Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-08-01
2003-04-22
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S255000
Reexamination Certificate
active
06552740
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a printing apparatus and method for monochromatic imaging onto a photosensitive media by spatially and temporally modulating a light beam and more particularly to a film recording apparatus capable of forming a high-resolution monochromatic image on photosensitive media.
BACKGROUND OF THE INVENTION
Conventional printers generally adapted to record images provided from digital data onto photosensitive media apply light exposure energy that may originate from a number of different sources and may be modulated in a number of different ways. In photoprocessing apparatus, for example, light exposure energy can be applied from a CRT-based printer. In a CRT-based printer, the digital data is used to modulate a Cathode Ray Tube (CRT), which provides exposure energy by scanning an electron beam of variable intensity along its phosphorescent screen. Alternately, light exposure energy can be applied from a laser-based printer, as is disclosed in U.S. Pat. No. 4,728,965 (Kessler et al.) In a laser-based printer, the digital data is used to modulate the duration of laser on-time or intensity as the beam is scanned by a rotating polygon onto the imaging plane.
CRT and laser-based printers perform satisfactorily for photoprocessing applications, that is, for printing of photographs for consumer and commercial markets. However, in an effort to reduce cost and complexity, alternative technologies have been considered for use in photoprocessing printers. Among suitable candidate technologies under development are two-dimensional spatial light modulators.
Two-dimensional spatial light modulators, such as those using a digital micromirror device (DMD) from Texas Instruments, Dallas, Tex., or using a liquid crystal device (LCD) can be used to modulate an incoming optical beam for imaging. A spatial light modulator can be considered essentially as a two-dimensional array of light-valve elements, each element corresponding to an image pixel. Each array element is separately addressable and digitally controlled to modulate light by transmitting or by blocking transmission of incident light from a light source by affecting the polarization state of light. Polarization considerations are, therefore, important in the overall design of support optics for a spatial light modulator.
There are two basic types of spatial light modulators in current use. The first type developed was the transmission spatial light modulator, which, as its name implies, operates by selective transmission of an optical beam through individual array elements. The second type, a later development, is a reflective spatial light modulator. As its name implies, the reflective spatial light modulator, operates by selective reflection of an optical beam through individual array elements. A suitable example of an LCD reflective spatial light modulator relevant to this application utilizes an integrated CMOS backplane, allowing a small footprint and improved uniformity characteristics.
Conventionally, LCD spatial light modulators have been developed and employed for digital projection systems for image display, such as is disclosed in U.S. Pat. No. 5,325,137 (Konno et al.) and in miniaturized image display apparatus suitable for mounting within a helmet or supported by eyeglasses, as is disclosed in U.S. Pat. No. 5,808,800 (Handschy et al.) LCD projector and display designs in use typically employ one or more spatial light modulators, such as using one for each of the primary colors, as is disclosed in U.S. Pat. No. 5,743,610 (Yajima et al.)
It is instructive to note that imaging requirements for projector and display use (as is typified in U.S. Pat. Nos. 5,325,137; 5,808,800; and 5,743,610) differ significantly from imaging requirements for printing by photoprocessing apparatus. Projectors are optimized to provide maximum luminous flux to a screen, which secondary emphasis placed on characteristics important in printing, such as contrast and resolution. Optical systems for projector and display applications are designed for the response of the human eye, which, when viewing a display, is relatively insensitive to image artifacts and aberrations and to image non-uniformity, since the displayed image is continually refreshed and is viewed from a distance. However, when viewing printed output from a high-resolution printing system, the human eye is not nearly as “forgiving” to artifacts and aberrations and to non-uniformity, since irregularities in optical response are more readily visible and objectionable on printed output. For this reason, there can be considerable complexity in optical systems for providing a uniform exposure energy for printing. Even more significant are differences in resolution requirements. Adapted for the human eye, projection and display systems are optimized for viewing at typical resolutions such as 72 dpi or less, for example. Photographic printing apparatus, on the other hand, must achieve much higher resolution, particularly apparatus designed for micrographics applications, which can be expected to provide 8,000 dpi for some systems. Thus, while LCD spatial light modulators can be used in a range of imaging applications for projection and display to high-resolution printing, the requirements on supporting optics can vary significantly.
Largely because spatial light modulators can offer significant advantages in cost and size, these devices have been proposed for different printing systems, from line printing systems such as the printer depicted in U.S. Pat. No. 5,521,748 (Sarraf), to area printing systems such as the system described in U.S. Pat. No. 5,652,661 (Gallipeau et al.) One approach, using a Texas Instruments DMD as shown in U.S. Pat. No. 5,461,411 offers advantages common to spatial light modulator printing such as longer exposure times using light emitting diodes as a source as shown in U.S. Pat. No. 5,504,514. However, DMD technology is very specific and not widely available. As a result, DMDs may be expensive and not easily scaleable to higher resolution requirements. The currently available resolution using DMDs is not sufficient for all printing needs. Furthermore, there is no clear technology path to increased resolution with DMDs.
A preferred approach for photoprocessing printers uses an LCD-based spatial light modulator. Liquid crystal modulators can be a low cost solution for applications requiring spatial light modulators. Photographic printers using commonly available LCD technology are disclosed in U.S. Pat. Nos. 5,652,661; 5,701,185 (Reiss et al.); and 5,745,156 (Federico et al.). Although the present invention primarily addresses use of LCD spatial light modulators, references to LCD in the subsequent description can be generalized, for the most part, to other types of spatial light modulators, such as the DMD noted above.
Primarily because of their early development for and association with screen projection of digital images, spatial light modulators have largely been adapted to continuous tone (contone) color imaging applications. Unlike other digital printing devices, such as the CRT and laser-based devices mentioned above that scan a beam in a two-dimensional pattern, spatial light modulators image one complete frame at a time. Using an LCD, the total exposure duration and overall exposure energy supplied for a frame can be varied as necessary in order to achieve the desired image density and to control media reciprocity characteristics. Advantageously, for photoprocessing applications, the capability for timing and intensity control of each individual pixel allows an LCD printer to provide grayscale imaging.
Most printer designs using LCD technology employ the LCD as a transmissive spatial light modulator, such as is disclosed in U.S. Pat. Nos. 5,652,661 and 5,701,185. However, the improved size and performance characteristics of reflective LCD arrays have made this technology a desirable alternative for conventional color photographic printing, as is disclosed in commonly-assigned copending U.S. Pat. application Ser.
Narayan Badhri
Ramanujan Sujatha
Talbot Dan S.
Wong Victor C.
Blish Nelson Adrian
Pham Hai
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