JPH0614686B2 - White balance adjustment device for color scanner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a white balance adjustment device for a color scanner that adjusts the output level of each color image signal read by color separation by a color scanner on a white reference.

2. Description of the Related Art Generally, when image information of a color original is color-separated into R, G, and B color elements and read and each color image signal is output, reproduction is performed based on each output color image signal. In order to improve the color reproducibility of the formed image, it is necessary to adjust the output level of each color image signal on the basis of white.

At that time, conventionally, the voltage level of each color image signal output of the color scanner is manually set to achieve white balance, but the spectral distribution characteristics change due to deterioration of the light source in the color scanner, changes in ambient temperature, etc. Then, the white balance is lost, and it is necessary to reset the manual setting each time.

Further, conventionally, the gain control signals R ', B'of the R, B signals are equal to the G signals based on the R, G, B signals when a white subject is imaged in advance by a color TV camera. After controlling the gain of each R and B signal to obtain white balance, it is always zero according to each difference signal between the R'and B'signals and the G signal at the time of normal image pickup thereafter. R'by a negative feedback loop such as
Each gain of the B'signal is controlled to readjust the white balance (Japanese Patent Laid-Open No. 58-1426).
No. 93). However, if such a means is adopted, the white balance is set with reference to each of the R, G, and B image signals when a white subject is imaged. Therefore, depending on the white subject, the white balance reference is set. There is a problem that is changed.

The present invention has been made in consideration of the above points, and color-separates color image information when an original surface of an original placed on an original table is optically scanned to separate a plurality of line image sensors for each color. In a color scanner that outputs a read color image signal by, a white reference plate provided outside the reading area of the document, and provided for each line image sensor,
An A / D conversion circuit for A / D converting the color image signal based on a reference value at the time of reading the original document, and the line image sensor are provided for each line image sensor. An object of the present invention is to automatically and easily perform white balance adjustment in a color scanner by including a control circuit that controls the output of each line image sensor when scanning to the reference value.

Configuration Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, as shown in FIG. 1, when the surface of the original 2 placed on the contact glass 1 of the original table is linearly illuminated in the main scanning direction by the light source 3, the reflected light is color-separated by the optical system 4. Then, for example, the color image information of the original having the R, G, and B components separated into the respective colors is sequentially read in the sub-scanning direction by the line image sensors 51, 52, and 53 in which a CCD for each pixel is arranged for one line. In the color scanner, a white reference plate 10 is provided on the contact glass 1 outside the reading area of the original 2, and each line image sensor 51 when the white reference plate 10 is optically scanned before reading the original 2. The white balance is set according to the outputs of 52 and 53. It should be noted that the color scanner may be any one of a scanning system by fixing the platen and moving the optical system or a scanning system by moving the platen and fixing the optical system. As shown in FIG. When a method of feeding the sheet-shaped original 2 in the sub-scanning direction with both the base and the optical system fixed, the pressing surface of the pressing plate 11 for pressing the original may be white, and it may also be used as a white reference plate.

FIG. 3 shows a concrete example of the configuration of the white balance adjusting apparatus for a color scanner according to the present invention, in which the color image separated R, G, B output from the line image sensors 51, 52, 53 in pixel units. Image signal S (R) of
S (G) and S (B) are respectively converted into AD converters 61, 62,
When binarizing by 63, the respective image signals S (R), S
(G), S (B) voltage variable circuits 71, 72, 73 for respectively varying the voltage levels, and the respective voltage variable circuits 7
1, 72, 73 output voltage and AD converters 61, 62, 6
3 and the reference voltages Vref of 3 respectively, and when the hold-off signal Hoff is given when the error amplifiers 81, 82 and 83 which generate an output voltage of the voltage control which is proportional to the difference if the two voltages are not equal, The variable control voltage output from each error amplifier 81, 82, 83 at that time is sent to the control terminal of each voltage variable circuit 71, 72, 73 as it is, and when the hold-on signal Hon is given. The error amplifiers 81, 82, and 83 are configured by holding circuits 91, 92, and 93 that hold the variable control voltages respectively output. The reference voltage Vref in this case is fixed. As for the hold-on and off signals Hon and Hoff, a hold-off signal Hoff is issued from a scanner controller (not shown) when the white reference plate 10 is optically scanned in the color scanner shown in FIG. The hold-on signal Hon is output from the scanner controller when the optical scanning of the white reference plate 10 is completed.

