JPH04119755A - Picture read method and picture reader - Google Patents

Abstract

PURPOSE:To improve the S/N by applying preliminary scanning to each original to obtain a margin for a light receiving quantity of a opto-electric transducer element at a brightest part in a trimming region of the original to be read and applying main scanning to the original while the light receiving quantity of the opto-electric transducer element till the margin of the light receiving quantity is consumed out. CONSTITUTION:A light receiving quantity margin detection means 32 is operated after preliminary scanning and a highlight level at the brightest part in a trimming region of an original 6 to be read is obtained. A light receiving quantity adjustment means 36 adjusts the light receiving quantity of a photo multiplier 10 so that the light receiving quantity margin of the photo multiplier 10 at the brightest part of the original 6 to be read is consumed out at the main scanning based on the obtained light receiving quantity margin. Thus, even when the original is relatively dark in the highlight level, the light receiving quantity of the photo multiplier 10 is increased at the main scanning, then the rate of picture signals is increased and the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading method and an image reading device, and particularly relates to reducing noise of a photoelectric conversion element.

[Conventional technology] A conventional cylinder type image reading device is shown in FIG.

This image reading device includes a transparent cylindrical cylinder 2 and a pickup unit 4. A document 6 such as a film is wound on the cylinder 2 . The pickup unit 4 includes a white light source 8, a photomultiplier (hereinafter referred to as a photomultiplier) 10 as a photoelectric conversion element, and optical components such as a reflection mirror 12, a condensing lens 14, a pickup lens 16, and a filter 18. System equipment is provided.

The light projected from the light source 8 is reflected by the reflecting mirror 12 and focused onto the original 6 by the condensing lens 14 . A portion of the light that has passed through the original 6 is taken into the pickup unit by the pickup lens 16 and guided onto the photomultiple 10 via the filter 18 and other unillustrated apertures, mirrors, and the like. As a result, Photomaru 10
An image signal corresponding to the brightness/darkness of the corresponding position of the original 6 is output.

A motor 20 rotates the cylinder 2 in the direction shown by an arrow 22. At this time, the pickup unit 4 is moved in the direction of arrow 26 by the motor 24 driven in synchronization with the motor 20. Therefore, the original 6 on the cylinder 2 is scanned in a spiral manner, and image signals for the entire original 6 are sequentially output from the photomultiplier 10.

Note that when the original 6 is photographic paper or the like, the original 6 is reflected and illuminated from a light source (not shown) provided near the pickup lens 16. And pickup lens 1
6 to collect the reflected light.

In addition, when reading a color image, the original 6 is illuminated with a white light source and the transmitted light or reflected light is e.g.
, GSB components, and a photomultiplier is provided for each color component to obtain a signal for each component.

Alternatively, the light sources 8 for R, G, and B components may be turned on sequentially, or the RSG and B color filters may be replaced to obtain signals for each component using a single photomultiple 10.
, G, and B components are turned on at the same time, and a photomultiplier 10 is provided for each color component to obtain a signal for each component.

In addition to the cylinder-type image reading devices described above, there are also planar laser scanning type devices and devices that use a one-dimensional photoelectric conversion element such as a CCD.

Now, with photoelectric conversion elements such as photomultipliers and CCDs, it is desirable that as the amount of received light increases, the output voltage also increases proportionally, as shown by line 2 in FIG. However, due to dark current and the like, the output of the photoelectric conversion element includes a fairly constant noise voltage vN regardless of the amount of received light (■ in FIG. 3).

Furthermore, when the amount of received light exceeds a certain range, so-called clipping occurs in which linearity is lost, and even if the amount of received light increases, the increase in output voltage slows down gradually or sharply (■ in FIG. 3).

For this reason, in conventional image reading, reading is performed using the following method.

The following discussion will focus on reading a positive original.

