Photocopying – Projection printing and copying cameras – Identifying – composing – or selecting
Reexamination Certificate
2003-04-24
2004-05-18
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Identifying, composing, or selecting
C355S032000, C355S035000, C358S519000
Reexamination Certificate
active
06738127
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to printing apparatus for photosensitive media and more particularly relates to a printing apparatus and method for recording images onto a high contrast photosensitive medium.
BACKGROUND OF THE INVENTION
Over many years, apparatus and techniques for high-volume printing of images onto photosensitive media have been continuously refined and improved to reduce cost, boost efficiency, and maximize speed. In particular, printing of motion picture print films, distributed to theaters and other exhibitors, has benefited from this ongoing improvement process, so that today's methods for providing print films are considered by many film printing labs to be efficient and cost-effective.
It is illustrative to give a brief overview of the workflow for conventional motion picture print film manufacture, as shown in FIG.
1
. The image input to the printing process at a contact printer
120
is a master negative film
122
, carefully printed and prepared by a film lab as an intermediate for the printing process. Unimaged print film
124
is the material input to this process. At high rates of speed, a contact printing method is used at a printhead
126
to expose images from film master negative
122
onto unimaged print film
124
, to produce a positive print on an exposed print film
124
′. Exposed print film
124
′ is then developed, dried, and packaged for distribution to theaters and other exhibitors. In the print process itself, several hundred exposed print films
124
′ can be made from a single master negative film
122
.
With the advent of digital imaging capabilities, it is recognized that there are opportunities for improvement in methods and apparatus used for motion picture print film manufacture. In particular, two-dimensional spatial light modulator arrays, such as liquid crystal device (LCD) arrays and digital micromirror device (DMD) arrays, have been proposed for use in various printing applications. Just a few examples of printing apparatus and methods using these devices are disclosed in U.S. Pat. No. 6,215,547 (Ramanujan et al.) which discloses the use of a reflective LCD with a 3-color LED source; U.S. Pat. No. 6,480,259 (Wong et al.) which discloses a printing apparatus using polarization modulation with added polarization components for increasing contrast ratio; and U.S. Pat. No. 6,163,363 (Nelson et al.) which discloses the use of a DMD array for providing a printing apparatus with optimized contrast ratio.
In spite of the capabilities and advantages offered by digital imaging technologies, a number of significant hurdles remain. Among the more significant obstacles is writing speed. Two-dimensional spatial light modulators do not yet provide sufficient light levels or exhibit sufficient refresh rates for use in high-speed print film preparation, making it impractical to substitute these devices in printing applications where high-speed film exposure is currently used. This is particularly important since, as can be readily appreciated, high speed apparatus used for printing onto print film represent considerable capital investment. Until digital imaging technologies can offer significant advances in speed and lower cost, conventional contact printing techniques will likely be employed for the vast bulk of print film preparation.
However, while digital technologies may still not be optimal for print film exposure, spatial light modulators are being employed in print applications for preparing the negative master, where printing speeds are not critical and where digital imaging offers other advantages. For example, U.S. Pat. No. 6,215,547 (Ramanujan et al.) teaches the use of an LCD spatial light modulator for printing an image onto photosensitive media. Using approaches such as that disclosed in U.S. Pat. No. 6,215,547, it would be possible to use LCD spatial light modulators for writing images onto an intermediate negative film. Conventional contact-printing exposure techniques would then be used for printing from this intermediate master negative to the print film.
It is well recognized in the imaging arts that some amount of image degradation is inevitable with each intermediate stage. Thus, for example, even when printing from a negative of the highest quality, with a contact printer having ideal exposure levels and timing, some loss of image quality at the print film is inevitable. Typically, for example, there is some small amount of motion between the negative and the print in a contact printer, resulting in some loss of sharpness. Additionally, stray light in the printing process can contribute to some loss of contrast. Thus, it follows that, even with the relatively good performance of high-quality contact printers, there are advantages for image quality in eliminating an intermediate stage. Writing directly to print film, without the use of an intermediate master negative, would have inherent value for improved image quality. Even though it may take more time to write directly to print film, as compared with imaging by contact printing, there can be compelling reasons for providing print films having exceptionally high quality. For example, select motion picture theaters could charge a premium for showing a first run film having very high image quality, in comparison with most other theaters that project from print film prepared in the conventional manner.
Thus, it can be seen that there is a perceived need for being able to print directly to print film, using digital imaging techniques, even if this process is more time consuming than the conventional high-volume process. One alternative is to provide a printing apparatus expressly for this purpose, able to accept print film and to image directly onto the print film, without any intermediate negative stage. However, this first alternative would likely prove too costly for commercial use. Another alternative would be to begin with an existing printer designed for digital printing of master negative film media, and adapt such a printer to the additional task of imaging directly onto print film. A printer of this type could then be operated either to print a master negative or to print onto print film.
Adapting a printer for writing directly to print film presents a number of significant challenges, however. A first challenge is due to differences in media response. Referring to
FIG. 2
, there is shown a density versus log exposure curve for a typical intermediate negative film medium, such as would be conventionally used for master negative film
122
in FIG.
1
. Referring to
FIG. 3
, on the same scale as
FIG. 2
, there is shown a density versus log exposure curve for a typical print film, such as would be conventionally used as a contact print film
124
in FIG.
1
. Comparing
FIGS. 2 and 3
, it can be appreciated that there is significant difference in response between negative film and print film. The negative film can be characterized as a low contrast film. Print film, meanwhile, is characterized as a high contrast film. The slope of the D log E curve shows the relative gamma, or contrast characteristic, of the film medium. In terms of contrast, the negative film, as shown in
FIG. 2
, exhibits much lower contrast than the print film, as shown in FIG.
3
. For example, a typical intermediate negative film has a gamma of about 1.0. By comparison, a typical print film has a gamma of nearly 5.0 at the point of steepest slope.
The photosensitive media of
FIGS. 2 and 3
differ significantly in terms of dynamic range. Briefly, dynamic range for a photosensitive medium is based on the difference between the brightest and dimmest regions of exposure. The dynamic range of the light exposure required for the negative medium represented in
FIG. 2
is relatively high, on the order of 708:1. That is, the brightest exposure must be about 700 times greater than the dimmest exposure in order to produce a negative with a density range from zero to slightly over 2.0. For the print medium of
FIG. 3
, however, the dynamic range of
Roddy James E.
Zolla Robert J.
Adams Russell
Blish Nelson Adrian
Esplin D. Ben
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