However, in the case of such a structure, the manuscript 2
Each time the color image information is read, each of the line image sensors 51, 52, 5 when the white reference plate 10 is optically scanned prior to reading the color image information.
3 are sent to the voltage variable circuits 71, 72, 73, respectively, and there the hold circuits 91, 92, 93 are turned off, and the voltage variable circuits 71, 72, 73 are turned off via the error amplifiers 81, 82, 83. Output voltage is the reference voltage V
The voltage is adjusted to be equal to ref and white balance is taken. Next, when the hold circuits 91, 92, 93 are turned on by the end of the optical scanning of the white reference plate 10, the variable control voltages in the error amplifiers 81, 82, 83 when the white balance is maintained are held respectively. The color image signal S read out by separating the respective colors of the original 2 is read in the state where the variable control voltage is held.
The voltage levels of (R), S (G), and S (B) are adjusted by the voltage variable circuits 71, 72, and 73, and the level-adjusted color image signals S '(R), S' (G),
S '(B) is given to the AD converters 61, 62 and 63, respectively, and binarized. Therefore, the AD converters 61 and 6
From 2, 63, R, G, and B binarized with white color balance and good color reproducibility every time the original 2 is read.
The color image signals S ″ (R), S ″ (G), and S ″ (B) are obtained.

FIG. 4 shows another embodiment of the present invention. In this case, the color image signals S (R), S (G), S (B) read by the respective line image sensors 51, 52, 53 are When binarizing by the AD converters 61, 62 and 63 through the amplifiers 121, 122 and 123 respectively, the line image sensors 51, 52 and 53 when the white reference plate 10 is optically scanned prior to reading the original. The output voltages of the amplifiers 121, 122, 123 at the time of the output of are held in the peak hold circuits 131, 132, 133, respectively,
The voltage values Vref (R), Vref (G), respectively held in the respective peak hold circuits 131, 132, 133,
Vref (B) is used as a reference voltage for the AD converters 61, 62, 63, and then each line image sensor 51, 5
The color image signals S (R), S (G), and S (B) of the original 2 read by the reference numerals 2, 53 are respectively AD-converted.

However, in the configuration as described above, in each AD converter 61, 62, 63, the reference voltage Vref
Input voltage up to (R), Vref (G), Vref (B)
When the D conversion is performed, the reference voltages Vref (R), Vref (G), and Vref (B) in the AD converters 61, 62, and 63 are set according to the respective input voltage levels. Color image signals S (R), S (G), S output from 51, 52, 53, respectively.
Even if the voltage level of (B) is different, the AD converter 61,
The outputs 62 and 63 are equal on the output side, resulting in white balance and binarized R, G, and B color image signals S (R), S (G), S with good color reproducibility.
(B) will be obtained.

Effect As described above, according to the present invention, color image information obtained by optically scanning the document surface of a document placed on a document table is color-separated, and a color is read by a plurality of line image sensors for each color. In a color scanner that outputs an image signal, a white reference plate provided outside the reading area of the original and a line image sensor are provided for each of the line image sensors. An A / D conversion circuit for D / D conversion and a control provided to be provided for each of the line image sensors so that the output of each line image sensor when the white reference plate is optically scanned before reading the original document becomes the reference value. By providing the control circuit for controlling the white balance, it is possible to automatically and easily perform white balance adjustment in the color scanner.

[Brief description of drawings]

FIG. 1 and FIG. 2 are simplified diagrams each showing a configuration example of a color scanner according to the present invention, and FIGS. 3 and 4 are block configuration diagrams showing an embodiment of a white balance adjusting device for a color scanner according to the present invention. Is. 2 ... manuscript, 3 ... light source, 4 ... optical system, 51, 52,
53 ... Line image sensor, 61, 62, 63 ...
AD converter, 71, 72, 73 ... Voltage variable circuit 81,
82, 83 ... Error amplifier, 91, 92, 93 ... Hold circuit, 10 ... White reference plate, 11 ... Pressure plate, 12
1, 122, 123 ... Amplifier, 131, 132, 13
3 ... Peak hold circuit

Claims (2)

[Claims] 1. A color scanner for color-separating color image information obtained by optically scanning a document surface of a document placed on a document table, and outputting color image signals read by a plurality of line image sensors for each color. A white reference plate provided outside the reading area of the original and an A / D converter provided for each of the line image sensors for A / D converting the color image signal based on a reference value when reading the original. And a control circuit which is provided for each line image sensor and which controls the output of each line image sensor when the white reference plate is optically scanned before reading the original document so as to make it the reference value. A white balance adjustment device for a color scanner. 2. The white balance adjusting device for a color scanner according to claim 1, wherein the control circuit is a peak hold circuit.