First, the reading device is adjusted in accordance with the case where the highlight level, which is the brightest part of the document to be read, is the highest possible. In other words, the one with the highest highlight level is
If the document is a transparent document, this is a so-called transparent portion with 100% transmittance. If the document is a reflective document, it is a pure white portion with 100% reflectance. When the brightest part of this document is read, the amount of light emitted by the light source is adjusted so that the output of the photoelectric conversion element reaches the specified maximum output voltage V1.1 with some margin from the saturated output. Set to constant. Note that the sensitivity of the photoelectric conversion element is constant unless it is a -variant. Therefore, for any document, the amount of light received by the photoelectric conversion element is limited to the maximum amount of light received at the brightest part of the document, and the output voltage is limited to the specified maximum output voltage. Limited to within a. In addition, 1. at this time. The difference between the maximum received light amount ■ゎゎ,8, that is, I, , , , -Ib, is called the received light amount margin. As a result, the photoelectric conversion element outputs an image signal corresponding to the brightness and darkness of the original 6 without clipping distortion.

[Problems to be solved by the invention] However, in the conventional image reading method and image reading device,
The following problems arise.

The highlight level of the brightest part of a document to be read differs from document to document. For this reason, if the highlight level is adjusted to the highest possible level and a typical document with a low highlight level is read, the amount of light received by the photoelectric conversion element in the brightest area will be low (I in Figure 3). , the output voltage also becomes lower (V, , in Figure 3). On the other hand, the noise voltage vN output from the photoelectric conversion element remains constant regardless of the output voltage. Therefore, for a document that is relatively dark at the highlight level, the image signal to noise signal ratio (S/N ratio) will deteriorate.

An object of the present invention is to provide an image reading method and an image reading apparatus that solve the above-mentioned technical problems and improve the S/N ratio.

[Means for Solving the Problems] In order to solve the above-mentioned technical problems, the present invention has the following configuration.

That is, the image reading method of claim (1) includes pre-scanning each document before the main scan,
The method is characterized in that the margin for the amount of light received by the photoelectric conversion element at the brightest part within the trimming area of the document to be read is determined, and the main scan is performed while increasing the amount of light received by the photoelectric conversion element until there is no margin for the amount of light received at the brightest part. In the image reading method of claim (2), in the case of color separation, pre-scanning is performed in advance before main scanning, and the brightest part within the trimming area of the document to be read is scanned in advance for some or all of each color component. The image reading method according to claim 3, characterized in that the main scan is performed in a state in which the amount of light received by the photoelectric conversion element is increased until there is no margin in the amount of light received by the photoelectric conversion element at the brightest point. is claim (1) or (
In the image reading device according to claim 2), the image reading device according to claim 4 is characterized in that in the main scan, the output of the photoelectric conversion element is reduced by the amount that the light receiving aperture is raised. It has a light source that performs transmitted illumination or reflected illumination with a constant amount of light during main scanning, and a photoelectric conversion element that receives transmitted light or reflected light from the illuminated document and outputs an image signal according to the received light amount. This device reads the image of light as an electrical image signal corresponding to the brightness and darkness of the light, and during prescanning, the brightest part of the image signal output from the photoelectric conversion element in the trimmed area of the document to be read is read. A received light amount margin detection means detects the level of the image signal of the photoelectric conversion element and determines the received light amount margin of the photoelectric conversion element, and from the determined received light amount margin, the received light amount margin of the photoelectric conversion element at the brightest part of the document to be read is determined during main scanning. The image reading device according to claim 5, further comprising a light receiving amount adjusting means for adjusting the amount of light received by the photoelectric conversion element to a state where the amount of light received by the photoelectric conversion element disappears, It has a light source for illumination, and a photoelectric conversion element that receives transmitted light or reflected light from the illuminated original and outputs an image signal according to the received light, and converts the light image of the original into a light that corresponds to the brightness and darkness of the light. During pre-scanning, the level of the image signal at the brightest part within the trimming area of the document to be read is detected among the image signals output from the photoelectric conversion element, and photoelectric conversion is performed. A received light amount margin detection means for determining the received light amount margin of the element, and from the determined received light amount margin, adjusts the amount of light emitted by the light source to a state where there is no margin for the received light amount of the photoelectric conversion element in the brightest part of the document to be read during main scanning. The image reading device according to claim (6), characterized in that it is provided with a light projection amount adjusting means, is the image reading device according to claim (4), which separates the image signals into a plurality of color components and reads each image signal. The image reading device according to claim (7), further comprising: the received light amount margin detection means and the received light amount adjustment means for part or all of each color component; An image reading device that reads each image signal after color separation into a plurality of color components, characterized in that the image reading device comprises the received light amount margin detection means and the light emitted amount adjustment means for a part or all of each color component. The image reading device according to (8) is defined in claims (4) and (5).
, (6) or (7), in the main scan, an image signal level adjustment means for adjusting the level of the image signal output from the photoelectric conversion element by the amount adjusted so that the photoelectric conversion element has no margin in the amount of light received. It is characterized by having the following.

