JP2577005B2 - Binarization processing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image scanner, which is one of input / output devices such as an information processing device, and in particular, optically reads and inputs an image on a document. The present invention relates to a binarization processing circuit suitable for a handy image scanner which outputs this as binarized information to the information processing apparatus or the like.

[Conventional technology]

2. Description of the Related Art Recently, an image (image) on a document is optically read and input into an information processing device such as a personal computer or a word processor, and the image is binarized and output to the information processing device. Skyana is now available.

As an image scanner of this type, CC
Using a line sensor such as D, the main scan is an electrical scan of the line sensor itself, and the sub-scan is a handy one performed by the operator moving the scanner body in a direction perpendicular to the direction in which the line sensor extends. FIG. 6 is a schematic configuration diagram showing an example of a handy image scanner, 20 is a main body case, 21 is a light source, 22 is a lens, 23 is a line sensor such as a CCD, and 24 is a line sensor. An encoder, 25 is an encoder roller, 26 is a processing / driving circuit, and 27 is a document.

In the figure, an image on a document 27 is illuminated by light from a light source 21, and the reflected light forms an image on a line sensor 23 through a lens 22.

A two-dimensional image on the document is read from the formed document image by main scanning by the transfer operation of the line sensor 23 itself and sub-scanning by moving the image scanner main body case 20 in the direction of the arrow shown in the figure. The control in the sub-scanning direction is performed based on an output signal from the encoder 24 when the roller 25 rotates.

The read image information may be directly transferred to an information processing device (not shown) and subjected to binarization processing in the information processing device. After the conversion process, the data is transferred to the information processing apparatus.

FIG. 7 is a block diagram showing an example of a binarization processing circuit according to the prior art, wherein 1 is a CCD line sensor, 2 is a timing generation circuit (including a CCD drive circuit), and 3 is a sample hold (S / H). Circuits 4, 5 and 5 are amplifiers, 6 is a comparator as binarization means, 15 is a dither reference voltage generation circuit, 16 is a contrast adjustment circuit, and 17 is a density adjustment circuit. In addition,
The contrast adjustment circuit 16 and the density adjustment circuit 17 are constituted by manually operated variable resistors (volume resistors).

In the figure, an image signal output from a CCD driven by a timing generation circuit 2 is sampled and held by a sample and hold circuit 3 by a sample pulse from the timing generation circuit 2. On the other hand, the dither reference voltage generation circuit 15 supplies a reference voltage (threshold) for dither processing to the comparator 6 through the amplifier 5. The comparator 6
Is binarized by comparing an image signal input from the sample hold circuit 3 through the amplifier 4 with a threshold value input from the amplifier 5, and performs dither processing.

This threshold is determined by the contrast adjustment circuit 16 and the density adjustment circuit.
It is changed by manually adjusting the 17 volumes.

[Problems to be solved by the invention]

Conventionally, when reading a picture or a picture drawn on a colored manuscript using such an image scanner, a test reading is performed prior to reading, and based on the image information obtained by this test reading, In view of brightness (density) and contrast, manual reading is carried out after manual density adjusting means is adjusted to obtain desired density and contrast.
The adjustment of the brightness and the contrast is performed by changing the threshold value of the comparator when binarizing the output signal of the line sensor.

The above test reading may not achieve the desired density and contrast only once, and depending on the image of the original, several test readings and adjustments may be required, making very cumbersome operations. However, there is also a problem that the quality of the image read by the operator varies.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, eliminate the need for manual adjustment of brightness and contrast, and make it possible for anyone to read an image easily and without failure. Another object of the present invention is to provide a conversion processing circuit.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a measuring means for measuring a maximum value and a minimum value of an image signal level output from a line sensor, and a holding means for holding the maximum value and the minimum value obtained from the measuring means. And threshold setting means for setting a plurality of thresholds between the maximum value and the minimum value.

