Illuminator with light source arrays

Details Illuminator with light source arrays Illuminator with light source arrays

1997-11-26

2001-02-20

Lee, Cheukfan (Department: 2722)

Facsimile and static presentation processing

Natural color facsimile

Scanning

C358S505000, C358S512000

Reexamination Certificate

active

06191872

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the field of illuminators, and particularly to scanners incorporating such systems.
BACKGROUND OF THE INVENTION
Scanners convert hard copy analog images on a media into digital data. The media can be either transparent (for example, a photographic negative) or reflective (for example, paper). The use of scanners has become widespread for a variety of applications, including storing, manipulating, transmitting and displaying or printing copies of the images. For example, images captured in photographic media can be converted to digital data and stored on compact discs for readout and display as a video image or for printing with various types of color printers. In order to capture the photographic image digitally, an image frame is scanned with light, such as a line of light, and the light transmitted through the image is detected, typically as three primary color light intensity signals, and then digitized. The digitized values may be formatted to a standard for video display and stored on compact disc, magnetic media, or other suitable storage. Scanners take a variety of forms and the various common aspects of film digitizing, particularly line illumination and linear CCD-based digitizers, are described in greater detail in U.S. Pat. No. 5,012,346. For example, in one common type of scanner a one-dimensional sensor (typically referenced as a line sensor or one-dimensional array) is used and the illumination source directs a line of light onto the image bearing media, which is then moved one line at a time to scan the complete image line by line. In another scanner type, a two-dimensional sensor (typically referenced as an area array) is used, and the illumination source illuminates the entire image at the same time, so that the complete image is scanned in a single exposure. Scanners with area arrays are simpler to construct and are often preferred. However, scanners with line sensors provide higher resolution at lower equipment cost.
In order to obtain image signals which accurately represent a scanned image, the illumination source used in a scanner must meet certain requirements. One is that the light must be of sufficiently high intensity. While this can be obtained by used higher powered light sources, this leads to greater heat generation with required means to control such heat, and often to a light source with a shorter life. The illumination source should also provide uniform intensity of illumination so that the signal-to-noise ratio does not vary across the extent of the media being imaged. Although correction to the image signal can be used to remove the effects of such non-uniformity, doing so causes regions of low illumination to be more noisy than regions of high illumination from the higher gain applied there. Additionally, since the media to be illuminated may contain defects such as scratches, it is well known that the visibility of such defects may be reduced by distributing the light angularly at the media over angles of incidence of +45 degrees. This is generally accomplished either by using a diffusing element such as ground glass or a diffuse integrating chamber with or without an optical waveguide in close proximity to the media. Another desirable feature is that it be possible to vary the spectral distribution of light so as to accommodate different media types (e.g. a photographic reflection print, or a photographic negative having an orange colored “mask”). Many of these desirable features (such as intensity and uniformity of illumination, with adjustable spectral distribution) become more difficult to obtain in area array scanners.
It is possible to use as a light source, a broadband, white light source with appropriate filters to remove undesirable spectral components. One such known prior art arrangement is illustrated in FIG.
1
. In
FIG. 1
, an incandescent light bulb
2
is positioned in a reflector
4
to direct light to an interference filter
6
(sometimes referred to as dichroic filters). Interference filter
6
is constructed to reject infra-red (to which a scanner sensor may be sensitive). The filter may also be designed to improve color balance by removing unwanted components of visible light. Such color balancing interference filters are expensive to construct. Light from filter
6
then enters a non-imaging optic concentrator cone
8
and through an input port
11
of a integrating chamber
50
. The inside of integrating chamber
50
is made of a diffuse reflective material so that a relatively uniform beam of light enters an exit port
12
toward a media to be scanned, then onto an area array sensor.
The above illumination system is relatively effective. However, it is not possible to readily vary the spectral distribution of light leaving exit port
12
without an expensive color balance interference filter or other complex arrangements providing for different filters (for example, a filter wheel). Furthermore, a substantial proportion of light from bulb
2
will impinge upon interference filter
6
at different angles. Since the actual filtration of light by an interference filter is dependent upon the angle of incidence of the light to be filtered, with respect to the filter, this can result in different spectral outputs at different regions of interference filter
6
, and hence lack of uniformity of filtered light. However, in the case of
FIG. 1
this is not critical since interference filter
6
is only provided to broadly cut-off undesired infra-red. U.S. Pat. No. 5,191,406 discloses a line scanner in which lines of differently colored light emitting diodes (LEDs) are used to provide lines of illumination of different colors. The relative ON times of the different colored LEDs may be adjusted to provide a desired total spectral distribution for each line. However, the spectrum of a given LED (e.g. a green or red LED) is essentially fixed by LED characteristics. In U.S. Pat. No. 5,191,406 there is no means by which spectra in individual color regions (e.g. red, or green) can be controlled without having to replace the LEDs. Even with LED replacement a desired spectra in a single color channel (such as red, green, or blue) may not be obtainable with existing LEDs. Furthermore, no means is provided for also obtaining a uniform area of light provided for an area array scanner.
It would be desirable then, to provide illumination in an area array scanner, which is of relatively low power consumption, and can provide output spectra in each color channel which is not limited by characteristics of the actual light emitting device, while still maintaining good light uniformity throughout the two-dimensional illumination area.
SUMMARY OF THE INVENTION
The present invention then, provides in one aspect, a scanner comprising an illuminator comprising a plurality of arrays of semiconductor light emitting elements, each array having a different integrated spectral output, and a plurality of respective different interference filters each positional between a corresponding array and the media holder. A media holder to hold a media carrying an image for scanning, is positioned to receive filtered light from the illuminator. A sensor is positioned to receive light from the media holder so as to generate an image signal corresponding to an image on a media positioned at the media holder.
In another aspect, the present invention provides an illuminator comprising a plurality of illumination sources each having a different integrated spectral output. An integrating chamber is positioned to receive light from each of the illumination sources through respective input ports of the chamber, and direct the resulting integrated light through an output port of the chamber. Each of a plurality of interference filters is positioned between a corresponding input port and illumination source. The foregoing illuminator may also be used in a scanner with a media holder of the above type, positioned to receive light from the output port of the integrating chamber. When such concentrators are prese

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