JPH01122269A - Original reading device - Google Patents

Abstract

PURPOSE:To obtain an optimum image suitable for the type of an original and the characteristic of a display device, etc., by independently setting the black level of the original and the offset of the display device. CONSTITUTION:The set of an off-set value S0 can be executed with being completely independent from the set of a black level r0 of the original in a scanner side. Namely, when the scanner is assumed as S=S0 in case of (r)=r0, and S=Sm in case of (r)=rm, the displaying device can display all the ranges of 0-bm and further, there is no range where an original reflecting rate (r) can not be displayed. Thus, addition is executed with a voltage, which is adjusted through a voltage follower A5 by a VR, and the value is supplied to a differential amplifier A2. Accordingly, the 0-point (black level) of analog picture data Vin can be set by adjustment of the volume VR. According to the type of the original, or, according to the fond of a user, the range of the reading reflecting rate can be set.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a document reading device such as an image scanner or a digital copying machine.

[Prior art]

Conventionally, in document reading devices, the display device side (CRT
Although some have an adjustment function (such as ), most of them also change the gamma characteristics, which changes the color reproducibility and has the disadvantage that good images cannot be obtained.

〔the purpose〕

The present invention was made based on this background, and aims to optimize output image quality by always setting an appropriate black level depending on the type of document and the type of display device. With the goal.

〔composition〕

To this end, the present invention makes it possible to set the black level settings on the reading side and the black level settings on the display output side independently, thereby making it possible to set the optimal black level without changing the reproducibility of halftones. This is what I did.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an analog processing circuit of a general image scanner.

The optical image of the document formed on the light receiving surface of CCD 1 is
Read by 1. The CCD 1 is supplied with a timing pulse P for transfer and shifting, and thereby outputs a read image signal output OS and a dark output DO3. O8 and DO3 are differentially amplified by the buffer 2, resulting in an image signal from which reset noise of the CCD 1 and the like have been removed.

However, since it is still a pulse-like signal and has a DC offset, first perform zero clamping using SWI.
This determines the image signal 00 level and is usually CO
Switch SW1 at the timing immediately after the D reset pulse
This is done by turning on the switch SW2 and the capacitor Cs.
Turn SW2 ONL only when the output correctly indicates the image level (proportional to the reflectance of the original), c3
Make sure to charge it. Furthermore, the next FET3 is a buffer for receiving the voltage of Cs at high impedance. For the first time, the source output of FET3 becomes an analog image signal based on OV.

This voltage is further level-set to a predetermined voltage by the amplifier A1 and applied to the reference voltage terminal rf of the D/A converter 4. Shading correction data 5DATA, which will be explained later, is given to the digital input of the D/A converter 4, and the output vDA is V6A"Vo
DATA is given.

In stages A2 and A5, the dark current output D of CGD I
In order to compensate for O5, the dark current component is sampled and held using a signal DS that is turned ON only at the timing of the dummy pixel of CCD1 (a pixel that is shielded from light outside the effective pixel and outputs only the dark current component). Image signal VIIA
A true analog image signal from which the dark current component of the CCD 1 is also removed is obtained as the output Vin of A2.

On the other hand, the white reference output is sampled and held using the WS signal that is turned on at the timing when the CCD 1 is reading out the white reference plate portion, and the voltage whose level is adjusted by A3 and the variable resistor VR is obtained as the reference voltage Vref. Vref determines the full scale of the image signal. In the 0th stage, Vin is A/D converted by the A/D converter 5 in synchronization with the image clock VCLK using Vref as a reference (full scale). For the first time, a digital image signal is obtained as the output of the A/D. This A/D output is subjected to data conversion in the ROM 6 to obtain VDATA.

Digital image signal VDA obtained through the above process
The TA is subjected to processing such as MTF correction and density conversion as necessary, and then outputted from the image scanner together with a line synchronization signal (LSYNC) and an image clock (CLK).

FIG. 2 shows an example of the overall transfer characteristic from the original to the display. On the right side, the scanner output S for the original reflectance r represents the gamma characteristic of the scanner, and the display output S for S represents the gamma characteristic of the display device.

Assuming that the gamma characteristic of the scanner is a curve of A, and the display side is a curve of a mouth, the scanner output S is r = ro, which is 5-
O r-rlI and S-S.

The 0 display device output correspondingly becomes b at S-0.
−.

SS, b±b1, but in the range of 0≦S≦80, b=o in all cases, so if the original reflectance corresponding to So is rl, in the range of r0≦r:5r, Even if the scanner reads it, the display device cannot display it. In reality, CRTs have a tendency to form a curve similar to that of a mouth, although there are differences in degree.

In the present invention, it is possible to set the offset (iSo) on the scanner side completely independently of the setting of the black level r0 of the original.In other words, the scanner .

If you set it so that the display device is ob.

In other words, the gamma characteristic of the scanner is assumed to be a curve. On the other hand, if another CRT is connected and the curve is 2, if the scanner side remains at the curve C, a display output b0 will be generated corresponding to So, and the black on the scanner side will be gray on the display side. ``Black floating'' occurs.

In this way, it is better to be able to adjust the value of So in accordance with the display device.

FIGS. 3 and 4 show the adjustment mechanism on the scanner side.

FIG. 3 is a diagram explaining the setting method of ro, and the part A2 in FIG. 1 has been improved. The DS samples and holds the ONL and dark current components at the timing of the COD dummy pixel. ! The voltage is added to the voltage adjusted by VR via the voltage follower A5, and is applied to the differential amplifier A2. Therefore, by adjusting the volume VR, analog image data VinOO
You can set the point (black level). Manuscript type (I
The range of reading reflectance may be set according to the user's preference (edge photographs, printed originals, etc.) or according to the user's preference.

By the way, the reflectance is 2.0 for the silver halide photograph, and the printed manuscript (black area)
is about 1.5.

FIG. 4 shows 30 setting methods, which also correspond to FIG. ROM6 is a data conversion table,
The 0 display device is equipped with multiple conversion tables that provide a desired curve (for example, the curve shown in Figure 2) for the A/D output corresponding to r0≦r≦r. A desired curve can be obtained by creating 16 conversion tables in which So is changed according to the characteristics, and accessing the upper 4 bits of the ROM address using, for example, a 4-bit digit switch SW.

The black level adjustment on the reading side by VR and the offset adjustment by SW are completely independent and can be set separately from each other.

Although the above configuration has been explained using a single processing system, in the case of a plurality of processing systems such as a color scanner, it is easy to provide such a setting mechanism in each processing system.

〔effect〕

As described above, according to the present invention, the black level setting of the original and the offset setting of the display device can be performed independently, thereby achieving the optimal image quality that is adapted to the type of original, the user's preference, and the characteristics of the display device. This can be achieved with a simple configuration.

[Brief explanation of the drawing]

Figure 1 is the analog processing circuit diagram of the image scanner, Figure 2 is the analog processing circuit diagram of the image scanner.
The figure is a transfer characteristic diagram of the entire system, and FIGS. 3 and 4 are diagrams showing the adjustment mechanism on the scanner side. A2. A5... Black level setting means, SW... Offset setting means. Figure 2 Figure 3

Claims (1)

[Claims] A black level setting means for adjusting and setting the black level of the image signal according to the reflectance of the original, and an offset setting means for giving an offset to the image signal according to the characteristics of the display device. A document reading device characterized in that offset setting means can be individually adjusted and set.