WO1999045432A1

WO1999045432A1 - Photographic imaging process

Info

Publication number: WO1999045432A1
Application number: PCT/CA1999/000191
Authority: WO
Inventors: John O. Kobel
Original assignee: Imagetech Resource Laboratories Inc.
Priority date: 1998-03-05
Filing date: 1999-03-04
Publication date: 1999-09-10
Also published as: AU3243899A; CA2228690A1

Abstract

A photographic imaging process for producing large-format display media is disclosed. The process begins with a graphic digital file, which is sent to a computer having raster image processing (RIP). The RIP prepares data in four-color screen separation. The processed data is sent to an imagesetter, which sequentially or concurrently, exposes a photosensitive medium, preferably a clear-based silver halide film having a surface emulsion coated thereon containing three imaging media each capable of forming a color image upon imagewise exposure and processing. The clear based halide film records the screened color information for cyan, yellow, magenta and black. The silver halide film is then processed in RA-4 and compatible chemicals producing a clear-based color negative representing a composite of the four-color separations. The processed film is then exposed by a conventional optical enlarging system to a negative receiving material in order to produce a large-format display media such as a banner.

Description

PHOTOGRAPHIC IMAGING PROCESS

FIELD OF THE INVENTION

This invention relates to a photographic imaging process, and more particularly to a process for transferring digital text and imagery to photographic paper.

BACKGROUND OF THE INVENTION

The process of color printing by photolithography involves the separation of the colors of the image into a number of components (usually four) to be reproduced by printing inks of corresponding color, usually cyan, magenta, yellow and black (CMYK). Each color separation is converted into the form of a halftone dot pattern by which tone rendition is achieved in lithographic printing. The perceived density of a particular color on the final print depends on the relative size of the halftone dots in that area. The four halftone separation images are processed electronically and output separately onto black and white silver halide films commonly referred to as halftone separations or flats using a scanning laser device. Printing plates are prepared from halftone separations or their duplicates by contact exposure.

Independent of the photolithography process, the photographic industry utilizes numerous processes for the production of large-format display media from digital files. One method referred to as "direct-digital photo writers" employ independent blue, green and red lasers for exposing 2 the digitized information in continuous-tone onto conventional photographic color paper.

By nature, the method described above has several limiting characteristics. First, by writing the data to the photographic media at final format size requires an original digital file of sufficient size to provide the necessary information. To achieve the optimum results on output of large format prints, the file size required often becomes too cumbersome to logistically manage. It is not unusual for the technology to require files in excess 190 megabytes for each square meter of finished photographic display output.

In addition to the cumbersome file size, writing directly to final output size requires engineering a device physically large enough to image to the final print. The complexities of accurately transporting and imaging large areas of photographic media require expensive and sophisticated engineering and controls.

The three independent lasers incorporated in the device wear and fail at different intervals. Replacement of a failed laser requires an extensive alignment and re-focusing of the entire imaging system, resulting in costly service fees and lost production time. In conclusion, direct-digital photo writers require digital files that are difficult to manage, a large capital expenditure, are complex to operate and costly to maintain.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a digital imaging process for producing large-format color photographic display prints from digital files. In 3 accordance with the invention, this object is achieved with a digital imaging process comprising the steps of: providing a photosensitive element comprising a base having a surface emulsion coated thereon containing three imaging media each capable of forming a color image upon imagewise exposure and processing, obtaining color separation information representative of the cyan, magenta, yellow and black content of an electronically generated image; exposing said photosensitive element of step to emissions from a light source; and processing said photosensitive element, characterized in that said light source is a white-light laser, said whitelight laser being modulated by said color separation information with respect to each color and emitting radiation of variable intensity ranging from 450 to 680 nanometers (nm), at a wavelength in the region of the wavelength of maximum sensitivity of one of said imaging media capable of forming a color image such that a latent image representative of at least the cyan, magenta, and yellow of said color separation information is formed in each of said color forming media of said photosensitive element.

The process of the invention also includes the fact that the photosensitive element is a light-sensitive silver halide element and where the base is transparent. Accordingly, the process of the invention is characterized in that the step of processing the photosensitive element further includes the step of processing the exposed silver halide element to produce a complementary transparent film comprising three color images, a first color image being representative of the complementary color separation information for cyan, a second color image being representative of the complementary color separation information for magenta, and a third color image being representative of the complementary color separation information for yellow. Optionally, the photosensitive element may further 4 include a fourth image being representative of the color separation for black, being used as a contrast control layer, by modulating the white-light laser to emit all three colors simultaneously.

BRIEF DESCRIPTION OF THE DRA WINGS

The present invention and its advantages will be more easily understood after reading the following non-restrictive description of preferred embodiments thereof, made with reference to the following drawings in which:

Figure 1 is a schematic representation of the process according to a preferred embodiment of the invention;

Figure 2 is a schematic representation of the components used to carry out the process according to the invention; and Figure 3 is a schematic representation of the components within an imagesetter.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The invention is a digital imaging process for producing large-format color photographic display prints from relatively small digital files. The process is the result of joining several unrelated products and technologies from the photolithography and the photographic industries. When the technologies are used in combination, the resulting process produces unexpectedly sharp, large-format display prints.

