JPS6281815A - Analog-digital conversion circuit - Google Patents

Abstract

PURPOSE:To stabilize the multi-value information conversion by providing a circuit averaging a picture signal to the pre-stage of a reference level setting circuit of an A/D converter. CONSTITUTION:A picture signal Si outputted from a picture processing circuit 4 is averaged by an averaging circuit 10 and the a prescribed multiplication or addition processing by a level setting circuit 11, the one is given to the A/D converting circuit 1 as a high level reference value VH as it is, and the other is processed by a level converting circuit 12 and given to the A/D conversion circuit as a low level reference value VL. Thus, the reference voltage of the A/D converter 1 follows the level of the picture signal Si and since the voltage follows the background level fluctuation of the picture information, the multi-value information conversion by the A/D conversion circuit 1 is made stable. Further, in order to correct the delay in the processing time by the averaging circuit 10 or the level setting circuit 11, the picture signal Si inputted to the A/D conversion circuit 1 is retarded by the delay circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an A/D conversion circuit used in an image processing device such as a character recognition device, and particularly to an improvement in input level setting means for image information.

[Technical Background of the Invention] A conventional A/D conversion circuit of this type will be explained with reference to a circuit configuration block diagram shown in FIG. 6 and a signal waveform diagram shown in FIG. In FIG. 6, reference numeral 1 denotes an A/D conversion circuit, which generates a high level reference value VH set by a high level reference voltage generation circuit 2 and a low level reference value set by a low level reference voltage generation circuit 3. The image signal Si output from the image information processing circuit 4 is input within the range of the value VL, and is output after being converted into multivalued information.

In this case, the output (multilevel information) So is 5o-2"
It is expressed as S i −VL )/(V)I −Vt, ).

Generally, when character information is signal-processed by the image processing device 4, the character information Sa output as the image signal Si is
As shown in the figure, 7r-J (or "+
”) is output as a signal in a certain direction. Then, the ratio between the background level P and the level of the character information Sa becomes approximately constant.

[Problems with background technology]

By the way, the above-mentioned background level P is a light source and a camera.

It varies from cycle to cycle depending on the optical system such as the sensor, and this variation can become quite large depending on the optical system conditions.

Therefore, conventionally, in order to cope with any fluctuation in the background level P, the high level reference voltage Vo generated from the high level reference voltage generation circuit 2 and the low level reference voltage Vo generated from the low level reference voltage generation circuit 3 have been used. The input range of the image signal 3i determined by the voltage VL was set as a constant high level range. For this reason, it becomes difficult for the A/D conversion circuit 1 to extract the low-level character information 3a, and there is a possibility that the character information 3a may be converted into incorrect multi-value information. In this way, conventional A/D'! The conversion circuit 1 has poor non-circuit reliability, and a solution to this problem has been desired.

(Objective of the Invention) The present invention has been made in light of the above circumstances, and its purpose is to be able to follow changes in the background level of image information and to perform stable multi-value information conversion. An object of the present invention is to provide an A/D conversion circuit that can improve reliability.

[Summary of the invention]

The present invention averages image information by an averaging means, and multiplies the averaged image information by a certain ratio or adds a certain value to set a high-level reference value and a low-level reference value in a reference level range. This is how it was done.

Further, the present invention averages the image information by an averaging means, and multiplies the averaged image information by a certain ratio or adds a certain value to obtain a high level reference value and a low level reference value in the reference level range. At the same time, the image information is delayed by a predetermined time.

[Embodiments of the invention]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. Note that the same parts as in FIG. 6 are given the same reference numerals and detailed explanations will be omitted. In FIG. 1, reference numeral 10 denotes an averaging circuit, which averages the image signal s1 outputted from the image information processing circuit 4 by integral processing or the like. 11
is a level setting circuit which multiplies the image signal Si averaged by the averaging circuit 1o by a certain ratio (≧1) or adds a certain value (≦0) to set the high level reference value VH.
This high level standard value ■) is A/
The signal is applied to the D conversion circuit 1. Here, the above fixed ratio (≧
1) or a constant value (≧0) is the averaged image signal S
When the amount of change in i, that is, the character information 3a is a signal in the "-" direction, it is calculated and determined based on the decrease in the average value. On the other hand, 12 is a level conversion circuit, which is a constant ratio (≦
The low level reference value VL is obtained by multiplying 1) or adding a constant value (≦0), and this low level reference value Vt is provided to the A/D conversion circuit 1. here,
The above-mentioned fixed ratio (≦1) or fixed value (≦0) is determined based on the background level P in the image signal 3i or the level of the character information Sa.

Next, the operation of this embodiment will be explained. Assume now that the signal processing circuit 4 outputs an image signal indicated by 5i in FIG. This image signal 3i is supplied to the A/D conversion circuit 1 and also to the averaging circuit 10. Then, in the averaging circuit 10, the signals are averaged by, for example, slow integration processing. This averaged image signal S1
is multiplied by a certain ratio or added by a certain value determined based on the amount of change in the average value due to the text information Sa in the level setting circuit 11, and a high level reference value shown as 5i in FIG. 2 is set. and is input to the A/D conversion circuit 1.

On the other hand, in the level conversion circuit 12, the high level reference source VH set in the level setting circuit 11 is multiplied by a certain ratio or added by a certain value determined based on the background level P of the image signal 3i. A low level reference value indicated by Vt in FIG. 2 is calculated, and the A/D conversion circuit 1
is input.

As a result, in the A/D conversion circuit 1, the A/D conversion process of the image signal 3i is performed within the reference level range VH to VL corresponding to the background level P, and the A/D conversion process as shown by 5i in FIG. Value information is output.

