JP2718718B2 - Image reading device - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to an image reading apparatus, and more particularly, to an image reading apparatus that appropriately adjusts image reading density in accordance with document density. It is about.

(Prior Art) In recent years, various image reading apparatuses such as image scanners having a CCD image sensor or the like and inputting read image information to a computer have been proposed.

The conventional image reading apparatus has a changeover switch for changing the average density of the read image to an arbitrary average density. The changeover switch is operated by an operator of the image reading apparatus or automatically according to the density of the document. Can be appropriately switched.

Further, the conventional image reading apparatus has a so-called preset mechanism for adjusting the density of the read image to a standard density, and when a predetermined time has elapsed after reading of a series of images, When the switch is turned on, a preset mechanism is operated to reset the changeover switch to an intermediate density position, that is, a standard reading density.

(Problems to be Solved by the Invention) However, in the case where only an original having a high average density such as newspaper or colored paper or an original having a low average density such as writing with a pencil is always read by the image reading apparatus, the above-described method is used. Since the changeover switch is reset to the intermediate density position, that is, the standard reading density by the preset mechanism, the person reading the image must operate the changeover switch each time to reset to the appropriate reading density. Not
It was very annoying.

The present invention has been made in view of the above circumstances, and has as its object to provide an image reading apparatus that automatically and appropriately adjusts image reading density in accordance with the density of a document.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a means provided by the present invention is based on a method in which an optically read image is set based on a preset threshold value.
In an image reading apparatus for performing a binarization process, a means for reading the image, a density calculating means for calculating the density of the image each time the image is read by the reading means, and a nonvolatile memory for storing the density calculated by the density calculating means Storage means, means for reading the density stored in the non-volatile storage means, means for calculating a threshold value at the time of the next image reading by the reading means in accordance with the read density, and calculation processing by the calculation processing means Latch means for temporarily storing a value, threshold value setting means for setting the value temporarily stored in the latch means as a threshold value each time an image is read by the reading means,
Means for binarizing the image read by the reading means based on the threshold value set by the threshold value setting means, and at power-on, before the first image reading by the reading means, Assuming the previous density stored in the non-volatile storage means as the density of an image read by the reading means, setting a threshold value according to the assumed density, and reading the first image by the reading means Is carried out.

(Operation) In the image reading apparatus of the present invention, the binarization processing means binarizes the optically read image based on a preset threshold value and outputs the binarized image. Each time an image is read, its density,
For example, the image processing apparatus has density calculating means for calculating the average density for each scan, or the average density of the entire image, and the threshold setting means sets a threshold for the next reading in accordance with the calculated density. Further, the set threshold value is stored in the nonvolatile storage means. Therefore, the image reading density according to the density of the document to be read can be automatically and appropriately adjusted irrespective of the ON / OFF state of the power supply or the lapse of time.

(Example) Hereinafter, an example according to the present invention will be described in detail with reference to the drawings.

First, the configuration will be described with reference to FIG. 1. The scanner head 1 is connected to an inverting input terminal of a comparator 3 which is a binarization processing unit and to one input terminal of an adder 5. . The scanner head 1 is a CCD for sampling and optically reading the contents of a manuscript such as a newspaper.
It has an image sensor and the like, converts optical image information read by the CCD image sensor into an electric signal corresponding to the density of the image, and outputs the electric signal. The image information converted into the electric signal is supplied to an inverting input terminal of the comparator 3 and one input terminal of the adder 5.

The adder 5 is a density calculating means for calculating the average density of the image read by the scanner head 1, and information on the calculated average density is stored in the backup memory 9 via the register 7. This backup memory 9 is constituted by a nonvolatile memory,
Even in the event of a power outage, etc., the stored information on the average density is securely protected.

The microprocessor 11 is connected to each of the adder 5, the register 7, the backup memory 9, and the latch circuit 13. The microprocessor 11 has a control circuit, an arithmetic circuit, and the like, and executes an arithmetic process for setting a threshold used for a binary process described later to a more optimal value. Specifically, the information about the average density stored in the backup memory 9 is read, and a threshold value for the next reading is calculated according to the read average density. The calculated threshold value is calculated to be, for example, an intermediate value between an average value that can be regarded as black and an average value that can be regarded as white when performing the binarization process.

The threshold setting circuit 15 is connected to the microprocessor 11 via the latch circuit 13, and sets the value calculated by the microprocessor 11 as a threshold for performing the binarization processing as described above. The non-inverting input terminal of the comparator 3 is connected to the threshold setting circuit 15. A signal corresponding to the density of the image read from the scanner head 1, that is, a read signal, is given to the inverting input terminal of the comparator 3, and the value of the read signal is compared with the threshold value to determine whether black or white. The binarization process is performed on the indicated signal. For example, when the value of the read signal is equal to or larger than the threshold value, the L level signal is output as a binary signal indicating white. Conversely, when the value of the read signal is lower than the threshold value, the H level signal is output as a binary signal indicating black.