[Action]

FIG. 3 is an explanatory view of the principle of the present invention.
The output of the D line sensor, (b) indicates a threshold value, and (c) indicates a binarized output.

As shown in the figure, the maximum value and the minimum value from the measuring means are obtained and held, and the range between the maximum value and the minimum value is divided into the number of gradations expressing halftone, and one line is A threshold is set, and dither processing is performed on the CCD output based on the threshold.

This threshold is changed periodically as shown in FIG. Brightness (density) and contrast can be changed by changing the offset and amplitude of the threshold voltage, respectively. All thresholds used to represent halftone are the maximum value of the image signal level (CCD sensor output). If the setting is made so as not to deviate from the minimum value and to divide the maximum value and the minimum value without shaking, appropriate brightness and contrast can be obtained.

FIG. 4 is a conceptual diagram showing 16 (2 ⁴ ) thresholds which divide the maximum value (MAX) and the minimum value (MIN) into 17 parts.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, wherein 1 to 6 correspond to the same reference numerals in FIG.
Denotes a D / A converter (including a contrast setting circuit), 8 denotes a density setting circuit, 9 denotes an A / D converter, 10 denotes a CPU, and 11 denotes a memory.

In this figure, in this embodiment, at the time of trial reading of a manuscript,
The output level of the CCD line sensor 1 of all the pixels (the area of the document) amplified by the amplifier 4 or the sampled pixels is converted into a digital signal by the A / D converter 9 and stored in the memory 11 via the CPU 10. The digital signal is subjected to arithmetic processing by the CPU 10 to set the brightest value (maximum value) and the darkest value (minimum value) of the document. The next set maximum value (MA
A signal (information) is sent from the CPU 10 to the density setting circuit 8 so as to create 16 gradation levels (thresholds) between X) and the minimum value (MIN), for example, as shown in FIG. And D / A
The contrast setting circuit of the A / D converter 7 sequentially arranges the 16 threshold levels in the pixel period in accordance with the dither reference pulse generated from the timing pulse from the timing generation circuit 2. The threshold level is changed 16 times for each pixel period, and the comparator 6 compares the output of the sample and hold circuit 3 amplified by the amplifier 4 with the 16 threshold levels for each pixel.
A binary signal obtained by dithering the output of the CCD line sensor 1 is obtained.

In this embodiment, calculation of the maximum value and the minimum value of the CCD output,
A threshold level is created and held using the CPU 10 and the memory 11.

FIG. 2 is a block diagram showing another embodiment of the present invention, in which the same reference numerals as in FIG. 1 correspond to the same parts, 12 is a maximum value (MAX) hold circuit, and 13 is a minimum value (MIN) hold circuit. The circuit, 14 is a subtractor, and 15 is the same dither reference voltage generating circuit as that given by the same reference numeral in FIG. 7, including a contrast setting circuit.

In this figure, in this embodiment, the maximum value of the CCD output (MA
X) and the minimum value (MIN) are detected by a peak hold circuit without using the CPU. MAX hold circuit 1 for holding
MIN hold circuit 13 for peak hold of 2 and minimum value
And the maximum value and the minimum value of the CCD output held by the sample hold circuit 3 and amplified by the amplifier 4 are held.

The maximum value (MAX) and the minimum value (MIN) held by the MAX hold circuit 12 and the MIN hold circuit 13, respectively, are subtracted by the subtractor 14 to calculate an interval between the maximum value and the minimum value.

The contrast setting circuit of the dither reference voltage generation circuit 15 is
The amplitude of the threshold level voltage divided by 17 (16 levels) is changed. For example, since the interval value between the maximum value and the minimum value is small for a document having a small contrast, the interval (amplitude) of the threshold level is also set to be small. Then, the density setting circuit 8 controls the amplifier 5 so that all threshold levels fall between the held maximum value and minimum value.

The threshold value thus controlled is supplied to the comparator 6 as a dither reference level, and is compared with the CCD output from the amplifier 4 to apply dither.