[Operation] In the image reading method of claim (1), for each document,
Before the main scan, perform a gray scan in advance to find the margin of light received by the photoelectric conversion element at the brightest part within the trimming area of the document to be read, and then increase the amount of light received by the photoelectric conversion element until there is no margin for the amount of light received at the brightest part. I try to do the main scan with it raised.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading method of claim (2), when color separation is performed, the light reception amount margin of the photoelectric conversion element at the brightest part within the trimming area of the original to be read is determined for part or all of each color component, and the The main scan is performed with the amount of light received by the photoelectric conversion element being increased until there is no margin for the amount of light received in bright areas.

Therefore, for some or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion of the color components, the ratio of each color component can be freely manipulated.

In the image reading method of claim (3), claim (1)
The second is (2) (here, in the main scan, the output J of the photoelectric conversion element is reduced by the amount that the amount of received light is increased).

Therefore, as the output is lowered, the noise signal also decreases.
It is possible to maintain an improved S/N ratio.

Furthermore, an image signal faithful to the original can be obtained.

In the image reading device of claim (4), the light source transmits or reflects the document to be read with a constant amount of light during pre-scanning and during main scanning. The photoelectric conversion element receives transmitted light or reflected light from the illuminated document, and outputs an image signal according to the amount of received light. The light image of the original is read as an electrical image signal corresponding to the brightness and darkness of the light. The received light amount margin detection means detects the level of the image signal of the brightest part within the trimming area of the document to be read among the image signals output from the photoelectric conversion element during pre-scanning, and detects the received light amount margin of the photoelectric conversion element. seek. The received light amount adjusting means adjusts the amount of received light during the main scan based on the obtained received light amount margin.
The amount of light received by the photoelectric conversion element is adjusted so that there is no margin for the amount of light received by the photoelectric conversion element in the brightest part of the document to be read.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading apparatus according to claim (5), the light source provides transmissive illumination or reflective illumination of the document to be read during pre-scanning and during main scanning.

The photoelectric conversion element receives transmitted light or reflected light from the illuminated document, and outputs an image signal according to the amount of received light. The light image of the original is read as an electrical image signal corresponding to the brightness and darkness of the light. The received light amount margin detection means detects among the image signals output from the photoelectric conversion element during pre-scanning.
The level of the image signal at the brightest part within the trimming area of the document to be read is detected, and the margin for the amount of light received by the photoelectric conversion element is determined.

The light projection amount adjusting means adjusts the light projection amount of the light source to a state where there is no light reception amount margin of the photoelectric conversion element in the brightest part of the document to be read during the main scan based on the determined light reception amount margin.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading device of claim (6), claim (4)
The apparatus reads each image signal after color separation into a plurality of color components, and includes the received light amount margin detection means and the received light amount adjustment means for part or all of each color component.

Therefore, for part or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion, the proportion of each color component can be freely manipulated.

The image reading device according to claim (7) is the image reading device according to claim (5), wherein each image signal is separated into a plurality of color components, and each image signal is read, and the received light amount margin detection means detects a part or all of each color component. and a light emitting amount adjusting means.

Therefore, for part or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion of the color components, the ratio of each color component can be freely manipulated.