Further, the image reading apparatus according to the present invention has a function for finely adjusting the image reading density.

More specifically, the normal image reading apparatus has a five-stage changeover switch for manually switching the density of the read image, and has read densities G ₁ (light), G ₂ (lightly light), G ₃ (lightly light).
(Usually), G ₄ (slightly darker), so that it can be arbitrarily set corresponding to G ₅ (dark) the density of the original, and the like. Furthermore, in the present embodiment, the changeover switch, for example, in a state of being set from reading density G ₁ in a position to specify the _{G 2 (G 2> G 1} ), changes the threshold for the binarization processing described above If set, the concentration read in accordance with the threshold value in the range of G ₁ of G _2, for example in five steps, or is finely adjusted in a continuously variable.

 Next, the operation will be described with reference to FIG. 2 and FIG.

First, for example, the first image reading operation after power-on will be described with reference to FIG.

In step S1, for example, it is assumed that the average density of an image when a document is read is initially set to B when the power is turned on, and a threshold corresponding to the assumed average density B is set as an initial value. The value of the average density B is provisionally set in consideration of, for example, the average density of the previously read image.
In step S3, the original is read by operating the scanner head 1 in the initial state as described above. Step S5
Then, the average density A of the actually read image is
And the count value C is set to 1. The average density B is stored in the backup memory 9.

Next, the second and subsequent image reading operations will be described with reference to FIG.

In step S11, the average density B changed and set based on the average density of the image read for the first time is read from the backup memory 9, and a threshold corresponding to the average density B is set. In step S13, as described above, the document is read based on the threshold set in consideration of the average density of the previously read image. Assuming that the average density of the image read at this time is A, a new value of the average density B is calculated based on the average density A in step S15.

That is, as shown in the equation (1), a new average is calculated based on the changed average density B, the average density A of the image read in a state where the average density B is set, and the count value C. The density B is calculated. The calculated new average density B is stored in the backup memory 9. A binarization process is performed based on a threshold set according to the new average density B.

In step S17, the count value C is set to the maximum value Cmax, for example, 1
In the case of 6bit, it is determined whether it has reached 65535,
If the count value C is less than the maximum value, step S19
Then, the count value C is incremented by one.

Similarly to the above, in the third and subsequent image reading operations, the binarization process is performed based on the threshold set in consideration of the average density of the previously read image.

When a plurality of originals are read in this way and the count value C reaches the maximum value Cmax in step S17, the count value C is cleared, and the above-described average density B and threshold values for binarization processing are initialized. .

Although the maximum value of the count value C is fixed to a specific value in the above-described embodiment, for example, when reading a plurality of types of originals, the maximum value of the count value C is set for each type having the same density of the originals. With such a configuration, the threshold value for performing the binarization process can be set to a more appropriate value.

In the above-described embodiment, the threshold value for performing the binarization processing is uniquely set according to the average density B. However, not only the average density B but also other appropriate conditions, for example, the read image When the threshold value is set in consideration of a plurality of conditions by using the maximum value of the density and the like, the threshold value for performing the binarization process can be set more appropriately.

Further, the new average density B is calculated by the above-mentioned equation (1). However, the present invention is not limited to this, and for example, an arithmetic equation that takes into account the optical characteristics of the scanner head 1 is used. If the new average density B is calculated, the reliability can be further improved.

In an image reading apparatus provided with a plurality of scanner heads, if the backup memory 9 is configured to be shared by the respective scanner heads, the cost can be reduced.

Further, when reading is performed by switching to a document having a different density, if the storage contents of the backup memory 9 are transferred to another storage unit or the storage contents are reset,
The storage capacity of the backup memory 9 can be reduced.

[Effect of the Invention] As described above, according to the present invention, the threshold value for the binarization processing is set in consideration of the density of the read image, so that the density of the read image can be reduced. It can be adjusted automatically and appropriately.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are flowcharts showing the operation of FIG. 1 ... Scanner head 3 ... Comparator 5 ... Adder 11 ... Microprocessor 15 ... Threshold setting circuit

Claims (1)

(57) [Claims] 1. An image reading apparatus for binarizing an optically read image based on a preset threshold value, comprising: a means for reading the image; and a density of the image each time the image is read by the reading means. A non-volatile storage means for storing the density calculated by the density calculation means, and a density stored in the non-volatile storage means being read. Means for calculating a threshold value when reading an image; latch means for temporarily storing a value calculated by the calculation processing means; Threshold value setting means for setting as an image, and means for binarizing an image read by the reading means based on the threshold value set by the threshold value setting means. And when the power is turned on and before the first image reading by the reading means, the previous density stored in the nonvolatile storage means is assumed as the density of the image read by the reading means, An image reading apparatus, wherein a threshold value according to the assumed density is set, and the first image reading by the reading means is performed.