Image processing apparatus

• US 6,643,031 B1
• Filed: 12/21/1999
• Issued: 11/04/2003
• Est. Priority Date: 12/21/1998
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Takano, Gaku, Kanno, Hiroki
• Primary Examiner(s): Grant, II, Jerome
• Application Number:
  US09/467,976
• Time in Patent Office: 1,414 Days
• Field of Search: 358/1.9, 358/3.06, 358/3.09, 358/3.13, 358/3.16, 358/3.17
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/40037 the reproducing element being a laser
• CPC Class Codes: H04N 1/4056 the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]

Abstract

For an image signal having density equal to or larger than a predetermined threshold value, this invention realizes stable reproduction by reducing intermediate transition regions by increasing the intervals between pixels in the pixel arrangement of a non-image portion. For an image density signal whose density is smaller than the threshold value, the invention uses half-tone processing with higher resolution to thereby improve the image quality. This improves the reproducibility of pixel structures such as dots and line patterns at high densities, improves the stability of tone reproduction against environments, and improves the image quality.

Claims

1. An image forming method comprising the steps of:

reading an image signal in units of pixels;

generating a first driving signal corresponding to an image portion and a non-image portion in one pixel based on the read image signal of each pixel;

generating a second driving signal for clustering non-image portions of a plurality of pixels, on the basis of the read image signal of each pixel and an image signal of a peripheral pixel;

detecting whether the read image signal of each pixel has a density not less than a predetermined density;

selectively outputting the first driving signal if the image signal of the detected pixel has a density not less than the predetermined density;

selectively outputting the second driving signal if the image signal of the detected pixel has a density not more than the predetermined density;

outputting a laser beam on the basis of the selectively output first or second driving signal;

forming a latent image on a photosensitive body with the laser beam; and

forming an image by developing the formed latent image with toner.

2. A method according to claim 1, wherein the step of generating the second driving signal for clustering non-image portions of a plurality of pixels, on the basis of the read image signal of each pixel and the image signal of the peripheral pixel, comprises the steps of:

generating coordinate information in a main scan direction and coordinate information in a sub-scan direction on the basis of a pixel position of the read image signal;

generating a reference position signal in the pixel from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction;

quantizing the read image signal of each pixel in accordance with a predetermined threshold value and outputting the quantized signal as an image density signal;

outputting an image density signal of a pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction, the coordinate information in the sub-scan direction, and the quantized image density signal; and

generating a recording device driving signal from the reference position signal in the pixel and the image density signal of the pixel to be processed after pixel value shifting, and outputting the driving signal as a second driving signal.

3. A method according to claim 2, wherein the step of outputting the image density signal of the pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction, the coordinate information in the sub-scan direction, and the quantized image density signal, comprises the steps of:

buffering sequentially supplied quantized density signals of pixels to be processed and outputting each buffered value as peripheral pixel density data; and

outputting an image density signal after a shifting process, from the output peripheral pixel density data, the quantized image density signal, the coordinate information in the main scan direction, and the coordinate information in the sub-scan direction.

4. A method according to claim 3, wherein the step of outputting the image density signal after a shifting process, from the output peripheral pixel density data, the quantized image density signal, the coordinate information in the main scan direction, and the coordinate information in the sub-scan direction, comprises the steps of:

calculating a pixel shift value from the peripheral pixel density data, the quantized image density signal, the coordinate information in the main scan direction, and the coordinate information in the sub-scan direction;

storing the calculated pixel shift value; and

outputting the image density signal after a shifting process, from the stored pixel shift value, the peripheral pixel density data, the quantized image density signal, the coordinate information in the main scan direction, and the coordinate information in the sub-scan direction.

5. A method according to claim 4, wherein the step of outputting the image density signal after a shifting process, from the stored pixel shift value, the peripheral pixel density data, the quantized image density signal, the coordinate information in the main scan direction, and the coordinate information in the sub-scan direction, comprises the steps of:

outputting a shift amount operation mode signal on the basis of the coordinate information in the main scan direction and the coordinate information in the sub-scan direction;

outputting various image density signals and pixel shift values from the peripheral pixel density data, the image density signal, and the pixel shift value corresponding to the pixel to be processed;

decoding the shift amount operation mode signal and outputting a shift amount operation selector signal; and

selectively outputting the plurality of image density signals and pixel shift values on the basis of the output shift amount operation selector signal, thereby outputting an image density signal for clustering non-image portions of a plurality of pixels.

