System and method for enhancing graphic features produced by marking engines

• US 5,515,480 A
• Filed: 06/15/1994
• Issued: 05/07/1996
• Est. Priority Date: 06/15/1994
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: DP Tek, Inc.
• Inventors: Frazier, Allen
• Primary Examiner(s): Powell, Mark R.
• Assistant Examiner(s): Legree, Tracy M.
• Application Number:
  US08/260,085
• Time in Patent Office: 692 Days
• Field of Search: 395/109, 395/108, 395/112, 395/101, 395/117, 395/128, 395/129, 395/132, 358/537, 358/538, 358/536, 358/534, 358/298, 347/186, 347/188, 347/190, 347/195, 346/139 R
• US Class Current: 358/1.9
• CPC Class Codes: G06K 15/1209 Intensity control of the optical beam G06K15/1223 takes precedence
• CPC Class Codes: G06K 15/1223 Resolution control, enlarging or reducing, edge or detail enhancement
• CPC Class Codes: H04N 1/4058 with details for producing a halftone screen at an oblique angle H04N1/4056 takes precedence

Abstract

Gray scale input data, derived from continuous tone data, is transformed into pulse patterns for driving a marking engine so that a variety of marks of different sizes and shapes are formed in any given pixel region. Gray scale input data is arranged (received) as an array of pixels, in the native engine resolution, including multi-bit per pixel gray level values. A pixel in the array is analyzed in a transformation (window) to determine the pulse pattern output based on the gray level value of the current pixel and on the gray level values of adjacent vertical and horizontal pixels. The pulse pattern output for driving the marking engine in the current pixel location is adjusted by the transformation to produce sub-pixel sized marks of various shapes, sizes, positions, and orientations that, in combination with neighboring marks so produced, provides for the flexible production of marking patterns that contain a number of gray scale levels substantially exceeding the number of gray scale levels contained in the input data, and that enhance the simulation of graphic features produced. The transformation flexibly selects from an optimized subset of pulse patterns available to produce the most accurately calibrated tones and features based on the input data. Hence, gray scale input data is transformed into a pulse pattern output for driving a marking engine.

Claims

1. A system for producing graphic features on paper, said features encoded as an array of pixels, each having an associated value, comprising:

a marking engine for producing marks on said paper in a plurality of pixel locations in response to energizing pulses, each of said pixel locations being disposed on an associated scan line;

a memory storing a gray level value for each pixel in the array as a plurality of binary bits;

a feature detection circuit comprising electronic means for accessing a plurality of said pixel values in a feature detection window and for providing said plurality of pixel values as output;

a detection circuit comprising decoding logic receiving said plurality of pixel values in said feature detection window and responsively providing an address indication;

a look-up table providing one of a plurality of stored pulse code values as output in response to said address indication; and

a pulse generator receiving said pulse code output value and responsively providing an energizing pulse pattern to said marking engine;

said feature detection window accessing a first pixel value on a first scan line, a plurality of pixels adjacent said first pixel on said first scan line, and a plurality of pixels adjacent said first pixel on a plurality of scan lines adjacent said first scan line;

said energizing pulse pattern being provided within a pixel period and having a duration and position based on a feature pattern detected in said feature detection window;

said duration ranging from a fraction of said pixel period to said full pixel period;

said position corresponding to one of (1) the beginning of said pixel period;

(2) the end of said pixel period;

(3) the center of said pixel period;

(4) the beginning and end of said pixel period; and

said marks being responsively produced by said marking engine in patterns adapted for near-optimal simulation of graphic features including (1) highlights, (2) midtones, (3) shadows, and (4) edges, thereby enhancing the quality of a simulated image produced by said marking engine.

2. A system for enhancing graphic features produced by a marking engine, wherein graphic data is available from a multi-bit per pixel raster source having a resolution equivalent to a native resolution of said marking engine, comprising:

a pulse generator providing an energization pulse for a current pixel in a current pixel period to an energizing element of said marking engine in response to a pulse code indication;

a table containing a plurality of pulse code values optimized to enhance graphic features produced by said marking engine; and

a feature detection circuit decoding multi-bit value patterns for each of a plurality of pixels in said raster source and responsively indexing a pulse code value in said table to be provided to said pulse generator as said pulse code indication;

said feature detection circuit detecting one of a plurality of graphic features by detecting one of a plurality of value patterns in at least four pixels adjacent said current pixel and responsively indexing a corresponding graphic feature sub-table in said table containing a plurality of pulse code values optimized to enhance said detected graphic feature produced by said marking engine.

3. The system of claim 2 in which said feature detection circuit further decodes said current pixel value and responsively indexes a pulse code value from within said indexed sub-table.