In each of the above embodiments, the maximum value (MA
X) and the minimum value (MIN) are measured and detected. Instead of using a CCD, for example, a phototransistor 31 such as a phototransistor as shown in FIG. , The minimum value may be detected.

The configuration in this case may be such that the output of the photo sensor is given to the CPU or the peak hold circuit in FIGS.

In the above description, the measurement of the maximum value and the minimum value is performed by performing a test reading prior to the reading of the document. However, the present invention is not limited to this. The density can be adjusted.

That is, for example, a 4 × 4 dither matrix 17
In the case of gradation expression, the maximum value and the minimum value of the first block (for four lines of the CCD) of the halftone are held, and the threshold value of the next block (the second block) is set using the values, and the dither is performed. At the same time, the maximum and minimum values of the block are held. Then, the threshold value of the third block is determined using the maximum value and the minimum value of the second block. That is, the threshold value of the Nth block is determined using the maximum value and the minimum value of the immediately preceding (N-1) block.

However, in this method, it is also necessary to deal with the case where there is a sudden change in the image of the original and to limit the amount of change in the threshold between the blocks so as to eliminate the unnaturalness of the image after the input processing. is there.

In order to implement this method, the maximum value and the minimum value may be measured by the CPU and the peak hold circuit shown in FIGS. 1 and 2, and the measurement may be performed in real time.

In the above example, the sample and hold circuit is provided after the CCD line sensor. However, when a line sensor having a sample and hold function is used, the sample and hold circuit in each embodiment may be omitted.

〔The invention's effect〕

As described above, according to the present invention, it is not necessary to manually adjust the density and contrast each time an image of a document is read by an image scanner, and a picture drawn on a colored document is not required. It is possible to read without quality deterioration, and if processing is performed using the CPU, it is also possible to automatically distinguish between binary reading and halftone image reading,
A binary processing circuit suitable for a handy image scanner with good operability can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a diagram for explaining the principle of the present invention, and FIG. FIG. 5 is an explanatory view of a setting example, FIG. 5 is an explanatory view showing another example of a document density detecting mechanism,
FIG. 6 is a schematic configuration diagram of a handy image scanner to which the present invention is applied, and FIG. 7 is a block diagram showing a conventional binarization processing circuit. 1 ... CCD line sensor, 2 ... Timing generation circuit,
3 ... Sample hold circuit, 4,5 ... Amplifier, 6 ...
Comparator, 7 D / A converter, 8 Density setting circuit, 9
... A / D converter, 10 ... CPU, 11 ... Memory.

Claims (1)

(57) [Claims] A line sensor, a rotary encoder, and a binarization processing circuit are provided in a main body case, and scanning of the line sensor itself is used as a main scan, and an output of the rotary encoder due to movement of the main body case is used as a sub-scanning reference signal. A binarization processing circuit of an image scanner that reads an image on a document and binarizes and outputs the same; a sample and hold unit that samples and holds an output of the line sensor for each pixel of the image; The brightest value of the image is measured as the maximum value from the signal held by the sample and hold means by the first reading as a trial reading of the entire image on the original, and the darkest value of the image is determined as the minimum value. A measuring means for measuring, and a predetermined number between the maximum value and the minimum value measured by the measuring means. Threshold setting means for setting a number of threshold levels; and for each period of the pixels held by the sample holding means by the second reading of the entire image on the document by the line sensor, the threshold setting means sets the threshold value. Threshold generating means for arranging and outputting the plurality of threshold levels, comparing the threshold level from the threshold generating means with the output of the sample and hold means, and outputting the output of the line sensor at each pixel. Binarizing means for binarizing so that the time ratio between the high level and the low level is different according to the level of the pixel, irrespective of the size of the brightness range of the image on the document,
A binarization processing circuit configured to obtain a binarized output automatically adjusted to a constant density and contrast in real time.