The imaging process begins with a digital imaging file approximately 20 to 40 megabytes in size, which could be a scanned photograph or an 5

original image created by a digital camera, graphics software or any other means. The origin of the file is neither relevant nor important, although the invention concerns such files that are generally small compared to the digital files previously required in the art for producing large-format color photographic prints such as banners.

The digital file is transferred to an imaging computer for digital reprocessing into a color-separated format that is hardware addressable, i.e. in that it can drive an imagesetter. The conversion process is performed by a software raster image processor, commonly known as a RIP. The software raster image processor produces four separate colored images, i.e. cyan, magenta, yellow and black.

After completing the image processing, the software then sends the four colored separate images of the original to a standard imagesetter, such as the CELIX 2000^tm commercialized by FUJIFILM. It should be understood however that any commercially available imagesetter could be adapted to meet the objects of the invention. More particularly, the present invention is applicable for use with internal and external drum imagesetters.

Each separate image provides color and density information for cyan, magenta, yellow and black (cmyk) respectively. The imagesetter uses the RIP-processed color-separation information to begin the exposure process.

Within the imagesetter is a photosensitive element, which is preferably a light-sensitive silver halide element. The silver halide element comprises a transparent base having a surface emulsion coated thereon containing three imaging media each capable of forming a color image upon imagewise exposure and processing.

The exposure of each subtractive primary color layer is made by a single white-light laser, preferably an argon-krypton laser, but it could also be a laser-diode, modulated by an electronic color modulator to expose the imaging media with the primary color complimentary to the source. This is an 6

important difference from the prior art, as mentioned above, since the prior art uses three different lasers of three different colors. The invention provides for the use of a single, white-light laser, which is appropriately modulated. The laser is modulated with respect to each color and emits radiation of variable intensity ranging from 450 nm to 680 nm, at a wavelength in the region of the wavelength of maximum sensitivity of each of the imaging media capable of forming a color image such that a latent image representative of the cyan, magenta and yellow information of the color separation step is formed in each of the individual color forming media. The latent image can be formed either through sequential or simultaneous exposing of the imaging media.

It can be noted that the absorption maxima of the transparent emulsion YMC layers are approximately 480, 550, and 700 nm, respectively. Depending on the type of the source file, the laser can apply a halftone screen in resolution up to 800 dpi if the source file is pure images. If the source file is vector-type or graphics, which require greater resolution, the laser can apply a half-tone source in resolution up to 4000 dpi. It should also be understood that continuous tone images can also be produced. In other words, the clear-based, silver-halide negative film, or any other photosensitive material, in the imagesetter receives each exposure pass in sequential or concurrent order. The modulated laser-light exposes a specific layer of the photosensitive element that is sensitive to its complimentary color. The sequence of exposure is repeated in registration on a single sheet of photosensitive element for recording the cyan, magenta and yellow information if sequential exposure is used. A final composite exposure representing the black imaging information is exposed on the photosensitive element. The purpose of the final composite black exposure is for enhancing the contrast of the negative. The black is obtained by modulating the laser to output all three colors simultaneously. It is preferable 7 for the laser to be configured such that the simultaneous output of all three colors produces a "pure" grey.

When the exposure process is completed, the photosensitive element is removed from the imagesetter for processing in a conventional color print process using process RA-4 or compatible chemicals.

Once processed, the resulting clear-based color negative is exposed to a conventional silver halide color display material by means of a conventional optical enlarging system. The final output is a large-format photographic media. In accordance with yet another aspect of the invention, the element may be exposed to produce colors complementary to the original colors of the image, (in negative), or equivalent to the original colors of the image (in positive).

It should also be noted that the light sensitive element does not necessarily need to be clear, but could be opaque. In such a case, the process of the invention permits the production of a photographic print directly within the imagesetter up to 40x50 inches, i.e. for the production of a master image.

Accordingly, the invention combines several separate technologies from different industries to create large-format display materials of exceptional sharpness and clarity. The advantages of the invention are as follows: very small digital files are used to create high-quality, large format display prints by exposing a photosensitive element to each of the four colors obtained through color separation, processing the photosensitive element according to known techniques and enlarging the photosensitive element to print a large format display print using available enlarging equipment. Furthermore, the device uses a single, white-light laser in combination with a color modulator to create color in each exposure. The single laser design reduces equipment and maintenance costs. A 8 conventional graphic arts imagesetter is used for the purpose of creating the screened film. The process also makes use of a non-traditional intermediate film, which yields razor-sharp images from the digital files. The intermediate film is processed in RA-4 and compatible processing chemicals for faster access to the final product. The resulting negative is available to the user for production purposes in one-tenth the time that would be required to produce a conventional color negative. Additional prints of varying sizes from the same negative may be immediately printed in the optical enlarger without additional image processing. Finally, the process of the invention produces a final product which exhibits the qualities of a four-color printed piece.