As described above, in this embodiment, when the background level P is low, the reference level range is narrowed and the A/D conversion processing of the image signal 3i is performed, and when the background level P is high, the reference level range is widened. A/D conversion processing of image signal $1 is being performed. On the other hand, the ratio between the background level P and the level of the character information Sa is approximately constant. Therefore, according to this embodiment, A/D conversion is performed within a narrow reference level range for text information Sa with a low background level P and a small level,
For character information Sa with a high background level P and a large level, A/D conversion is performed within a wide reference level range.

As a result, even if the background level P varies greatly due to the influence of the optical system, the character information Sa can be easily retrieved, so the character information 3a can always be converted into accurate multi-valued information, improving reliability. .

Note that the present invention is not limited to the above embodiments.

Other embodiments of the present invention will be described below.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the present invention, and this embodiment corresponds to the case where character information Sa is processed as a constant signal in the "+" direction. In this embodiment, after the image signal S1 is averaged in the averaging circuit 20, the level setting circuit 21 multiplies the averaged image signal 3i by a certain ratio (≦1) or by a certain value ( ≦
6> is added to set the low level reference value VL, and A/
While supplying it to the D conversion circuit 1, the level conversion circuit 22 multiplies the low level reference II VL by a certain ratio (≧1) or adds a certain value (≧O) to calculate a high level reference value VH. and supplies it to the A/D conversion circuit 1. Here, the constant ratio or constant value in the level setting circuit 21 is the amount of change in the averaged image signal S1, that is, the character information 3
The constant ratio or constant value in the level conversion circuit 22 is determined based on the amount of increase in the average value due to a.
It is determined based on the background level P of .

In this way, also in this embodiment, the A/D conversion circuit 1 performs A/D conversion of the image signal S1 within the reference level range VH-VL that changes in accordance with the background level P of the image signal 3i. Therefore, the same effects as the first embodiment can be achieved.

FIG. 4 is a block diagram showing the configuration of a third embodiment of the present invention. In this embodiment, the high level reference value VH is set by the averaging circuit 10 and level setting circuit 11 similar to those in the first embodiment, and the low level reference value VL is set in the same way as in the second embodiment. Setting is performed using the same averaging circuit 20 and level setting circuit 21, and it goes without saying that the same effects as in each of the embodiments described above can be achieved.

FIG. 5 shows the third embodiment in which the image signal 3i from the image processing circuit 4 supplied to the A/D conversion circuit 1 is delayed by a delay circuit 30 for a predetermined period of time. By doing so, delays in processing time in the averaging circuits 10, 20 and level setting circuits 11, 21 can be corrected, and reliability can be further improved.

It goes without saying that various other modifications can be made without departing from the spirit of the invention.

〔Effect of the invention〕

As described in detail above, the present invention averages the #l@ information by an averaging means, and multiplies the averaged image information by a certain ratio or adds a certain value to obtain a high level standard in the reference level range. The value and low level reference value are set.

Further, the present invention averages the image information by an averaging means, and multiplies the averaged image information by a certain ratio or adds a certain value to obtain a high level reference value and a low level reference value in the reference level range. At the same time, the image information is delayed by a predetermined time.

Therefore, according to the present invention, it is possible to provide an A/D conversion circuit that can follow changes in the background level of image information, can perform stable multi-value information conversion, and can improve reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation in the same embodiment,
3 to 5 are block diagrams showing the configuration of the second to fourth embodiments of the present invention, and FIGS. 6 and 7 are block diagrams showing the configuration of the conventional example and signal waveform diagrams for explaining the operation. It is. 1...A/D conversion conversion circuit...image processing circuit, 10
゜20...Averaging circuit, 11.21...Level setting circuit, 12.22...Level conversion circuit, 3o...Delay circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 #! Figure 4 Figure 6

Claims (6)

[Claims] (1) In an A/D conversion circuit that converts image information into multivalued information within a predetermined reference level range, an averaging means for averaging the image information, and an image averaged by the averaging means. An A/D conversion circuit comprising: level setting means for multiplying information by a certain ratio or adding a certain value to set a high level reference value and a low level reference value in the reference level range. (2) The level setting means sets a high level reference value by multiplying the averaged image information by a constant ratio of 1 or more or adding a constant value of 0 or more, and sets the high level reference value by 1 A according to claim (1), characterized in that the low level reference value is set by performing level conversion by multiplying by the following constant ratio or adding by a constant value of 0 or less: /D conversion circuit. (3) The level setting means sets a low level reference value by multiplying the averaged image information by a constant ratio of 1 or less or adding a constant value of 0 or less, and sets the low level reference value by 1 A/ D conversion circuit. (4) In an A/D conversion circuit that converts image information into multivalued information within a predetermined reference level range, an averaging means that averages the signal level of the image information; and an averaging means that averages the signal level of the image information. level setting means for setting a high level reference value and a low level reference value in the reference level range by multiplying the image information by a certain ratio or adding a certain value; and a delay means for delaying the image information by a predetermined time. An A/D conversion circuit characterized by comprising: (5) The level setting means sets a high level reference value by multiplying the averaged image information by a constant ratio of 1 or more or adding a constant value of 0 or more, and sets the high level reference value to 1 or less. The low level reference value is set by converting the level by multiplying by a constant ratio or adding a constant value of 0 or less to set the low level reference value. D conversion circuit. (6) The level setting means sets a low level reference value by multiplying the averaged image information by a constant ratio of 1 or less or adding a constant value of 0 or less, and sets the low level reference value by 1 A/ D conversion circuit.