Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1988-11-08
1990-03-06
Britton, Howard W.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358 75, 358446, 358461, H04N 940, H04N 973
Patent
active
049070770
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention refers to the field of electronic reproduction technology and is directed to a method and to an apparatus for white balancing of the scanning elements of reproduction apparatus, particularly of black/white scanners and color scanners for the production of printing forms.
2. Description of the Prior Art
In a black/white scanner, a black-white original arranged on a rotating scanner drum is scanned point-by-point and line-by-line by a scanner light source and the scan light modulated by the tonal values of the scanned picture elements of the original in a scanner element is converted into an image signal by an opto-electrical transducer, for example by a photomultiplier, this image signal representing the tonal values between "black" and "white". The image signal is then modified according to a prescribed gradation curve whose corner points mark the tonal values "black" and "white" and whose course between the corner points is dependent on the printing parameters for the later printing and on the desired changes in tonal value of the reproduction in comparison to the original. The modified image signal controls the brightness of a recording element that exposes a film point-by-point and line-by-line. The exposed and developed film serves for the production of the printing form for the later printing of the original.
In a color scanner, the scan light acquired by the point-by-point and line-by-line scanning of a color original is split into three color components with dichroitic filters, these color components being converted into color signals by three-opto-electrical transducers. The color signals are likewise modified according to gradation curves and are then converted into the color separation signals in a color correction computer for recording the color separations, the printing forms for the later multi-color printing of the original being prepared from these color separations.
For standardizing the reproduction process, fixed reference signal values referred to as white level and black level are allocated to the corner points of the gradation curve. With reference to the white level, however, what is referred to as a white balancing must see to it that the maximum scan light proceeding from a white normal is always converted into an image signal value in the photomultiplier that corresponds to the normed white level, this being achieved by an appropriate adjustment of the sensitivity or, respectively, of the gain of the opto-electrical transducer.
The brightest image locations (white points) of the originals to be scanned are usually used as white normals in practice, whereby the scan light proceeding from the white point corresponds to the light of the scanner light source attenuated by the respective density value of the white point.
Since the scan light proceeding from the respective white point varies from original to original and dependent on the type of original carrier (film material given transparency originals and photographic paper given opaque originals) and since the sensitivity of the opto-electrical transducers that are employed cannot be kept constant over a longer time span, a white balancing is fundamentally carried out in practice before every original scanning. This white balancing is involved particularly in color scanners since at least three opto-electrical transducers must be balanced therein. In order to keep the time required for the white balancing short in comparison to the actual scan time for the originals, attempts have been made to optimally automate the white balancing.
For example, DE-A-No. 25 45 961 which corresponds to U.S. Pat. No. 4,136,360 discloses such an automatic white balancing. Therein, the scanner element is positioned to the respective white point of the original to be scanned and the scan light proceeding from the white point is converted into an image signal value in the photomultiplier as actual value for a control means. In the control means, the measured actual value is compared to
REFERENCES:
patent: 4136360 (1979-01-01), Hoffrichter et al.
patent: 4563707 (1986-01-01), Kishida
patent: 4626903 (1986-12-01), Giesche et al.
patent: 4639787 (1987-01-01), Isogai et al.
patent: 4647981 (1987-03-01), Froelich
patent: 4649423 (1987-03-01), Hoffrichter et al.
patent: 4843456 (1989-06-01), Iida et al.
Rohardt Juergen
Schulz-Hennig Joerg
Britton Howard W.
Dr. -Ing. Rudolf Hell GmbH
Vu Kim Yen
LandOfFree
Method and apparatus for white balancing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for white balancing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for white balancing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-52313