In the image reading device of claim (8), claim (4)
, (5), (6), or (7), the image signal level adjusting means adjusts the image output from the photoelectric conversion element by the amount adjusted so that the photoelectric conversion element has no surplus in the amount of light received in the main scan. Adjust the signal level.

Therefore, the noise signal decreases by the amount that the output is decreased.
A state in which the S/N ratio is improved can be maintained.

Furthermore, an image signal faithful to the original can be obtained.

[Example] Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 shows a cylinder-type image reading device according to an embodiment of the present invention, and parts corresponding to those of a conventional image reading device are given the same reference numerals.

The second image reading device includes a transparent cylindrical cylinder 2 and a big asophor unit 4. A document 6 such as a film is wound on the cylinder 2. The pickup unit 4 includes a white light source 8, a photomultiplier 10 as a photoelectric conversion element, a reflection mirror 12, and a condenser lens 14.
, a pickup lens 16, a filter 18, and other optical system devices are provided.

The pink-up unit 4 is also provided with a received light amount margin detection means 32, an image signal level adjustment means 34, and a received light amount adjustment means 36.

The light source 8 is energized with constant voltage and current, and provides a constant amount of light. to project light. The light projected from the light source 8 is reflected by the reflecting mirror 12 and focused onto the original 6 by the condensing lens 14 . A portion of the light that has passed through the original 6 is taken into the pickup unit 4 by the pickup lens 16 and guided onto the photomultiple 10 via a filter 18 and other apertures and mirrors (not shown). Thereby, the photomultiplier 10 outputs an image signal corresponding to the brightness and darkness density of the corresponding position of the original 6.

A motor 20 rotates the cylinder 2 in the direction shown by an arrow 22. Further, at this time, the pickup unit 4 is moved in the direction of arrow 26 by the motor 24 driven in synchronization with the motor 20. Therefore, the original 6 wound around the cylinder 2 is scanned in a spiral manner, and an image signal for the entire original 6 is output from the photomultiplier 10.

In this image reading device, a document 6 is wound around a cylinder 2, and
The reading operation for obtaining image signals for the entire document 6 is performed twice: a prescan and a main scan. In addition, this image reading device can trim the document 6 shown in FIG. The image signal can be arbitrarily trimmed for all or part of the area (for example, a positive image).

At the time of pre-scanning or after pre-scanning, the received light amount margin detection means 32 is operated and the document 6 to be read is activated.
The highlight level of the brightest part within the trimming area is determined. That is, when the trimming area is a portion of the original 6 surrounded by the imaginary line 38 shown in FIG.
The highlight level V shown in (■) in the figure is detected. The highlight level soi is the output voltage of the photomultiplier 10 at the brightest part (see FIG. 3). Note that even if there is a part brighter than copy 0 in the document 6 outside the trimming area, this part is not determined to be the brightest part. This is because the area outside the trimming area is unnecessary and will be discarded. Next, the received light amount margin detection means 32 detects the received light jlV at the brightest part of the photomultiple 10. and specified maximum output voltage ■1. ! From this, the received light amount margin, that is, Imaxl, (see FIG. 3) is determined. Note that Iffi@X is the maximum amount of light that the photomultiplier 10 can receive when the transmittance of the brightest part of the original 6 is 100% within a range where clipping does not occur. Further, V i and a are the specified maximum output voltages output by the photomultiplier 10 in this case.

Moreover, ■ is the amount of light received by the photomultiplier 10 in the case of the output voltage ■7.

Once the received light amount margin is determined, the received light amount adjusting means 36 and the image signal level adjusting means 34 are operated for the main scan.

The received light amount adjusting means 36 adjusts the photomultiply 10 to a state where there is no margin for the received light amount of the photomultiplier 10 at the brightest part of the document 6 to be read during the main scan based on the obtained received light amount margin.
Adjust the amount of light received at 0. This amount of light received is Photomul 10
A state in which there is no margin for the amount of received light (1, , , -1, = O:
(see FIG. 3), that is, the maximum amount of received light is Ia,X, so that the specified maximum output voltage Vffi@t is output from the photomultiple 10 at the brightest part during the main scan.

