Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-10-19
2003-09-02
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S241000, C347S255000, C347S256000
Reexamination Certificate
active
06614462
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method for spatially and temporally modulating a light beam and more specifically to imaging a modulated light onto a light sensitive media.
BACKGROUND OF THE INVENTION
Photographic images are traditionally printed on photographic paper using conventional, film based optical printers. The photographic industry, however, is converting to digital imaging. One step in the digital printing process is to use 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 image, 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 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 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 Liquid Crystal Display (LCD) modulators. Several photographic printers using this commonly available technology are described in U.S. Pat. Nos. 5,652,661, 5,701,185, and 5,745,156. Most of these designs involve the use of a transmissive LCD modulator such as is depicted in U.S. Pat. Nos. 5,652,661 and 5,701,185. While such methods 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.
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 uniformly over the frame size, which is not available with this technology.
An alternate approach is to utilize reflective LCD modulators, which are widely accepted 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 the resolution.
Dithering has been applied to transmissive LCD systems due to the 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 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. While devices such as the Texas Instruments DMD can incorporate a secondary mask as shown in U.S. Pat. No. 5,754,217, the mask is displaced in some embodiments of the device, which makes manufacturing more difficult and adds to the processing complexity of the device.
Alternative forms of optical dithering are used to improve resolution in display systems incorporating LCD modulators. A calcite crystal or other electro-optic birefringent material can be used to optically shift the path of the image beam, where the amount of shift is dependent on the polarization characteristics of the image beam. This allows the shifting of one component of the image with respect to a second component of the image that has a different polarization. See U.S. Pat. No. 5,715,029 and 5,727,860. In addition to the use of birefringent material, U.S. Pat. No. 5,626,411 uses the law of refraction with isotropic optical media of different indices of refraction to displace one image component from a second image component. These methods of beam displacement are used in a dynamic imaging system and serve to increase resolution by interlacing raster lines to form two lines of sub-images. The two sub-images are imaged faster than in perceivable by the human visual system, so that the individual images are integrated into a composite image as seen by the observer.
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
Blish Nelson A.
Donner Janet
Ramanujan Sujatha
Blish Nelson Adrian
Eastman Kodak Company
Pham Hai
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