JPH06261211A - Image reader - Google Patents

Abstract

PURPOSE:To enable the excellent quality image reading by a simple operation by reading a white density sample and a black density sample, respectively and automatically setting read values as a full-white threshold level and a full-black threshold level. CONSTITUTION:The white part 7 of a full-white density sample 6 is read by the reading means 2 of an image reader 1, a read value is registered in a threshold level automatic setting means 3, a full-white threshold level is automatically set and a full-black threshold level is also automatically set via a full-black density sample 8. When the mode is set to a reading mode by an operation panel 5, a read image is quantized by a quantization means 4 by defining the thresholds set by the means 3 as a dynamic range and an excellent image reading can be performed by a simple operation.

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 in a digital copying machine, a facsimile machine, etc.
The present invention relates to an image reading apparatus capable of automatically setting an all-white threshold level and an all-black threshold level.

[0002]

2. Description of the Related Art A conventional method for quantizing an analog video signal will be described. The analog signal is quantized by an AD converter. At this time, a + white reference level (V + ref) is an all-white threshold level and a −reference input (V-ref) is an all-black threshold level. A document reading signal is input to the input (VIN), and the + reference input (V + ref) and the −reference input (V-re
During f), the signal input (VIN) is quantized at any time at the pixel clock timing. In this case, when reading the halftone image, as shown in FIG. 9, the + reference input (V + ref) and the −reference input (V-ref) are fixed.

However, in a halftone image such as a photograph, the density distribution is often biased toward a high density side or a low density side. In this case, if quantization is performed with a fixed threshold, white spots are likely to occur when the document density is biased to the white side (see FIG. 10), and conversely, when the document density is biased to the black side (FIG. 11). The blackish one is more likely to be crushed. Even if the white areas or the black areas are not crushed, the quantization range is biased to one side, which causes deterioration of the image. If the settings for the all-white threshold level and all-black threshold level are fixed levels, the above problems will occur.To alleviate them, provide several levels of all-white threshold level and all-black threshold level. There was also a method of selecting one of them according to the image.

[0004]

As described above, the level setting of the all-white threshold value and the all-black threshold value in the conventional image reading apparatus is fixed in advance or selected from a plurality of predetermined levels. I was trying to choose. However, among the above-mentioned conventional methods, when the level is fixed in advance, particularly when reading a halftone image such as a photograph, depending on the nature of the density of the original, if the density is biased toward the all-white side or all-black side, the video signal However, there is a problem in that high-quality image reading cannot be performed because halftone expression cannot be sufficiently performed due to wasteful quantization.

Further, even when a threshold is determined by selecting one level from a plurality of predetermined levels,
You have to operate from the operation panel, select one more level, scan the image, check whether it is good quality, and if it is not good, select another level again. Therefore, there is a problem that the operation becomes complicated, such as the same process must be performed. The present invention is
It is an object of the present invention to solve the above problems and provide an image reading apparatus capable of reading a high-quality image with a simple operation.

[0006]

In order to achieve the above-mentioned object, the present invention allows a white density sample or a black density sample to be directly read by an image reading device, whereby all white and all white in the quantization of the original read data. The density threshold of black is automatically set. As a specific means therefor, a means for reading a white density sample in advance, a means for automatically setting the read value as an all-white threshold level,
It has means for quantizing the read data of the document within the dynamic range range based on the automatically set all-white threshold level. Further, means for reading the black density sample in advance, means for automatically setting the read value as the all-black threshold level, and quantization of the read data of the document within the dynamic range range according to the automatically set all-black threshold level. Have means. Further, means for reading the all-white density sample and all-black density sample in advance, means for automatically setting the read values as the all-white threshold level and all-black threshold level, and the all-black threshold level automatically set and It has means for quantizing the read data of the original within the dynamic range range based on the all black threshold level.

[0007]

According to the present invention, the means for reading the white density sample in advance, the means for automatically setting the read value as the all-white threshold level, and the reading of the original within the dynamic range range according to the automatically set all-white threshold level. By providing a means to quantize data, if there is a bias toward the white side of the original, or if you want to set the specified density sample to the all-white threshold level, you can simply read the density sample and set the white threshold value. It becomes possible to register the level, and it is possible to easily and actually visually check the density to determine the all-white threshold value.
It can also be used for machine adjustment during production and field adjustment by service personnel.