On the other hand, the noise voltage (2) output from the photomultiplier 10 is constant. Therefore, during the main scan, even if the original is relatively dark at the highlight level, the amount of light received by the photomultiplier 10 is increased and the main scan is performed, so the ratio of image signals increases and the image signal to noise signal ratio ( The S/N ratio) becomes V m, , / V, and the S/N ratio improves.

In the main scan, the image signal level adjustment means 34
The level of the image signal output from the photomultiplier 10 is adjusted by the amount adjusted so that the photomultiplier 10 has no surplus in the amount of light received. In other words, the level of the image signal output from the photomultiplier 10 is V 1+1 @! is 1, /I
may be doubled (=V,/V,,,,). As a result, the image signal becomes smaller or the noise signal vN
It also doubles by 1,/I-, (-V,/V,,,), and the S/N ratio can be maintained in an improved state. As a result, it is possible to obtain an original image signal with a low highlight level for a document with a low highlight level.

FIG. 4 is a more specific configuration diagram of an image reading device according to an embodiment of the present invention, and parts corresponding to those of the conventional image reading device and the image reading device of FIG. 1 are given the same reference numerals. .

In this embodiment, the received light amount margin detection means 32 includes a received light amount margin detection circuit 42 and a CPU 44.

The received light amount margin detection circuit 42 includes a gate 46 and a peak holder 48. The image signal level adjustment means 34 includes a gain adjustment amplifier 50 and a CPU 44.

The received light amount adjusting means 36 includes a gradation filter 52 and a motor 54 for moving the gradation filter 52.
and the CPU 44.

The cladding filter 52 is arranged near the light source 8 so as to block the light irradiated from the light source 8 onto the original 6.

When the motor 54 is driven to rotate in accordance with a command from the CPU 44, the gradation filter 52 is moved and the original 6 is moved from the light source 8.
Continuously in the range of 0% to 100% of the amount of light irradiated to the
Or attenuated and adjusted in stages. by this,
The amount of light received by Photomano 1 and 0 is adjusted.

Transmittance K of gradation filter 52 (0≦to≦1
) is the standard transmittance K at the time of pre-scanning to find the margin for the amount of light received by Photomaru 10. fixedly adjusted to This standard transmittance K. is usually set to 5 to widen the adjustment range.
The transmittance is set between 0% and 60%. Note that the brightness I of the light source 8. , the gradation filter 52 has a standard transmittance K. When the brightest part of the document 6 is the highest possible, that is, when the transmittance is 100%, the photomultiplier 1
It is fixedly set so that the received light amount is 0 or the maximum received light amount ■□,y.

The received light amount margin detection circuit 42 determines the light level of the brightest part within the trimming area of the original 6 among the image signals output from the photomultiple 10 during pre-scanning. During pre-scanning, a reset signal is sent from the CPU 44 to the peak holder 48, and the peak holder 48
or will be reset. Also, during prescan, CPtJ4
4 sends a trimming signal to the gate 46 corresponding to the trimming region. Gate 46 sends the image signal from photomultiple 10 to peak holder 48 while receiving the trimming signal.

The peak holder 48 stores the maximum of the image signals, that is, the highlight level V□. therefore,
The light level within the trimming area of the document 6 is determined. CPL'44 takes in the highlight level and calculates the margin of the amount of light received by the photomultiplier 1O.

When the margin for the amount of light received by the photomultiply 10 is determined, the transmittance of the gradation filter 52 is adjusted to a value determined by, for example, so that the margin for the amount of light received by the photomultiply 10 is eliminated. At this time, it is not based on the amount of light received, but from Ia, X and
From this, the standard transmittance may be directly corrected to 0 to determine the transmittance K at which there is no margin for the amount of received light. Note that this transmittance varies depending on the original to be read. Further, even for the same document, the trimming area differs depending on the trimming area.

After completing the adjustment of the light receiver 9 of the photomultiplier 10 as described above, the main scan is then performed.

