US 4,907,077 A · Method and apparatus for white balancing

Abstract

Process and apparatus for the white balancing of the opto-electrical converters of the scanning elements in reproducers for the point-by-point and line-by-line scanning of black and white documents and color documents. The light from the illuminant of the documents being scanned is converted in the opto-electrical converters into video signal levels or color signal levels, and the sensitivity or amplification of the opto-electric converters is so set that the video signal levels or color signal levels correspond to preset reference signal levels. The inconvenient process of scanning the illuminant of the document to be scanned, in order to obtain the light required for white balance, is replaced by a process by which the light from the scanning light source may be dimmed by means of a regulable iris diaphragm, thus corresponding to the scanning light from the illuminant of the document to be scanned. Adjustment of the iris diaphragm may be interrupted in order to reduce the time of operation, and the resulting inexact light reduction may be compensated for by correcting the reference signal levels.

Claims38

Dependent claims

A method for white balancing of the opto-electrical transducer in a scanner element for point-by-point and line-by-line scanning of an original illuminated by a scanner light source and for converting the scan light modulated with the density values of the scanned picture elements into an image signal, wherein for white balancing before scanning of the originals, light is generated with a light power that corresponds to the light power of the scan light proceeding from the brightest location of the original, the white point, and converting the generated light into an image signal value (U.sub.B) in the transducer (13), wherein the image signal value (U.sub.B) of the white point is measured and compared to a reference signal value (U.sub.BSo11) that the image signal value of the white point should reach, and wherein the image signal value (U.sub.B) of the white point to the reference signal value (U.sub.BSo11) by varying the sensitivity or, respectively, the gain of the transducer (13), comprising the steps of:

(a) identifying the transmissivity of the white point of a transparency original or the reflectivity of the white point of an opaque original and retaining it as a light attenuation factor (K.sub.L);
(b) measuring the light power of the scanner light source (5) and calculating a rated light power value (UL.sub.So11) from the measured light power (U.sub.L) and from the light attenuation factor (K.sub.L), this rated light power value corresponding to the light power of the scan light proceeding from the white point of the original;
and
(c) attenuating the light of the scanner light source (5) by stopping down and setting the image signal value (U.sub.B) acquired by the attenuated light to the reference signal value (U.sub.BSo11).

1 more element

Apparatus for white balancing of the opto-electrical transducer of a scanner element for point-by-point and line-by-line scanning of black/white originals, comprising:

(a) a scanner light source (5) for the illumination of the black/white originals;
(b) the scanner element (3) contains a scanner objective (9), a scanner diaphragm (10) and a transducer circuit (13;
15;
16;
18;
49) comprising an opto-electrical transducer for the conversion of the scan light into an image signal (U.sub.B),
(c) a circuit arrangement (29) for setting the sensitivity or, respectively, the gain of the transducer circuit (13;
15;
16;
18;
49), a control input thereof being connected to the output of the circuit arrangement (29) and the output thereof being connected to the first input of the circuit arrangement (29), whereby the second input of the circuit arrangement (29) can be supplied with a reference signal value (U.sub.BSo11) for the image signal (U.sub.B),
(d) a light attenuator (22;
23;
37) controllable by a control signal, said light attenuator being arranged in the beam path of the scanner element (3) preceding the scanner diaphragm (I0) for attenuating the light of the scanner light source (5) by a prescribable light attenuation factor (K.sub.L);
and
(e) a light-control circuit (28;
30;
31) whose output is connected to the control input of the light attenuator (22;
23;
37) and whose first input can be supplied with a measured actual light power value (U.sub.List) and whose second input can be supplied with the prescribable light attenuation factor (K.sub.L) for generating the control signal for the light attenuator (22;
23;
37).

19 more elements

A method for white balancing of the opto-electrical transducer in a color scanner element for point-by-point and line-by-line scanning of a color original illuminated by a scanner light source, for splitting the scan light modulated with the density values of the color original into color components for each color channel and for converting the color components of the color channels into color signals, wherein for white balancing before scanning of the original, light is generated with a light power that corresponds to the light power of the scan light emanating from a brightest location of the color original, the white point, and light is converted into color signal values (U.sub.B), wherein the color signal values (U.sub.B) of the white point are measured and compared to reference signal values (U.sub.BSo11) allocated to the individual color channels, these reference signal values being assumed to reached the color signal values (U.sub.B) of the white point, and wherein the color signal values (U.sub.B) of the white point to the appertaining reference signal values (U.sub.BSo11) by varying the sensitivity or, respectively, the gain of the opto-electronic transducer (13), comprising the steps of:

(a) identifying the transmissivity of the white point of a transparency original or the reflectivity of the white point of an opaque original and retaining it as a light attenuation factor (K.sub.L);
(b) measuring the light power of the scanner light source (S) and calculating a rated light power value (U.sub.LSo11) from the measured light power (U.sub.L) and from the light attenuation factor (K.sub.L), this rated light power value corresponding to the light power of the scan light emanating from the white point of the color original;
and
(c) attenuating the light of the scanner light source (5) and generating the color signal values (U.sub.B) with the attenuated light and setting them to the appertaining reference signal values (U.sub.BSo11).

1 more element

Apparatus for white balancing an opto-electrical transducer of a color scanner element for point-by-point and line-by-line scanning of color originals, comprising:

(a) a scanner light source (5;
6) for illuminating the color originals,
(b) the color scanner element contains a scanner objective (9), a scanner diaphragm (10), means (75;
76;
77) for splitting the scan light into color channels as well as for every color channel, a color filter for separating the color components and a transducer circuit comprising an opto-electrical transducer (13) for conversion of the color component into a color signal, and
(c) a circuit arrangement (29) in every color channel for setting the sensitivity or, respectively, the gain of the appertaining transducer circuit (13;
15;
16;
18;
49), a control input thereof being connected to the output of the appertaining circuit arrangement (29) and the output thereof being connected to the first input of the circuit arrangement (29), whereby the second input of every circuit arrangement (29) is supplied with a reference signal value (U.sub.BSo11) for the color signal (U.sub.B) of the appertaining color channel,
(d) a light attenuator (22;
23;
37) controllable by a control signal, said light attenuator being arranged in the beam path of the color scanner element before the scanner diaphragm (10) for attenuating the light of the scanner light source (5) by a prescribable light attenuation factor (K.sub.L);
and
(e) a light-control circuit (28;
30;
31) whose output is connected to the control input of the light attenuator (22;
23;
37) and whose first input receives a measured actual light power value (U.sub.LIst) and whose second input receives the prescribable light-attenuation factor (K.sub.L), for generating the control signal for the light attenuation (22;
23;
37).

18 more elements

Dependencies are inferred from the claim text.

Method and apparatus for white balancing

Life of this patent

Method and apparatus for white balancing

Life of this patent

Abstract

Claims38