Method and apparatus for thinning printed images

• US 5,250,934 A
• Filed: 12/31/1990
• Issued: 10/05/1993
• Est. Priority Date: 12/31/1990
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Jankowski, Henry P., Denber, Michel J.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): Luu, Matthew
• Application Number:
  US07/636,395
• Time in Patent Office: 1,009 Days
• Field of Search: 382/54, 382/55, 340/728, 340/730, 340/735, 340/793, 358/453, 358/486, 358/458 X, 358/463, 358/447, 358/445
• US Class Current: 345/611
• CPC Class Codes: G09G 5/20 Function-generator circuits, e.g. circle generators line or curve smoothing circuits
• CPC Class Codes: G09G 5/395 Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen G09G5/399 takes precedence
• CPC Class Codes: H04N 1/40093 Modification of content of picture, e.g. retouching geometric modifications H04N1/387
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

A method and apparatus are shown for improving bit-image quality in video display terminals and xerographic processors. In one embodiment, each scan line of a source image is ANDed with the scan line above to remove half-bits and thin halftones. In other embodiments, entire blocks of data are processed by bit-block transfer operations, such as ANDing a copy of the source image with a copy of itself shifted by one bit. Also, a source image can be compared to a shifted copy of itself to locate diagonal lines in order to place gray pixels bordering these lines.

Claims

1. A method for correcting half-bit errors due to write-white fonts in write-black xerographic and video output devices, comprising:

generating a source image comprising bit-image data in an image generation unit, said source image having half-bit errors due to a write-white font;

transmitting said source image to a processor as a series of binary data for each successive scan line of the source image;

storing in a first shift register in said processor all "on" binary digits, said shift register comprising a series of successive memory locations equal in number to one raster width, an input, and an output, whereby each datum appearing at said input is shifted through each of said successive memory locations to said output;

receiving from said image generation unit said binary data;

shifting each binary datum into said first shift register and performing a logical AND comparison between the same binary datum about to be shifted into said first shift register and the binary datum being shifted out of said first shift register, said logical AND comparison removing said half-bit errors and forming an output binary datum;

transmitting said output binary datum to a raster output scanner and converting said output binary datum to an output signal for an output device; and

displaying said output signal at said output device.

2. The method of claim 1, wherein data received from said image generation unit is shifted into a second shift register and the binary datum being shifted out of said second shift register is shifted into said first shift register and performing a logical AND comparison between the binary datum being shifted out said first shift register and said second shift register.

3. A method for improving bit-image quality in xerographic and video display devices, comprising:

generating a source image comprising bit-image data in an image generation unit;

transmitting said source image to a processor as a series of binary data for each successive scan line of the source image;

storing at least a part of said source image in said processor in a first memory buffer;

copying the image data stored in said first memory buffer into a second memory buffer;

shifting the image data in said second memory buffer;

performing a logical AND comparison between the image data in said first memory buffer and said second memory buffer and forming an output image;

transmitting said output image to a raster output scanner and converting said output image to a series of output signals for an output device; and

displaying said output signals at said output device.

4. The method of claim 3, wherein in said shifting step, the image data is shifted one bit upward.

5. The method of claim 3, wherein in said shifting step, the image data is shifted one bit to the right.

6. The method of claim 3, wherein in said shifting step, the bit image in the second memory buffer is shifted one bit upward, further comprising:

inverting the bit image in said second memory buffer after said shifting step;

performing a logical AND comparison between the image data in said first memory buffer and said second memory buffer and forming a first resulting image, and storing said first resulting image in said second memory buffer;

shifting the image in the second memory buffer one bit to the right;

performing a logical AND comparison between the image data in said first memory buffer and said second memory buffer and forming a second resulting image, and storing said second resulting image in said second memory buffer;

shifting the image in the second memory buffer one bit to the left; and

performing a logical AND comparison between the image data in said first memory buffer and said second memory buffer and forming a third resulting image, and storing said third resulting image in said second memory buffer; and

performing a logical OR comparison between the image data in said first memory buffer and said second memory buffer and forming said output image.