During the main scan, the CPU 44 uses the Kane adjustment amplifier 50.
A gain setting signal for freely setting the gain of is sent to the Kane adjustment amplifier 50. The gain adjustment amplifier 50 changes the level of the image signal output from the photomultiple 10 according to the gain setting signal.

Next, an image reading method will be explained.

In addition, the previous light source is I. , the brightness of the original 6, that is,
Transmittance or reflectance is T (0≦T≦1), Photomal 1
Let the output of 0 be ■, and the sensitivity of Photomul 10 be Q (Q=output voltage/amount of light received). Note that the light amount loss in the optical system is ignored, and 1. , Q is fixed in one variation.

The light iLJ transmitted through the gradation filter 52 is J
=K・1. (1). Therefore, the amount of light transmitted through the original 6, that is,
The amount of light received by the photomultiplier 10 is J-T.

As a result, the output voltage ■ of Photomul 10 is V=Q
-J-T (2) = -1 for Q-, -T (3).

Here, as mentioned above, the standard transmittance K. is the value at which the output of the photomultiplier 10 is V, 8, when the brightest part (T=1) that is considered to be the brightest part of the original 6 is read. Therefore, the light itJ transmitted through the gradation filter 52 at this time is the standard light amount J. Then, from (1), it becomes.

(2)■ ~“.1, J = J,.

Substitute T=1 and, \・may-Q becomes.

here, J 0% When you ask for Ko, becomes. Also, from equation (4), K. , JO are determined.

In conventional image reading devices, K, J or the standard value K.

This corresponds to a case where J is fixed and cannot be varied.

In the present invention, first, the motor 54 is rotationally driven by the CPU 44 to move the gradation filter 52, and the amount of light transmitted through the gradation filter 52 is set to a standard value. Therefore, the amount of light projected onto the original 6 is J=J,=1.
− becomes.

Next, the document 6 is prescanned in this state.

This is a scan before the main scan, and a scan with coarse resolution is sufficient. At the same time, the received light amount margin detection circuit 42 is operated to determine the maximum value V of the image signal within the trimming area of the document 6. (See Figure 3).

Next, calculate the adjustment rate using the following formula.

This adjustment rate A is a value indicating the relative brightness of the brightest part of the original 6 to be read with respect to the original with T=1. When A=1, the brightest part of this original 6 has a transmittance of 100%.

The transmittance at the brightest part decreases, and the value increases as the document becomes darker.

Next, move the gradation filter 52, and set the transmittance K of the gradation filter 52 to =A-,
(8). Also, the gain of the gain adjustment amplifier 50 is set to 1/A (1/A≦1)
.

Next, perform the main scan.

The effects of this image reading device and image reading method will be described in comparison with the conventional case.

In the conventional case, the image signal at the brightest part is equivalent to the actual scan with K = fixed and J = J0, so the image signal at the brightest part is
■Yes. At this time, the noise signal is v7. Therefore, the S/N ratio is V,/V.

It is.

In the case of the present invention, during the main scan, the transmittance of the gradation filter 52 is =A-K, and the amount of light projected onto the original 6, that is, the amount of light received by the photomultiplier 10, is increased by A times. Therefore, the output of the photomultiplier 10 is A times (i) o, that is, A·V, (=V, , ). At this time, the noise signal is the same <VN. By this, S
/N ratio becomes ■□, 1/■, =A-V□/v1. Therefore, the S/N ratio is improved by a factor of A.

Furthermore, since the gain adjustment amplifier 50 multiplies the noise signal by 1/A, the noise signal is finally VN with respect to the image signal Vm.
/ Becomes A.

Therefore, the S/N ratio is v,/(VN/A)=A・
V, /VN, and the S/N ratio is still A times (
A=V, , /V, ≧1) It can be seen that the improved S/N ratio can be maintained.

That is, according to the present invention, the S/N ratio of the image signal can be increased by A times. Furthermore, for a document with a dark highlight level, a correspondingly lower image signal will be obtained, making it possible to obtain an image signal that is faithful to the document.

By the way, the S/N ratio of the improved image signal can be calculated as follows.

