JP2627219B2 - Image reading device - Google Patents

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, and more particularly to an automatic setting of a reading density value.

[0002]

2. Description of the Related Art FIG. 5 shows the appearance of a general image reading apparatus. At the upper part of the apparatus, an original picture table 2 made of a transparent material such as glass is provided. A light source and a light receiving element (not shown) are provided below the original table 2. When reading the original image, the original image is placed on the original image table 2 and the holding plate 4 is closed in the direction of arrow A. In such a state, light is emitted from the light source, and reflected light in the original image is received by the light receiving element to read an image. The read image is sent to an output device and output as an image having a gradation corresponding to the image signal. The inner surface (reflection surface) 4a of the holding plate 4 is usually white so as to reflect light well.

By the way, among various original images such as a bright original image and a dark original image, or an original image having a strong contrast or an original image having a weak contrast, the brightest original image is always used in order to always maximize the gradation gradation of the target image. It is preferable that the point (highlight point) and the darkest point (shadow point) match the upper limit and the lower limit of the range that can be expressed by gradation on the device side. For this purpose, it is necessary to obtain the density of the highlight point and the shadow point of the original image.

Conventionally, an operator looks at an original picture,
The highlight point and the shadow point were determined, and the density at that point was measured by a densitometer.

As described below, a method of automatically setting a highlight point density and a shadow point density by an image reading apparatus is also used.

First, provisional reading of an original image is performed. Next, a highlight point density and a shadow point density are determined from the read image data.

[0007]

However, the above-described conventional density setting has the following problems.
In the method in which the operator determines the highlight point density and the shadow point density by looking at the picture of the original image, there is a problem that it takes time to set the density. Furthermore, since the judgment is not fixed by the operator, there has been a problem that the set value fluctuates up and down.

Further, in the method of determining the highlight point density and the shadow point density by temporarily reading the original image, it is necessary to specify an effective reading range, and the operation is complicated. If the effective range of reading is not accurately specified, the highlight point density and the shadow point density may be determined, including the reflection surface 4a of the holding plate 4. Since the reflection surface 4a is generally white, it is recognized as a highlight point, and accurate density setting cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image reading apparatus which can solve the above-mentioned problems and can set a density value accurately with a simple operation.

[0010]

An image reading apparatus according to the present invention includes a light source for irradiating light toward an original image, a holding plate having a reflection surface for holding the original image and reflecting light from the light source, an original image, and a light source. A light receiving element for receiving light reflected from the reflection surface of the holding plate and converting the light into an image signal; performing a tentative reading before performing the actual reading of the original image;
And an image reading apparatus that performs gradation adjustment at the time of main reading based on the density distribution of the reflection surface of the holding plate, wherein the density value of the reflection surface of the holding plate is higher than the density of the brightest point of the original image. It is characterized in that the density is lower than that of the dark spot.

[0011]

In the image reading apparatus according to the present invention, the density value of the reflection surface is set to be higher than the density which appears best as the brightest point of the original image, and lower than the density which appears best as the darkest point. Therefore, even if the effective range of reading is not specified at the time of provisional reading and provisional reading is performed without the reflection surface of the holding plate being indistinguishable from the original image, there is no possibility of being mistaken as the brightest point or darkest point of the original image.

[0012]

FIG. 5 shows the appearance of an image reading apparatus according to an embodiment of the present invention. At the upper part of the apparatus, an original picture table 2 made of a transparent material such as glass is provided. A light source and a light receiving element (not shown) are provided below the original table 2. When reading the original image, the original image
And the holding plate 4 is closed in the direction of arrow A. In such a state, light is emitted from the light source, and reflected light in the original image is received by the light receiving element to read an image.
The read image is sent to an output device and output as an image having a gradation corresponding to the image signal.

In this embodiment, the reflecting surface of the holding plate 4
The density value of 4a is about 0.9. Here, the density value D refers to a value represented by the following equation.

D = -logT where T is a reflectance, and if T = 1, perfect reflection, T
= 0 indicates complete non-reflection.

As is clear from the above equation, the density D value is
Brighter points are smaller and darker points are larger.

FIG. 1 schematically shows reading of an original image by an image reading apparatus according to one embodiment of the present invention. The original picture 6 is placed on the original picture stand 2, and the holding plate 4 is further placed thereon. The reflection surface 4a of the holding plate 4 serving as the background of the original image 6 has a density value of D = 0.9 as described above.

A linear light source 8 is provided below the original picture table 2 and emits light toward the original picture 6. The light reflected by the original image 6 is received by the CCDs 14 arranged in a row via the reflecting mirror 10 and the optical system 12. Thus, one line of image data is converted into an analog electric signal. The linear light source 8, the mirror 10, the optical system 12, and the CCD 14 scan the original image 6 in the direction of arrow B to obtain image data of the entire original image 6.

The setting of the density value according to this embodiment will be described below. The setting of the density value is performed by performing temporary reading (pre-scan). The image data read by the CCD 14 in the temporary reading is converted into digital data by the A / D conversion circuit 16. Thereafter, shading correction is performed by a shading correction circuit 18 to correct the characteristics of the CCD 14 and the like. The corrected data is supplied to the maximum / minimum value holding circuit 20. That is, in the temporary reading mode, the switch 22 is switched to the maximum value / minimum value holding circuit side.