6. An image forming apparatus comprising:

reading means for reading an image signal in units of pixels;

first generating means for generating a first driving signal corresponding to an image portion and a non-image portion in one pixel based on the image signal of each pixel read by said reading means;

second generating means for generating a second driving signal for clustering non-image portions of a plurality of pixels on the basis of the image signal of each pixel read by said reading means and an image signal of a peripheral pixel;

detecting means for detecting whether the image signal of each pixel read by said reading means has a density not less than a predetermined density;

first output means for selectively outputting the first driving signal generated by said first generating means if the image signal of the pixel detected by said detecting means has a density not less than the predetermined density, and selectively outputting the second driving signal generated by said second generating means if the image signal of the pixel detected by said detecting means has a density not more than the predetermined density;

second output means for outputting a laser beam on the basis of the first or second driving signal selectively output by said first output means;

forming means for forming a latent image on a photosensitive body with the output laser beam from said second output means; and

developing means for forming an image by developing with toner the latent image formed by said forming means.

7. An apparatus according to claim 6, wherein said second generating means comprises:

third generating means for generating coordinate information in a main scan direction and coordinate information in a sub-scan direction on the basis of a pixel position of the image signal read by said reading means;

fourth generating means for generating a reference position signal in the pixel from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means;

third output means for quantizing the image signal of each pixel read by said reading means in accordance with a predetermined threshold value and outputting the quantized signal as an image density signal;

fourth output means for outputting an image density signal of a pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means, and the image density signal quantized by said third output means; and

fifth output means for generating a recording device driving signal from the reference position signal in the pixel generated by said fourth generating means and the image density signal of the pixel to be processed after pixel value shifting output from said fourth output means, and outputting the generated signal as a second driving signal.

8. An apparatus according to claim 7, wherein said fourth output means comprises:

sixth output means for buffering sequentially supplied quantized density signals of pixels to be processed and outputting each buffered value as peripheral pixel density data; and

seventh output means for outputting an image density signal after a shifting process, from the output peripheral pixel density data from said sixth output means, the image density signal quantized by said third output means, and the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means.

9. An apparatus according to claim 8, wherein said seventh output means comprises:

calculating means for calculating a pixel shift value from the output peripheral pixel density data from said sixth output means, the image density signal quantized by said third output means, and the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means;

storage means for storing the calculated pixel shift value; and

eighth output means for outputting the image density signal after a shifting process, from the pixel shift value stored in said storage means, the output peripheral pixel density data from said sixth output means, the image density signal quantized by said third output means, and the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means.

10. An apparatus according to claim 9, wherein said eighth output means comprises:

ninth output means for outputting a shift amount operation mode signal on the basis of the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said third generating means;

10th output means for outputting various image density signals and pixel shift values from the output peripheral pixel density data from said sixth output means, the image density signal quantized by said third output means, and the pixel shift value corresponding to the pixel to be processed stored in said storage means;

11th output means for decoding the output shift amount operation mode signal from said ninth output means and outputting a shift amount operation selector signal; and

12th output means for selectively outputting the plurality of image density signals and pixel shift values, output from said 10th output means, on the basis of the output shift amount operation selector signal from said 11th output means, thereby outputting an image density signal for clustering non-image portions of a plurality of pixels.

11. An image processing apparatus comprising:

detecting means for detecting whether a density of an image signal of an input pixel is not less than a predetermined density;

first converting means for converting the image signal into image signals of an image portion and a non-image portion for each pixel on the basis of the density of the image signal of each input pixel and a pixel position of each input pixel;

second converting means for converting the image signal into image signals of an image portion and a non-image portion for each pixel, on the basis of the density of the image signal of each input pixel and the pixel position of each input pixel, thereby clustering image signals of non-image portions of a plurality of pixels; and

output means for selectively outputting the image signal from said second converting means if said detecting means detects that the density of the image signal of the input pixel is not less than the predetermined density, and selectively outputting the image signal from said first converting means if said detecting means detects that the density of the image signal of the input pixel is not more than the predetermined density.