4. The system of claim 2, in which said pulse code values are optimized by:

dividing said pixel period into a predetermined number of intervals n;

providing energization pulses to occur in at least one of a plurality of positions in said pixel period;

encoding a plurality of pulse codes for producing energization pulses in a pixel period, said pulses ranging in duration from one interval to n intervals incrementally in each of said plurality of positions;

providing each of said plurality of pulse codes to said pulse generator as said pulse code indication in predetermined sequence causing said marking engine to produce a plurality of graphic features in corresponding predetermined regions;

selecting a subset of said plurality of pulse codes corresponding to the best production of each of said plurality of graphic features; and

providing said subset of pulse codes in a corresponding graphic feature sub-table.

5. A system for enhancing graphic features produced by a marking engine, wherein graphic data is available from a multi-bit per pixel raster source having a resolution equivalent to a native resolution of said marking engine, comprising;

a pulse generator providing an energization pulse for a current pixel in a current pixel period to an energizing element of said marking engine in response to a pulse code indication;

a table containing a plurality of pulse code values optimized to enhance graphic features produced by said marking engine; and

a feature detection circuit decoding multi-bit value patterns for each of a plurality of pixels in said raster source and responsively indexing a pulse code value in said table to be provided to said pulse generator as said pulse code indication;

each pulse code value encoding a predetermined duration for said energization pulse and at least one predetermined position of said energization pulse disposed within said current pixel period.

6. A system for enhancing graphic features produced by a marking engine, wherein graphic data is available from a multi-bit per pixel raster source having a resolution equivalent to a native resolution of said marking engine, comprising:

a pulse generator providing an energization pulse for a current pixel in a current pixel period to an energizing element of said marking engine in response to a pulse code indication;

a table containing a plurality of pulse code values optimized to enhance graphic features produced by said marking engine; and

a feature detection circuit decoding multi-bit value patterns for each of a plurality of pixels in said raster source and responsively indexing a pulse code value in said table to be provided to said pulse generator as said pulse code indication;

said feature detection circuit detecting graphic features comprising highlight features and shadow features by detecting, respectively, one of a first and second threshold values in each of said plurality of pixels adjacent said current pixel and responsively indexing a respective sub-table in said table comprising one of (1) a plurality of pulse code values optimized to enhance highlight features produced by said marking engine, and (2) a plurality of pulse code values optimized to enhance shadow features produced by said marking engine.

7. A system for enhancing graphic features produced by a marking engine, wherein graphic data is available from a multi-bit per pixel raster source having a resolution equivalent to a native resolution of said marking engine, comprising:

a pulse generator providing an energization pulse for a current pixel in a current pixel period to an energizing element of said marking engine in response to a pulse code indication;

a table containing a plurality of pulse code values optimized to enhance graphic features produced by said marking engine; and

a feature detection circuit decoding multi-bit value patterns for each of a plurality of pixels in said raster source and responsively indexing a pulse code value in said table to be provided to said pulse generator as said pulse code indication;

said feature detection circuit detecting graphic features including right and left edges by comparing multi-bit values of said plurality of pixels adjacent said current pixel and responsively indexing a respective sub-table in said table comprising one of (1) a plurality of pulse code values optimized to enhance right edge features produced by said marking engine, and (2) a plurality of pulse code values optimized to enhance left edge features produced by said marking engine.

8. A system for enhancing graphic features produced by a marking engine, wherein graphic data is available from a multi-bit per pixel raster source having a resolution equivalent to a native resolution of said marking engine, comprising:

a pulse generator providing an energization pulse for a current pixel in a current pixel period to an energizing element of said marking engine in response to a pulse code indication;

a table containing a plurality of pulse code values optimized to enhance graphic features produced by said marking engine; and

a feature detection circuit decoding multi-bit value patterns for each of a plurality of pixels in said raster source and responsively indexing a pulse code value in said table to be provided to said pulse generator as said pulse code indication;

said table comprising a memory storing said plurality of pulse code values in a plurality of storage locations and providing one of said stored values as said pulse code indication in response to an address input; and

said feature detection circuit comprising combinatorial logic receiving multi-bit values for a plurality of pixels in said raster source and responsively providing said address input;

wherein one of a plurality of graphic features is detected from predetermined value patterns in said plurality of pixels and a corresponding pulse code value is indexed in said table causing said pulse generator to provide an optimized energization pulse in said corresponding pixel period, such that said marking engine produces an enhanced graphic feature.