Further, means for reading the black density sample in advance, means for automatically setting the read value as the all-black threshold level, and reading data of the original within the dynamic range range based on the all-black threshold level automatically set as described above. By providing the quantizing means, it is possible to set an arbitrary black threshold level simply by reading the density sample when the original has a density bias toward the black side.

Further, means for reading the all-white density sample and all-black density sample in advance, means for automatically setting the read values as the all-white threshold level and all-black threshold level, respectively, and the above-mentioned automatically-set all-black threshold value By providing a means for quantizing the read data of the original within the dynamic range of the threshold level and the all-black threshold level, both the all-white threshold level and the all-black threshold level can be set by simply reading the density sample. become,
The dynamic range at the time of quantization can be used effectively. In addition, both levels can be set with a single operation, which has the effect of saving time and effort.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram of an image reading apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an image reading device, 2 is a reading means for reading an all-white density sample, or an all-black density sample, and 3 is a read signal from the all-white density sample or all-black density sample read by the reading means 2. Threshold level automatic setting means for automatically setting the respective threshold levels based on 4; quantization means; 5; operation panel; 6 all white density samples; 7 white parts; 8 all black density samples; 9 The black part. Hereinafter, how the threshold level is registered in the image reading apparatus of the present invention will be specifically described.

(1) All White Threshold Level Registration Mode In this embodiment, the halftone expression has 64 gradations. The all white threshold level registration mode is designated by the operation port (operation panel 5) or switch. First, the + reference input (V + ref) level is set to a value higher than the normal document reading peak value (not saturated even in pure white). -The reference input (V-ref) level is set to ground (GND; 0V).

As a density sample, an original 6 having a portion 7 whiter than the background of the original is prepared. This white portion is registered as the all-white threshold value (see FIG. 2). In this case, it is better that the difference in density between the white portion and the background portion is large. After reading the density sample, the CPU analyzes the data and examines the distribution of 64 gradations, and as shown in FIG. 3, the first of all white side out of the noise (pixel) components existing in the reading area. The peak value of is the approximate value TWH of the all-white threshold value.

Based on this value, + reference input (V + re
f) Adjust the level. Attenuator AT for level adjustment
This is done by setting the reference value TWH in T1. The attenuator ATT1 can be adjusted bit by bit according to the reference value, but may be roughened according to the adjustment accuracy of the range.
The reference value set in the attenuator ATT1 is held unless the all-white threshold level registration mode is entered again. At the time of actually reading the original, the video signal is quantized on the basis of the above-mentioned all-white threshold level.

By doing so, when the original has a deviation toward the white side (the density offset on the black side is large), or when it is desired to set the specified density sample to the all-white threshold level, the density sample is simply sampled. The white threshold level can be registered simply by reading, and the total white threshold can be determined easily and visually by visually confirming the density. It can also be used for machine adjustment during production and field adjustment by service personnel.

(2) All-black threshold level registration mode The all-black threshold level registration mode is designated by the operation port (operation panel 5) or switch. First, the + reference input (V + ref) level is set to a value higher than the normal document reading peak value (not saturated even in pure white). -Reference input (V-ref) level is ground (GND; 0)
V).

As a density sample, an original 8 having a portion 9 that is darker than the background of the original is prepared. This black portion is registered as the all-black threshold value (see FIG. 5). In this case, it is better that the difference in density between the black portion and the background portion is large. After reading the density sample in the designated area, the CPU analyzes the data to examine the distribution of 64 gradations, and removes the noise (pixel) component existing in the reading area as shown in FIG.
The first peak value on the all black side is set to the approximate value TBL of the all black threshold value.

Based on this value, + reference input (V + re
f) Adjust the level. Attenuator AT for level adjustment
This is performed by setting the reference value TBL in T2. The reference voltage VR2 (when the attenuation is 0) of the attenuator ATT2 is (V
Set the maximum level of + ref) or about 1/2 of it as a guide. The reference value set in the attenuator ATT2 is
It is held until the all-black threshold level registration mode is entered again. At the time of actually reading the original, the video signal is quantized on the basis of the above-mentioned all-white threshold level. By doing this, if the original has a density deviation toward the black side (the density range on the white side is large), an arbitrary black threshold level can be set by simply reading the density sample for setting the black threshold level. It is possible.

