; and

correction value calculating means for multiplying subtraction values of pixels adjoining a pixel to be binarized which are already outputted from the subtraction circuit by second predetermined coefficients, and for outputting resultants to the correcting means.

15. The image signal processing apparatus of claim 14, wherein the first coefficients have values which are different between positions vertically and horizontally adjoining the pixel of interest and positions obliquely adjoining the pixel of interest.

16. The image signal processing apparatus of claim 14, wherein the first coefficients have values of 1/8 as coefficients of positions vertically and horizontally adjoining the pixel of interest, and the first coefficients have negative values as coefficients of positions obliquely adjoining the pixel of interest, and wherein a sum of the first coefficient of the pixel of interest and the first coefficients of the adjoining pixels is equal to 1.

17. The image signal processing apparatus of claim 14, wherein a sum of the first coefficients is equal to 1 in a position of the pixel of interest, positions vertically and horizontally adjoining the pixel of interest, and positions obliquely adjoining the pixel of interest.

18. The image signal processing apparatus of claim 14, wherein a sum of the second coefficients is equal to 1.

19. The image signal processing apparatus of claim 14, wherein the binarizing means comprises a binarizing comparator for comparing input data and a predetermined threshold value to calculate a binary level.

20. The image signal processing apparatus of claim 14, wherein the binarizing means comprises a binarizing decoder for calculating a binary level from a sign bit and higher bits of data outputted from the correcting means.

21. An image signal processing apparatus comprising:

an edge emphasizing filter for multiplying a pixel of interest and pixels adjoining the pixel of interest of an input multi-level image signal by predetermined coefficients, and for calculating a filter correction value equal to a sum thereof;

a dither pattern generating circuit for outputting a signal in synchronism with the input image signal; and

a binarizing comparator for comparing a dither pattern outputted from the dither pattern generating circuit and the filter correction value to determine a binary level of the pixel of interest.

22. An image signal processing apparatus comprising:

an edge emphasizing filter for multiplying a pixel of interest and pixels adjoining the pixel of interest of an input multi-level image signal by predetermined coefficients, and for calculating a filter correction value equal to a sum thereof;

a dither pattern generating circuit for outputting a signal in synchronism with the input image signal;

an adder for adding a dither pattern outputted from the dither pattern generating circuit and the filter correction value; and

binarizing means for binarizing an output signal of the adder.

23. An image signal processing apparatus comprising:

an edge emphasizing filter for multiplying a pixel of interest and pixels adjoining the pixel of interest of an input multi-level image signal by predetermined coefficients, and for calculating a filter correction value equal to a sum thereof;

a dither pattern generating circuit for outputting a signal in synchronism with the input image signal;

an adder for adding a dither pattern outputted from the dither pattern generating circuit and the filter correction value being an output signal of the edge emphasizing filter; and

means for outputting information of whether a carry bit of the adder is present or absent as a binary value.

24. An image signal processing apparatus comprising:

an edge emphasizing filter including means for inputting a positive value "A" and a negative value "-B" as filter coefficients to emphasize edges in an image, means for using the input value "A" as filter coefficients of pixels adjoining a pixel of interest in main and sub scanning directions, means for using the input value "-B" as filter coefficients of pixels adjoining the pixel of interest in inclined directions, means for using a value "1+4B-4A" as a filter coefficient of the pixel of interest, means for multiplying the pixel of interest and the pixels adjoining the pixel of interest of an input multi-level image signal by the filter coefficients respectively, and means for outputting a sum thereof as a filter correction value;

correcting means for calculating and processing the filter correction value;

binarizing means for binarizing an output signal of the correcting means;

a subtraction circuit for calculating a subtraction value between an output signal of the binarizing means and the output signal of the correcting means; and

correction value calculating means for multiplying subtraction values of pixels adjoining a pixel to be binarized which are already outputted from the subtraction circuit by predetermined coefficients, and for outputting resultants to the correcting means.

25. The image signal processing apparatus of claim 24, wherein the binarizing means comprises a binarizing decoder for calculating a binary level from a sign bit and higher bits of data outputted from the correcting means.

26. An image signal processing apparatus comprising:

an edge emphasizing filter including means for inputting a positive value "A" and a negative value "-B" as filter coefficients to emphasize edges in an image, means for using the input value "A" as filter coefficients of pixels adjoining a pixel of interest in main and sub scanning directions, means for using the input value "-B" as filter coefficients of pixels adjoining the pixel of interest in inclined directions, means for using a value "1+4B-4A" as a filter coefficient of the pixel of interest, means for multiplying the pixel of interest and the pixels adjoining the pixel of interest of an input multi-level image signal by the filter coefficients respectively, and means for outputting a sum thereof as a filter correction value;

a dither pattern generating circuit for outputting a signal in synchronism with the input image signal; and

a binarizing comparator for comparing a dither pattern outputted from the dither pattern generating circuit and the filter correction value to determine a binary level of the pixel of interest.

27. An image signal processing apparatus comprising:

an edge emphasizing filter including means for inputting a positive value "A" and a negative value "-B" as filter coefficients to emphasize edges in an image, means for using the input value "A" as filter coefficients of pixels adjoining a pixel of interest in main and sub scanning directions, means for using the input value "-B" as filter coefficients of pixels adjoining the pixel of interest in inclined directions, means for using a value "1+4B-4A" as a filter coefficient of the pixel of interest, means for multiplying the pixel of interest and the pixels adjoining the pixel of interest of an input multi-level image signal by the filter coefficients respectively, and means for outputting a sum thereof as a filter correction value;

a dither pattern generating circuit for outputting a signal in synchronism with the input image signal;

an adder for adding a dither pattern outputted from the dither pattern generating circuit and the filter correction value; and

binarizing means for binarizing an output signal of the adder.

28. An image signal processing apparatus comprising:

correcting means for correcting input image data in accordance with a corrective value;

binarizing means for binarizing an output signal of the correcting means;

subtracting means for calculating a difference value between an output signal of the binarizing means and the output signal of the correcting means;

memory means for memorizing difference values outputted from the subtracting means as error values corresponding to a pixel of interest and pixels adjoining the pixel of interest; and

calculating means for reading out the error values corresponding to the pixels adjoining the pixel of interest from the memory means, for multiplying the readout error values by predetermined coefficients respectively, and for calculating a sum thereof and outputting an error correction value to the correcting means, the error correction value being equal to the sum.

29. An image signal processing apparatus comprising:

correcting means for correcting input image data in accordance with a corrective value;

binarizing means for binarizing an output sign of the correcting means;

subtracting means for calculating a difference value between an output signal of the binarizing means and the output signal of the correcting means;

error distributing means for making difference values outputted from the subtracting means into correspondence with a pixel of interest and pixels adjoining the pixel of interest, for multiplying the difference values by predetermined coefficients to generate errors respectively, and for outputting the errors for the respective pixels adjoining the pixel of interest; and

calculating means for sequentially correcting and adding an output signal of the error distributing means in correspondence with the respective pixels adjoining the pixel of interest to generate an error correction value, and for outputting the error correction value to the correcting means.