9. A system for producing graphic features on paper, said features encoded as an array of pixels, each having an associated value, comprising:

a marking engine for producing marks on said paper in a plurality of pixel locations in response to driving pulses, each of said pixel locations being located on an associated scan line;

a memory buffer storing a value for each pixel in said array as a plurality of binary bits;

a transformation circuit receiving and determining the value of a first pixel and the value of at least one pixel adjacent said first pixel and responsively providing a pulse code output; and

a pulse generator receiving said pulse code output and responsively providing said driving pulses as output to said marking engine;

wherein said transformation circuit further receives and determines a plurality of values in a feature detection window corresponding to a plurality of pixels adjacent said first pixel on a same scan line and on adjacent scan lines, respectively, and responsively provides a pulse code output corresponding to the value pattern detected in said window;

wherein said driving pulses comprise pulse patterns which range in duration from a fraction of a pixel period to a full pixel period and are positioned within said pixel period responsively to said value pattern in said feature detection window;

wherein said pulse patterns are positioned at a location in said pixel period corresponding to one of (1) the beginning of said pixel period;

(2) the center of said pixel period;

(3) the end of said pixel period;

(4) both the beginning and end of said pixel period; and

said marks are responsively produced by said marking engine in patterns adapted to optimally simulate graphic features including (1) edges, (2) highlights, and (3) shadows, thereby enhancing the quality of a simulated gray image produced by said marking engine.

10. The system of claim 9, wherein said marking engine produces a charge region on said paper in each of said pixel locations in response to driving pulses during a corresponding pixel period;

said pulse generator provides pulse patterns in said pixel periods based on a value of said pulse code output;

said pulse patterns produce charge regions on said paper having predetermined charge densities; and

said marks are produced in a plurality of sizes and locations corresponding to regions of said paper where a predetermined charge density is exceeded.

11. The system of claim 9, wherein said transformation circuit further comprises a look-up table in a memory device.

12. The system of claim 11, wherein said transformation circuit further includes selection logic receiving and decoding said values and responsively providing an address output;

and

said memory device receives said address output and responsively provides said pulse code output.

13. A method of enhancing graphic features produced by a marking engine, said graphic features encoded as a plurality of pixels, each having an assigned value selected from a predetermined value range, said marking engine generating marks by energizing pixel locations disposed on scan lines in response to driving pulses in corresponding pixel periods, comprising the steps of:

(a) determining the value of a current pixel;

(b) detecting a predetermined value of at least one pixel adjacent said current pixel; and

(c) responsively generating a driving pulse in a corresponding pixel period, said pulse having a predetermined duration and position within said pixel period corresponding to the value determined in step (a) and at least one value detected at step (b);

wherein said marking engine responsively produces marks in a plurality of shapes and sizes enhancing the production of graphic features detected at steps (a) and (b).

14. The method of claim 13, in which step (b) comprises:

detecting at least one predetermined value for a plurality of pixels in a feature detection window;

said window comprising a plurality of pixels adjacent said current pixel on a same scan line and on adjacent scan lines, respectively.

15. The method of claim 14, in which step (c) further comprises the steps of:

(d) providing said predetermined pulse duration to be a fractional value of said pixel period duration; and

(e) generating a pulse of said predetermined duration at one of the following locations of said pixel period;

(1) at the beginning of said pixel period;

(2) at the end of said pixel period;

(3) at the center of said pixel period;

(4) at the beginning and end of said pixel period.

16. The method of claim 15, in which step (b) further comprises the steps of:

(a) comparing the values of a first pixel and a second pixel disposed adjacent said current pixel on said same scan line;

(b) detecting whether said values of said first and second pixel are equivalent to at least one threshold value;

(c) detecting whether the values of a third pixel and a fourth pixel are equivalent to at least one threshold value, said third and fourth pixels disposed adjacent said current pixel on adjacent scan lines, respectively; and

(d) responsively generating a pulse selection indication;

and in which step (c) further comprises;

(1) generating said driving pulse in response to said pulse selection indication.

17. The method of claim 16, in which steps (a), (b) and (c) detect one of a plurality of graphic feature contexts for said current pixel such as highlight, shadow and edge conditions.

18. The method of claim 17, in which step (c) further comprises the steps of:

(a) providing said predetermined pulse duration to be a fractional value of said pixel period duration; and

(b) generating a pulse of said predetermined duration at one of the following locations of said pixel period;

(1) at the beginning of said pixel period when a first edge condition is detected;

(2) at the end of said pixel period when a second edge condition is detected;

(3) at the center of said pixel period when a highlight condition is detected;

(4) at the beginning and end of said pixel period when a shadow condition is detected.

19. The method of claim 18, in which:

said pulse selection indication indexes a plurality of pulse code values contained in a table;

said pulse code values encoding position and duration information for said driving pulses;

said driving pulses being generated in response to said pulse code values; and

said table of pulse code values being optimized to enhance graphic features produced by said marking engine.