Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-07-27
2003-11-11
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S032000
Reexamination Certificate
active
06646716
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an apparatus and method for spatially modulating a light beam and imaging the modulated light onto a photosensitive media and in particular, to a method and apparatus for printing multiple simultaneous images onto a photosensitive media.
BACKGROUND OF THE INVENTION
Photographic images are traditionally printed onto photographic paper using conventional film based optical printers. The photographic industry is converting to digital imaging. One step in the digital imaging process uses images obtained from digital cameras or scanned film exposed in traditional photographic cameras to create digital image files that are then printed onto photographic paper.
The growth of the digital printing industry has led to multiple approaches to digital printing. One of the early methods used for digital printing was cathode ray tube (CRT) based printers such as the Centronics CRT recorder. This technology has several limitations related to the phosphor and the electron beam. The resolution of this technology is inadequate when printing a large format images, such as 8 inch by 10 inch photographic print. CRT printers also tend to be expensive, which is a severe shortcoming in a cost sensitive market. An additional limitation is that CRT printers do not provide sufficient red exposure to the media when operating at frame rates above 10,000 prints per hour.
Another commonly used approach to digital printing is the laser based engine as shown in U.S. Pat. No. 4,728,965. Such systems are generally polygon flying spot systems, which use red, green, and blue lasers. Unfortunately, as with CRT printers, the laser based systems tend to be expensive, since the cost of blue and green lasers remains quite high. Additionally, the currently available lasers are not compact. Another problem with laser based printing systems is that the photographic paper used for traditional photography is not suitable for a color laser printer due to reciprocity failure. High intensity reciprocity failure is a phenomenon by which photographic paper is less sensitive when exposed to high light intensity for a short period. For example, flying spot laser printers expose each of the pixels for a fraction of a microsecond, whereas optical printing systems expose the paper for the duration of the whole frame time, which can be on the order of seconds. Thus, a special paper is required for laser printers.
A more contemporary approach uses a single spatial light modulator such as a Texas Instruments digital micromirror device (DMD) as shown in U.S. Pat. No. 5,061,049. Spatial light modulators provide significant advantages in cost as well as allowing longer exposure times, and have been proposed for a variety of different printing systems from line printing systems such as the printer depicted in U.S. Pat. No. 5,521,748, to area printing systems such as the system described in U.S. Pat. No. 5,652,661. One approach to printing using the Texas Instruments DMD shown in U.S. Pat. No. 5,461,411 offers advantages such as longer exposure times using light emitting diodes (LED) as a source. See U.S. Pat. No. 5,504,514. However, this technology is very specific and not widely available. As a result, DMDs are expensive and not easily scaleable to higher resolution. Also, the currently available resolution is not sufficient for all printing needs.
Another low cost solution uses LCD modulators. Several photographic printers using commonly available LCD technology are described in U.S. Pat. Nos. 5,652,661; 5,701,185; and 5,745,156. Most ofthese involve the use of a transmissive LCD modulator, for example U.S. Pat. Nos. 5,652,661 and 5,701,185. While such a method offer several advantages in ease of optical design for printing, there are several drawbacks to the use of conventional transmissive LCD technology. Transmissive LCD modulators generally have reduced aperture ratios and the use of Transmissive Field-Effect-Transistors (TFT) on glass technology does not promote the pixel to pixel uniformity desired in many printing applications. Furthermore, in order to provide large numbers of pixels, many high resolution transmissive LCDs possess footprints of several inches. Such a large footprint can be unwieldy when combined with a print lens. As a result, most LCD printers using transmissive technology are constrained to either low resolution or small print sizes. Also, to print high resolution 8 inch by 10 inch images with at least 300 pixels per inch requires 2400 by 3000 pixels. Transmissive LCD modulators with such resolutions are not readily available. Furthermore, each pixel must have a gray scale depth to render a continuous tone print and do so uniformly over the frame size, which is not available in this technology.
An alternate approach is to utilize reflective LCD modulators which are widely used in the display market. Most of the activity in reflective LCD modulators has been related to projection display. The projectors are optimized to provide maximum luminous flux to the screen with secondary emphasis placed on contrast and resolution. To achieve the goals of projection display, most optical designs use high intensity lamp light sources. Additionally, many projector designs use three reflective LCD modulators, one for each of the primary colors, such as the design shown in U.S. Pat. No. 5,743,610. Using three reflective LCD modulators is both expensive and cumbersome. For projectors using a single reflective LCD modulator, color sequential operation is required. To maintain the high luminosity in combination with the color sequential requirements, a rotating color filter wheel is sometimes employed. This is yet another large, moving part, which further complicates the system.
The recent advent of high resolution reflective LCDs with high contrast, greater than 100:1, presents possibilities for printing that were previously unavailable. See U.S. Pat. Nos. 5,325,137 and 5,805,274. Specifically, a printer may be based on a reflective LCD modulator illuminated sequentially by red, green and blue, light emitting diodes. The reflective LCD modulator may be sub-apertured and dithered in two or three directions to increase resolution.
Dithering has been applied to transmissive LCD systems due to the already less than perfect fill factor. Incorporating dithering into a reflective LCD printing system would allow high resolution printing while maintaining a small footprint. Also, because of the naturally high fill factor present in many reflective LCD technologies, the dithering can be omitted with no detriment to the continuity of the printed image. The use of a reflective LCD serves to significantly reduce the cost of the printing system. Furthermore, the use of an area reflective LCD modulator sets the exposure times at sufficient length to avoid or significantly reduce reciprocity failure. The progress in the reflective LCD device field made in response to needs of the projection display industry have provided opportunities in printing applications. Thus, a reflective LCD modulator designed for projection display can be incorporated into the printing design with little modification to the LCD itself. Also, by designing an exposure system and data path with an existing projection display device allows incorporation of an inexpensive commodity item into a print engine.
Of the reflective LCD technologies, the most suitable to this design is one, which incorporates a small footprint with an integrated Complementary Metal Oxide Semiconductor (CMOS) backplane. The compact size along with the uniformity of drive offered by such a device will translate into better image quality than other LCD technologies. There has been progress in the projection display industry towards incorporating a single reflective LCD, primarily because of the lower cost and weight of single device systems. See U.S. Pat. No. 5,743,612. Of the LCD technologies, the reflective LCD with the silicon backplane can best achieve the high speeds required for color sequential operation. While this increased speed may n
Narayan Badhri
Ramanujan Sujatha
Talbot Dan S.
Wong Victor C.
Eastman Kodak Company
Fuller Rodney
Nelson Adrian Blish
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