12. An apparatus according to claim 11, further comprising:

third converting means for converting the image signal into image signals of an image portion and a non-image portion for each pixel, on the basis of the density of the image signal of each input pixel and the pixel position of each input pixel, thereby clustering image signals of image portions of a plurality of pixels,

wherein said detecting means detects whether the density of the image signal of the input pixel is not less than a first density or not less than a second density higher than the first density, and

said output means selectively outputs the image signal from said second converting means if said detecting means detects that the density of the image signal of the input pixel is not less than the second density, selectively outputs the image signal from said first converting means if said detecting means detects that the density of the image signal of the input pixel is not more than the second density and not less than the first density, and selectively outputs the image signal from said third converting means if said detecting means detects that the density of the image signal of the input pixel is not more than the first density.

13. An apparatus according to claim 11, wherein said second converting means clusters image signals of non-image portions in units of two or three pixels.

14. An apparatus according to claim 11, wherein said second converting means comprises:

first generating means for generating coordinate information in a main scan direction and coordinate information in a sub-scan direction based on the pixel position of the input pixel;

second generating means for generating a reference position signal in the pixel from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said first generating means;

second output means for quantizing the image signal of the input pixel in accordance with a predetermined threshold value and outputting the quantized signal as an image density signal;

third output means for outputting an image density signal of a pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said first generating means and the image density signal quantized by said second output means; and

fourth output means for outputting as the reference position signal in the pixel generated by said second generating means and the image density signal of the pixel to be processed after pixel value shifting output from said third output means.

15. An apparatus according to claim 14, wherein said second output means quantizes the image signal of the input pixel by error diffusion in accordance with an image density of a peripheral pixel.

16. An image processing apparatus comprising:

detecting means for detecting whether a density of an image signal of an input pixel is not less than a predetermined density;

first storage means for storing first basic dither information of a dither matrix used to cluster non-image portions of a plurality of pixels;

second storage means for storing second basic dither information of a dither matrix used to cluster image portions of a plurality of pixels;

first output means for selecting the first basic dither information stored in said first storage means if the density of the image signal of the pixel detected by said detecting means is not less than the predetermined density, selecting the second basic dither information stored in said second storage means if the density of the image signal of the pixel detected by said detecting means is not more than the predetermined density, and outputting dither information, based on the first or second basic dither information selected and a pixel position of the input pixel, as a threshold value;

second output means for quantizing the image signal of the input pixel by the threshold value from said first output means and outputting the quantized image signal;

first generating means for generating coordinate information in a main scan direction and coordinate information in a sub-scan direction based on the pixel position of the input pixel;

second generating means for generating a reference position signal in the pixel from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said first generating means;

third output means for outputting an image density signal of a pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by said first generating means and the image density signal quantized by said second output means; and

fourth output means for outputting as the reference position signal in the pixel generated by said second generating means and the image density signal of the pixel to be processed after pixel value shifting output from said third output means.

17. An image processing apparatus comprising:

a plurality of converting means for converting each input pixel of a two-dimensional image in a main scan direction and a sub-scan direction into an image density signal;

a plurality of generating means provided in one-to-one correspondence with said plurality of converting means to generate a driving signal on the basis of the image density signal from a corresponding converting means; and

output means for selecting the driving signal from one of said generating means at each main scan period of each input pixel of the image, and periodically changing a main-scan-direction initial phase, selected whenever scan is performed, in the sub-scan direction and outputting the phase,

wherein said converting means include converting means for converting an input pixel corresponding to a high-density portion into an image density signal in a saturated range and converting means for converting an input pixel corresponding to a high-density portion into an image density signal in an unsaturated range.

18. An image processing apparatus comprising:

a plurality of converting means for converting each input pixel of a two-dimensional image in a main scan direction and a sub-scan direction into an image density signal;

a plurality of generating means provided in one-to-one correspondence with said plurality of converting means to generate a driving signal on the basis of the image density signal from a corresponding converting means; and

output means for selecting the driving signal from one of said generating means at each main scan period of each input pixel of the image, and periodically changing a main-scan-direction initial phase, selected whenever scan is performed, in the sub-scan direction and outputting the phase,

wherein said converting means include converting means for converting an input pixel corresponding to a high-density portion into an image density signal in a saturated range, converting means for converting an input pixel corresponding to a high-density portion into an image density signal in an unsaturated range, converting means for converting an input pixel corresponding to a low-density portion into zero or an image density signal in a range within which no image is formed, and converting means for converting an input pixel corresponding to a low-density portion into an image density signal in a range within which an image is formed.