Patent
Distributed PWM halftoning unit and printer
| العنوان: | Distributed PWM halftoning unit and printer |
|---|---|
| Patent Number: | 6,191,868 |
| تاريخ النشر: | February 20, 2001 |
| Appl. No: | 09/146,348 |
| Application Filed: | September 03, 1998 |
| مستخلص: | In a halftoning unit of a laser printer and the like, a high speed, high density and high gradations halftoning is realized by multi-value implementation by clustered dot concentrated dither halftoning (known as a sub-matrix method) and PWM distributing gradation among the plurality of halftone dots with a small memory and circuit. For this purpose, the value of the difference between an input gradation value n.sub.i and a threshold value n.sub.c, .DELTA.n=n.sub.i -n.sub.c, is shortened within a range of 0 to .DELTA.h and the lower s bit of .DELTA.h is removed by a round-down or round-up process. Meanwhile, a threshold array is generated from an extended threshold pattern obtained by combining threshold patterns of 2.sup.s whose threshold interval is .DELTA.h, i.e. .DELTA.Ah.times.K, .DELTA.h.times.K+1, . . . , .DELTA..times.K+2.sup.(s-1). Thereby, a halftone dot dither process in which the PWM gradation increases distributively among the 2.sup.s dots may be realized with a small scale memory and circuit. |
| Inventors: | Shibuya, Takeshi (Ibaraki-ken, JPX); Okada, Tadashi (Hadano, JPX); Kanda, Masayuki (Hadano, JPX); Yoshino, Eiji (Hitachi, JPX); Onose, Atsushi (Hitachi, JPX); Inuzuka, Tatsuki (Hitachi, JPX); Nakamura, Toshiaki (Hitachinaka, JPX) |
| Assignees: | Hitachi, Ltd. (Tokyo, JPX) |
| Claim: | What is claimed is |
| Claim: | 1. A halftoning unit comprising a threshold array converting an input gradation value n.sub.i of an input pixel of 8 bits (=256 levels) per pixel into an output gradation value which can be rendered with less bit width by sequentially comparing with a threshold value n.sub.c of the threshold array; |
| Claim: | wherein the output gradation value is determined with the lower s bits of (n.sub.i -n.sub.c +n.sub.0) with respect to an adequate constant n.sub.0 and any one of values of s=1, 2, 3, and 4. |
| Claim: | 2. A printer comprising a threshold array for control of a multi-level output gradation value to an output minimum pixel by sequentially comparing an input gradation value n.sub.i of an inputted pixel of 8 bits (=256 levels) per pixel and a threshold value n.sub.c of the threshold array; |
| Claim: | 3. A printer according to claim 2, wherein an output image with respect to the increase of input gradation value is a halftone screen which consists of a lattice of halftone dots whose gradation increases cyclically among halftone dots of 2.sup.s. |
| Claim: | 4. A printer according to claim 2, wherein multi-color printing of at least two colors or more is performed per each color face and the threshold array and the value of s may be changed per each color face. |
| Current U.S. Class: | 358/19; 358/534; 358/456 |
| Current International Class: | H04N 152; H04N 1405 |
| Patent References Cited: | 4783837 November 1988 Kawamura et al. 5553200 September 1996 Accad |
| Other References: | P. Roetling, "Visual Performance and Image Coding", SPIE/OSA vol. 74 on Image Processing, 1976, pp. 195-199. |
| Primary Examiner: | Rogers, Scott |
| Attorney, Agent or Firm: | Antonelli, Terry, Stout & Kraus, LLP |
| رقم الانضمام: | edspgr.06191868 |
| قاعدة البيانات: | USPTO Patent Grants |
| الوصف غير متاح. |