JPH01158878A - Picture reader - Google Patents

Abstract

PURPOSE:To convert an analog picture signal from an image sensor into a digital density data without quantization error by employing an A/D converter having a logarithmic characteristic by varying resistance of plural resistors dividing a reference voltage. CONSTITUTION:An analog input (Vin) is given in parallel with inputs of 255 sets of comparators COM 1-COM 255. A reference voltage to the comparators COM 1-COM 255 is a voltage division of LOG (logarithmic) characteristic resulting from a reference voltage (Vref) divided by plural resistors R1-R256. Then each comparator is active simultaneously in the application of a signal to the analog input and digital signals of 'H', 'L' level are outputted. The digital signal is converted into a desired code through a decoder DEC. Thus, the analog signal proportional to the reflected luminous quantity from the original is converted into the density data being the digital signal without quantization error.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device that digitally processes an image, such as an image reading device used in a digital copying machine, an image scanner, a FAX, and the like.

[Prior Art] A block diagram of a conventional image reading device is shown in FIG. FIG. 2 shows the waveforms of each part of this block diagram.

A document 2 on a document table glass 1 is illuminated by a light source 3, and the reflected light is imaged on a CCD 5 by a lens 4. C
The CD 5 outputs image information obtained by photoelectrically converting the image of the original document 2 in synchronization with a signal from the timing control section 6 . The output of the CCD 5 is inverted in phase by an amplifier 7, amplified, and then inputted to an S/H circuit 8.

The waveform sampled/held according to the signal from the timing control section 6 is reproduced by the next clamp circuit 9 into DC reproduction. This DC regenerated signal is sent to the A/D converter 10.
It is converted into a digital signal by human power.

FIG. 6 shows the human output characteristics of this A/D converter 10. The input/output characteristics are linear characteristics, and this A/D converted digital data is data proportional to the amount of light reflected from the original. The output of the A/D converter 10 is stored in a look-up table (L,
U, T) 20 to convert into density data. L, U,
The T2O conversion table is shown in FIG.

However, in conventional image reading devices with such a configuration, when converting the output of the A/D converter into U, T, the quantization error becomes large in areas where the manual digital data is small, and the density data The disadvantage of this method is that the error becomes large in regions with high concentrations, which are important for

[Object of the invention].

The present invention solves the above-mentioned conventional problems and provides an image reading device that can convert analog image signals from an image sensor during image reading into digital density data without quantization errors.

[Example] Hereinafter, a detailed explanation of an example of the present invention will be given based on the drawings.

FIG. 1 is a block diagram of an image reading device according to an embodiment. A document 2 on a document table glass 1 is illuminated by a light source 3, and the reflected light is imaged onto a CCD 5 by a lens 4. The CCD 5 outputs image information of the original 2 in synchronization with a signal from the timing control section 6. An example of the output signal from the CCD is shown in FIG. 2(A).

The output (A) of the CCD 5 is inverted in phase and amplified by the amplifier 7, resulting in a waveform as shown in FIG. 2(B). The output of the amplifier 7 is sampled/held by a circuit 8 based on a signal from the timing control section 6. This situation is shown in Figure 2 (C
).

This sampled/held waveform is reproduced by the next clamp circuit 9 as a direct current. FIG. 2(D) shows the waveform reproduced by direct current, in which the minimum level is set to O■.

This signal is then input to the A/D converter 10 having LOG characteristics and becomes a digital image signal.

A detailed block diagram of the A/D converter 10 of FIG. 1 is shown in FIG. 3.

FIG. 3 is a block diagram of a parallel comparison method (flash type), which is one of the methods for performing A/D conversion. 8 bit A
/D converter, analog input (Vin) is 25
Five comparators COM1~C0M255 are connected in parallel, each comparator COMI~C0
The reference voltage of M255 is a value obtained by dividing the reference voltage (Vref) using a plurality of resistors R1 to R256 according to LOG (logarithmic) characteristics.

When a signal is applied to the analog input, each comparator operates simultaneously and outputs "H" and "L" digital signals. This digital signal is converted into a desired code through a decoder D'EC.

Figure 3 shows the human output characteristics of the A/D converter in Figure 4.

That is, by determining the values of the resistors R1 to R256 in FIG. 3 so as to have the LOG characteristics in FIG. 4, it is possible to convert an analog signal proportional to the amount of reflected light from the original into density data, which is a digital signal. be. Note that R1-R256 in Figure 3, which determines the accuracy of this LOG characteristic, has good relative accuracy by making it by IC, resulting in a good LOG characteristic.
characteristics are obtained.

[Effects] As described above, the present invention can convert an analog image signal from an image sensor during image reading into a desired digital amount without any quantization error.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the image reading device of the present invention, FIG. 2 is a waveform diagram of each part to explain the block diagram of FIG. 1, and FIG. 3 is an internal block diagram of the A/D converter of the present invention. 4 is a human output characteristic diagram of the A/D converter in FIG. 3, FIG. 5 is a block diagram of a conventional image reading device, and FIG. 6 is an input/output characteristic diagram of the A/D converter in FIG. FIG. 7 is an input/output characteristic diagram of the look-up table shown in FIG. In the figure, 3 is a light source, 5 is a CCD, 10 is an A/D converter, R1-R256 is a resistor, and DEC is a decoder. 67th 7th W

Claims (1)

[Claims] In an image reading device that reads an image with an image sensor and outputs this image information as a digital signal, the analog image signal from the image sensor is converted into an analog image signal having logarithmic characteristics by changing the values of multiple resistors that divide the reference voltage.
An image reading device characterized by performing analog/digital conversion using a D converter.