7. A method for improving bit-image quality in xerographic and video display devices, comprising:

generating a source image comprising bit-image data in an image generation unit;

transmitting said source image to a processor as a series of binary data for each successive scan line of the source image;

storing at least a part of said source image in said processor in a first memory buffer, said first memory buffer storing at least an on, an off, and an intermediate value;

copying the image data stored in said first memory buffer into a second memory buffer, said second memory buffer storing at least on and off values;

shifting the image data stored in said second memory buffer one bit to the right and one bit upward;

performing a logical AND comparison between the data stored in the first memory buffer and the data stored in the second memory buffer and forming a first resulting image, and storing said first resulting image in said second memory buffer;

shifting the image data stored in the second memory buffer one bit to the left;

performing a logical OR comparison between the image data in said first memory buffer and said second memory buffer and forming a second resulting image, and storing said second resulting image in said first memory buffer, whereby if a bit is on in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory buffer remains on, and if a bit is off in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory is changed to an intermediate value;

shifting the image data stored in the second memory buffer one bit to the right and one bit downward;

performing a logical OR comparison between the image data in said first memory buffer and said second memory buffer and forming a third resulting image, and storing said third resulting image in said second memory buffer, whereby if a bit is on in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory buffer remains on, and if a bit is off in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory is changed to an intermediate value;

transmitting said image of said first memory buffer to a raster output scanner and converting said image to a series of output signals for an output device; and

displaying said output signals at said output device.

8. The method of claim 8 further comprising:

copying the image data stored in said first memory buffer into a second memory buffer;

shifting the image data stored in said second memory buffer one bit to the left and one bit upward;

performing a logical AND comparison between the data stored in the first memory buffer and the data stored in the second memory buffer and forming a first resulting image, and storing said first resulting image in said first memory buffer;

shifting the image data stored in the second memory buffer one bit to the right;

performing a logical OR comparison between the image data in said first memory buffer and said second memory buffer and forming a second resulting image, and storing said second resulting image in said first memory buffer, whereby if a bit is on in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory buffer remains on, and if a bit is off in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory is changed to an intermediate value;

shifting the image data stored in the second memory buffer one bit to the left and one bit downward;

performing a logical OR comparison between the image data in said first memory buffer and said second memory buffer and forming a third resulting image, and storing said third resulting image in said second memory buffer, whereby if a bit is on in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory buffer remains on, and if a bit is off in said first memory buffer and its corresponding bit in said second memory buffer is on then said bit in said first memory is changed to an intermediate value.

9. A method for correcting half-bit errors due to write-white fonts in write-black xerographic and video output devices, comprising:

generating a source image comprising bit-image data in an image generation unit, said source image having half-bit errors due to a write-white font;

transmitting said source image to a processor as a series of binary data for each successive scan line of the source image;

storing in a first shift register in said processor all "on" binary digits, said shift register comprising a series of successive memory locations equal in number to one raster width, an input, and an output, whereby each datum appearing at said input is shifted through each of said successive memory locations to said output;

preloading in a second shift register data for the first scan line of the source image;

shifting subsequent data into a third shift register, such that each binary datum being shifted out of said third register is shifted into said second shift register and each binary datum shifted out of said second shift register is shifted into said first shift register;

receiving from said image generation unit said binary data;

shifting each binary datum into said third shift register;

logically comparing each binary datum in said second shift register to a corresponding bit in said first shift register and three corresponding adjacent bits in said third shift register to form an output binary datum, such that an on bit in said second shift register is turned off unless said corresponding bit in said first shift register and the three adjacent bits to said on bit in said third shift register are all off;

transmitting said output binary datum to a raster output scanner and converting said output binary datum to an output signal for an output device; and

displaying said output signal at said output device.