JPH04320159A - Picture reader - Google Patents

Abstract

PURPOSE:To improve the copy productivity by correcting only one color among plural colors with a reflected luminous quantity from a reference white color board in the case of reading an original and correcting luminous quantity fluctuation through the multiplication of a prescribed correction value with other colors. CONSTITUTION:An analog gain at A/D conversion is matched (AGC) during warm-up before copy operation by an output of a CCD color sensor 8 reading a reference white color board 9. The AGC is implemented only to a green channel (G) severest in the characteristic of the visual sensitivity and the setting value is stored in a RAM. In the case of continuous copy, an output of the sensor 8 before the AGC input is corrected or the AGC setting is revised based on the processing of (G setting value X green/blue or green/red correction coefficient) with respect to blue and red channels. Thus, the digital read gradation number is constant for blue, green, red colors, the density fluctuation is suppressed, and one restoration of the read position of the board 9 is enough for one copy and the productivity is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus that scans a document area with an image reading optical system including a color reading sensor.

0002

[Prior Art] Image reading devices using color reading sensors take advantage of the digital feature that image processing is easy, and are far from the "trimming mode" in which only the center of the document is extracted and copied, and the registration of book documents. ``Book mode'' is well known, which allows you to copy only the first page.

In the case of a digital copying machine, a reference white plate (w
By providing a white reference plate, the sensor output of each color is corrected and color unevenness is eliminated.

FIG. 3 shows an example of this, and numeral 1 in the figure indicates the entire image reading device. The image reading device 1 is provided with, for example, a three-color blend light source 4 that illuminates the original 2 set on the platen glass 3, and the light from the light source 4 and the light reflected by the reflecting mirror 5 illuminate the original. Illuminate 2. The light reflected by the original 2 is collected by a rod lens array 6, passes through a correction filter 7, and is detected in each color by a CCD color line sensor 8. FIG. 5 shows an example of the characteristics of each sensor. In addition, since the reference white plate 9 is located outside the image area on the lead edge side, by correcting the sensor output for each color that reads the reference white plate 9, it is possible to ) can eliminate the effects of uneven sensor output. In the figure, 10 is a lamp heater.

[0005]

[Problem to be solved by the invention] Here, when making continuous copies in "trimming mode" or "book mode",
Unless it returns to the position directly below the reference white plate 9, it is not possible to obtain a copy with high image quality stability and no density fluctuations. In order to read each color of the original, B (blue), G (green), R (red), and K (black), four scans are required for one copy. The image reading device 1 must be returned to the position directly below 9. On the other hand, returning to the position where the reference white plate 9 is read requires a correspondingly longer scanning distance, which is negative in terms of copy productivity. Therefore, it is desirable to increase copy productivity without returning to the position of the reference white board 9 as much as possible, but if a change in the light amount of the exposure lamp occurs, it immediately appears as a change in density and a decrease in the number of read gradations.

In particular, when using a three-wavelength fluorescent lamp that is a blend of multiple phosphors and has spectral characteristics as shown in FIG. The number of reading gradations changed for each color, G (green) and R (red) (see FIG. 7).

SUMMARY OF THE INVENTION An object of the present invention is to improve copy productivity without reducing the number of read gradations for any of the reproduced colors without reading a reference white plate every time for each color.

[0008]

[Means for Solving the Problems] The present invention is an image reading device that uses a multicolor blending light source and corrects each color based on the amount of light reflected from a reference white plate prior to scanning the document. When reading, only one color out of the plurality of colors is corrected by the amount of light reflected from the reference white plate,
The present invention is characterized in that a correction means is provided for correcting light amount fluctuations by multiplying other colors by a fixed correction value.

[0009]

[Operation] In the present invention, when reading a certain document, only one color out of multiple colors is corrected by the amount of light reflected from the reference white plate, and for other colors, the light amount is multiplied by a certain correction value. Correct for fluctuations. This makes it possible to satisfy both the number of reading gradations and copy productivity.

0010

EXAMPLES The present invention will be specifically explained below based on examples. In the case of a digital copying machine, the analog gain at the time of A/D conversion is set based on the sensor output value read from the reference white plate 9. This is usually an operation to adjust the gain during warm-up before the copy operation (hereinafter referred to as AGC).
Implement. Since this AGC takes some time, it cannot be performed every time during a copy operation. The operation of this digital copying machine main body is shown in FIG. The important part here is the *1 AGC setting part. Here, AGC may be set for each color of B, G, and R, or only AGO may be stored in the memory, and calculation may be made from the ratio of AGO/AG1 after starting. FIG. 2 shows a detailed explanation of the document reading operation shown in FIG. 1.

In the present invention, AGC is performed only on the G (green) channel, which has the most severe visibility characteristics.
The set value is stored in RAM. In the case of continuous copying, only the AGC setting value for the G channel is memorized, and for the B and R channels, (G channel setting value) x (correction coefficient AG /AB or AG /AR
), the sensor output before AGC input is corrected or the AGC settings are changed. A flowchart of the above processing is shown in FIG.

[0012] This makes it possible to maintain the same number of gradations and suppress density fluctuations without changing the number of digitally read gradations for each color of B, G, and R after A/D conversion.

Moreover, it is only necessary to return to the position where the reference white plate 9 is read once per copy, and copy productivity can be greatly improved.

Table 1 and FIG. 4 show examples of the decrease in the B, G, and R light intensity of the light source depending on the number of copies.

[0015]

[Table 1]

[0016]

As explained above, according to the present invention, the number of times the reference white board 9 returns to the reading position is 1 per copy.
You only need to do this once, and copy productivity can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a flowchart showing processing in the present invention.

FIG. 3 is a schematic diagram showing an example of a document reading device.

FIG. 4 is a graph showing the light amount stability of the light source.

FIG. 5 is a graph showing the spectral characteristics of the sensor.

FIG. 6 is a graph showing the spectral characteristics of a light source.

FIG. 7 is a graph showing the spectral characteristics of a light source due to a decrease in light intensity.

[Explanation of symbols]

1 Image reading device, 2 Original, 3 Platen glass, 4 Light source, 5 Reflector, 6 Rod lens array, 7 Correction filter, 8 CCD color line sensor, 9 Reference white plate, 10 Lamp heater

Claims (1)

[Claims] Claim 1: In an image reading device that uses a multicolor blending light source and corrects each color based on the amount of light reflected from a reference white plate before scanning an original, when reading a certain original, the An image reading device characterized in that a correction means is provided for correcting only one of the colors using the amount of light reflected from the reference white plate, and for the other colors, correcting light amount fluctuations by multiplying by a fixed correction value. Device.