The maximum / minimum value holding circuit 20 fetches the given data, determines data indicating the lowest density (data at a highlight point) and data indicating the highest density (data at a shadow point), and stores the data. Circuit.

FIG. 2 shows an example of the maximum value / minimum value holding circuit 20. The data input from the terminal 30 is compared with the comparison circuits 32 and 34
Given to. In the comparison circuits 32 and 34, the storage circuit 36
Is compared with the input data to determine whether or not to update the contents of the storage circuits 36 and 38. At first, the input data is left
Stored at 6,38. When the next data is input, the comparison circuit 32 compares the data with the data stored in the storage circuit 36. If the input data is larger, the data in the storage circuit 36 is updated. Further, the comparison circuit 34 compares the data with data stored in the storage circuit 38. If the input data is smaller, the data in the storage circuit 38 is updated. If the above operation is performed for all data,
The maximum value is obtained from the storage circuit 36, and the minimum value is obtained from the storage circuit 38.

The maximum value obtained as described above is the data of the highlight point, and the minimum value is the data of the shadow point. These two data are given to the gradation conversion circuit 24.
The gradation conversion circuit 24 determines an optimal function for converting the gradation of the image data based on the gradation data.

In this reading, the switch 22 is switched to the gradation conversion circuit 24, and the image is read.

Incidentally, the readable range of the CCD 14 is generally larger than the original image 6. FIG. 3 shows this relationship. It can be seen that the readable range 5 is wider than the original image 6. The reflection surface 4a is formed wider than the readable range 5.

In the state shown in FIG. 3, when provisional reading is performed for the entire readable range 5, a portion 7 where the original image 6 does not exist is provided.
(Hatched portion) is also a target for determining the maximum value and the minimum value. But,
In this embodiment, the density value D of the reflection surface 4a is set to about 0.9. In a typical original image, the highlight point density value is sufficiently lower than 0.9, and the shadow point density value is sufficiently higher than 0.9. Therefore, even if provisional reading is performed for the entire readable range 5 to determine the maximum value and the minimum value, there is no risk of erroneous determination. That is, there is no possibility that the portion 7 where the original image 6 does not exist is recognized as a highlight point or a shadow point. Therefore, unlike the related art, there is no need to set the effective reading range, and the operation is not complicated.

FIG. 4 shows the results of measuring the density at the highlight point and the density at the shadow point for 50 original images.
The horizontal axis is the density D, and the vertical axis is the number of appearances. As is clear from this distribution chart, when the concentration D is between 0.7 and 1.1,
There are no highlight points and no shadow points. Therefore,
It is preferable that the density value of the reflection surface 4a of the holding plate 4 be in the range of 0.7 to 1.1.

If the density value of the reflection surface 4a is in the range of 0.4 to 1.4, the density can be set for almost 90% of the original images without any problem.

In the above embodiment, the light receiving element is C
Although CD14 is used, other photoelectric conversion elements may be used.

Although the maximum and minimum value holding circuit 20 is constituted by a logic circuit, it may be constituted by a CPU and a memory.

In the above-described embodiment, the original 6 is placed on the original stand 2 and the holding plate 4 is pressed from above. However, the original image table 2 may be omitted by adsorbing and fixing the original image 6 to the holding plate 4 by electrostatic adsorption or vacuum adsorption.

[0030]

According to the image reading apparatus of the present invention, the density value of the reflection surface is set to be higher than the density which appears best as the brightest point of the original image, and to be lower than the density which appears best as the darkest point. Therefore, at the time of provisional reading, the highlight point density and the shadow point density can be set accurately from the density distribution without specifying the effective reading range.

That is, it is possible to provide an image reading apparatus capable of setting a density value accurately with a simple operation and performing tone adjustment at the time of main reading based on the density value.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a maximum value / minimum value holding circuit.

FIG. 3 is a diagram showing a relationship between the size of a readable range 7 and the size of an original image 6;

FIG. 4 is a diagram showing a distribution of highlight point density values and shadow point density values for 50 original images.

FIG. 5 is a diagram illustrating an appearance of a general image reading apparatus.

[Explanation of symbols]

 2 ... Original table 4 ... Holding plate 4a ... Reflective surface 6 ... Original 8 ... Linear light source 14 ... CCD

Claims (1)

(57) [Claims] 1. A light source for irradiating light toward an original image, a holding plate for holding the original image and having a reflection surface for reflecting light from the light source, and receiving reflected light from reflection surfaces of the original image and the holding plate. comprising a light receiving element for converting an image signal, performs a temporary read before performing the read book original, gradation during the reading on the basis of the density distribution of the reflected surfaces of the obtained original image and the holding plate by provisional reading In the image reading device for performing the adjustment, the density value of the reflection surface of the holding plate is higher than the density which appears best as the brightest point of the original image, and is lower than the density which appears best as the darkest point. Image reading device.