(3) All-white threshold level and all-black threshold level continuous registration mode In this mode, TWH and TBL are set while simultaneously reading density samples for the target all-white and all-black threshold levels. First, the (V + ref) level is set to a value higher than the normal document reading peak value (not saturated even in pure white).
The (V-ref) level is set to ground (GND; 0V).
As the density sample, two-tone (two kinds of levels) of all-white level and all-black level, or one having a background of intermediate density is used. The whitest part of this density sample is registered as the all-white threshold, and the blackest part is registered as the all-black threshold. According to the registration mode operation instruction, first, all white threshold level registration is performed. The operation is the same as in the above-mentioned (1) all-white threshold level registration mode (see FIG. 7).

Next, all black threshold level registration is performed. In this case, it is the same as in the all-black threshold level registration mode of (2) above except that the (V + ref) level is used as a reference for the previously registered all-white threshold level (see FIG. 8). ATT1,
The reference value set in ATT2 is retained unless the registration mode is entered again. After these registrations, the actual document reading is performed. By doing so, both the all-white threshold level and the all-black threshold level can be set by simply reading the density sample, and the dynamic range at the time of quantization can be effectively used. Also, both levels can be set with a single operation, which saves time and effort.

(4) Fixed Threshold Mode In the above (1) to (3), the all-white threshold and all-black threshold are set by reading the density sample before the actual reading of the original. In many cases, a fixed threshold value of high is used. In this case, ROM beforehand
Several kinds of data are stored in a (read-only memory) or the like and can be set by the CPU (central processing unit) 10.
If this fixed threshold mode method and the methods of (1) to (3) above are combined as necessary, more versatile and flexible usage can be achieved.

If the white density sample 6 and the black density sample 8 used in the present invention are used for setting the all-white clamp level and the all-black clamp level, the original can be read with an arbitrary threshold value. There is also an effect that the read data can be processed by intentionally cutting (cutting down) above / below a certain density.

[0022]

EFFECTS OF THE INVENTION A white density sample or a black density sample is directly read by an image reading device, whereby the density thresholds of all white and all black in the quantization of the original read data are automatically set to a sample-dependent value. This is set. If the original is biased to the white side or if you want to set the specified density sample to the full white threshold level, you can register the white threshold level simply by reading the density sample. The density of all whites can be determined by actually visually confirming the density. It can also be used for machine adjustment during production and field adjustment by service personnel. Further, when the original has a density deviation toward the black side, an arbitrary black threshold level can be set by simply reading the density sample. Further, both the all-white threshold level and the all-black threshold level can be set by simply reading the density sample, and the dynamic range at the time of quantization can be effectively used. In addition, both levels can be set with a single operation, which has the effect of saving time and effort.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a read signal of an all-white density sample.

FIG. 3 is a diagram showing a distribution of read signals of all white density samples.

FIG. 4 is a circuit diagram for level adjustment.

FIG. 5 is a diagram for explaining a read signal of an all-black density sample.

FIG. 6 is a diagram showing a distribution of read signals of all black density samples.

FIG. 7 is a diagram for explaining a read signal of a white portion in a continuous registration mode of an all-white threshold level and an all-black threshold level.

FIG. 8 is a diagram for explaining a read signal of a black portion in a continuous registration mode of an all-white threshold level and an all-black threshold level.

FIG. 9 is a diagram for explaining a reading level of a halftone image.

FIG. 10 is an explanatory diagram when the density is high when quantized with a fixed threshold.

FIG. 11 is an explanatory diagram when the density is low when quantized with a fixed threshold.

[Explanation of symbols]

 1 image reading device 2 reading means 3 threshold level automatic setting means 4 quantizing means 5 operation panel 6 all-white density sample 7 white part 8 all-white density sample 9 black part 10 CPU (central processing unit)

Claims (3)

[Claims] 1. A reading means for reading a white density sample in advance, a threshold level automatic setting means for automatically setting the read value as an all-white threshold level, and a dynamic range range based on the automatically set all-white threshold level. An image reading apparatus having a quantizing unit for quantizing read data of a document. 2. A reading unit for reading a black density sample in advance, a threshold level automatic setting unit for automatically setting the read value as an all-black threshold level, and a dynamic range range based on the automatically set all-black threshold level. An image reading apparatus having means for quantizing read data of a document. 3. A reading means for reading an all-white density sample and an all-black density sample in advance, a threshold level automatic setting means for automatically setting the read values as an all-white threshold level and an all-black threshold level, respectively. An image reading apparatus comprising: a set all-black threshold level and a quantizing means for quantizing read data of a document within a dynamic range range based on the all-black threshold level.