Reference will now be made to the accompanying drawings in order to properly describe the same.

Figure 1 shows the steps for producing a large-format display media. The process begins with a graphic digital file, which is sent to a computer having raster image processing (RIP) software. The RIP software processes the data into four color screen separation. The four screens are sent to an imagesetter, which sequentially or concurrently, exposes a photosensitive medium, preferably a clear-based silver halide film having a surface emulsion coated thereon containing three imaging media each capable of forming a color image upon imagewise exposure and processing. The clear base halide film records the screened color information for cyan, yellow, magenta and black. The silver halide film is then processed in RA-4 and compatible chemicals producing a clear-based color negative representing a composite of the four-color separations. The processed film is then exposed by a conventional optical enlarging system to a negative receiving photographic material in order to produce a large-format display media such as a banner.

Figure 2 illustrates the various components used to carry out the invention. As mentioned above, a digital file is processed with a RIP to produce four separate images. The RIP processed data is sent to an internal 9 or external drum imagesetter. Either of the imagesetters includes a white- light laser and color modulator. The laser images a photo-sensitive, non- conventional (in the sense that the prior art does not use this step) clear base film, which can be sized from 4x5 inches (approximately 10x13 cm) to 11x17 inches (approximately 28x43 cm). The film is then processed using RA-4 or RA-4 compatible processes. The processed film is placed in a conventional photographic enlarger for murals or other large-format media. The resulting product is again processed with RA-4 or compatible processes, which results in a mural-sized photographic print. Figure 3 represents the interior of the imagesetter, in combination with the original data file and the RIP output. The imagesetter includes a white-light laser, which is color-modulated according to the RIP data. The output of the modulator is directed to a columnating lens, thereafter carried by an optical fiber to another columnating lens and optical fiber to the position of the original laser. The subsequent internal components of the imagesetter remain unchanged.

Although the present invention has been described in detail according to preferred embodiments thereof, it is understood that such detail is solely for illustrative purposes, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the following claims.

Claims

10CLAIMS

1. A digital imaging process, comprising the steps of: providing a photosensitive element comprising a base having a photosensitive surface emulsion coated thereon containing three imaging media each capable of forming a color image upon imagewise exposure and processing; obtaining color separation information representative of the cyan, magenta, yellow and black content of an electronically generated image; exposing said photosensitive element to emissions from a light source; and processing said photosensitive element, characterized in that said light source is a white-light laser, said white light laser being modulated by said color separation information with respect to each color and emitting radiation of variable intensity ranging from 450 to 680 nanometers (nm), at a wavelength in the region of the wavelength of maximum sensitivity of one of said imaging media capable of forming a color image such that a latent image representative of at least the cyan, magenta, and yellow of said color separation information is formed in each of said color forming media of said photosensitive element.

2. A process according to claim 1 , characterized in that said photosensitive element is a light-sensitive silver halide element and wherein said base is transparent; and wherein said step of processing said photosensitive element further includes the step of processing said exposed silver halide element to produce a complementary transparent film comprising three color images, a first color image being representative of the complementary color separation information for cyan, a second color image being representative of the 11 complementary color separation information for magenta, and a third color image being representative of the complementary color separation information for yellow.

3. A process according to claim 2, characterized in that said step of exposing said photosensitive element to said light source further includes forming a fourth image being representative of the color separation for black, being used as a contrast control layer, by modulating said white-light laser to emit all three colors simultaneously.

4. A process according to any one of claims 1 to 3, characterized in that said exposing of said photosensitive element is sequential.

5. A process according to any one of claims 1 to 3, characterized in that said exposing of said photosensitive element is concurrent.

6. A process according to any one of claims 1 to 5, characterized in that said process further includes the step of using said processed photosensitive element to expose a silver halide color photographic paper by means of an optical color enlarging system to color photographic paper to be processed in RA-4 and compatible chemicals.

7. A process according to claim 1 , characterized in that, said photosensitive element is a light-sensitive silver halide element and wherein said base is transparent, said process including the step of processing said exposed silver halide element to produce a positive transparent film comprising four color images; a first color image 12 being representative of the color separation information for cyan, a second color image being representative of the color separation information for magenta, a third color image being representative of the color separation information for yellow, and a fourth image being representative of the color separation information for black, being used as a contrast control layer.

8. A process according to claim 7, characterized in that said process further includes the step of using said positive transparent film to expose color photographic reversal paper, by replacing a conventional positive transparency in an optical color enlarger with said positive transparent film and projecting said positive transparent film onto a color reversal paper which is then processed through compatible process chemicals.

9. The use of a white-light laser modulated with a color modulator to expose a photosensitive element, said white light laser being modulated to emit radiation representative of cyan, magenta, yellow and black.