This value is the S/N ratio unique to Photomul 10, and further improvement is physically impossible. In other words,
The present invention takes full advantage of Photomaru 10's cleanliness.

FIG. 5 shows an image reading device according to another embodiment of the present invention,
Parts corresponding to those in the embodiment of FIG. 4 are given the same reference numerals.

This image reading device is designed to read a color original 6, for example, red (R), gnome (G),
The image signal is separated into three components of blue (B) and read.

Color separation is performed by extracting R color component and B color component light from the light reflected by the reflection mirror 60 using tichroic mirrors 62 and 64, and reflecting the remaining G component light by the reflection mirror 66. . These R, B, and G color component lights are passed through an R color filter 18R, a B color filter 1.8 . , through the G color filter 18c, the photomultipliers 10R, 10, 1
Each light is received by 0o.

A gradation filter 52°52Y is installed near the light source 8.
, 52m is installed. In the cladding filter 52o, only the transmittance of R light changes, and the transmittances of B and G lights are constant values close to 1. The other gradation filters 52Y and 52M change only the transmittance of B light and G light, respectively. cladage filter 52c,
52Y, 52M are motors 54c, 54Y,
54M. Therefore, fo;
- The amount of light received by Maru 10R, Ion, and 10c can be adjusted independently. Also, Photomaru+OR, 10B,
For the output of 10c, received light amount margin detection circuits 42R, 42
H, 42c and Kane adjustment amplifier 50R, 50,, 5
0G or connected respectively.

The CPU 44 includes light receiving amount margin detection circuits 42R, 42B, 4
Highlight level of each color component from 2G ■R, vB,
Load v6□ and adjust each color component 1'A
Find RA,,A,.

The adjustment rate AR, A, , A6 can be found as follows. With these adjustment rates AR, As, and Ac, the gradation filter 52. , 52. , 52M to maximize the light reception of the photomultiplier IOR, 10B, and IOG.

Therefore, for all of each color component, Photomul 10
．． , 10. ．． The ratio of the image signal to the constant noise signal output from 106 increases, and the S/N ratio improves.

In addition, in the case of positive color originals, the gain of the gain adjustment amplifiers 50R, 508, 50 (, 1/AR1/
A c, 1/A a times. Therefore, the noise signal is reduced by the reduction in the output of the photomultiples 10R, 10, 10c, and an image signal faithful to the brightness of the original can be obtained while improving the S/N ratio.

Note that in the case of negative color originals, the gains of the gain adjustment amplifiers 50R, 50B, and 50a are set to 1, respectively.
” is left as is. That is, Photomaru 1o1. +1
The outputs of 0B and 106 are taken in as they are as image signals.

This is because the negative color is covered with an orange mask. For this reason, NECA color has a lower R than PON color.
, G, and B are much darker.

Furthermore, the balance between R, G, and H is also significantly off.

The brightest part of NECA Color corresponds to the darkest part of the subject. The darkest part of the subject has less R, G, and 13 lights, and is often well balanced.

Therefore, color balance can often be achieved by aligning each color signal at the brightest part of a negative color.

Therefore, by simply adjusting the gradation filters 52C, 52Y, and 52M at the adjustment rates AR, An, , Ac, the color balance of the negative color is automatically corrected. , 106 have a well-balanced color. However, for negative color, the gain adjustment amplifier 50
R, 50B, 50. The gain of 1/AR, 1/At
,.

If the image signal is multiplied by 1/AR, the balance of R, G, and B may become significantly out of balance in the image signal as in negative color. Therefore, the gain amount for gain adjustment is left at "1".

In the second case as well, for all color components, the ratio of the image signal to the constant noise signal output from the photomultiples 10R, 1011, and XOG increases, and the S/N ratio improves.

Note that the gradation filter 52, the motor 54, the received light amount margin detection circuit 42, and the gain adjustment amplifier 50 may be provided for only some of the R, G, and H color components. By performing this on a portion of the color components in this manner, the ratio of each color component can be freely manipulated.

FIG. 6 shows a cylinder-type image reading device according to another embodiment of the present invention, and parts corresponding to those in the embodiment of FIG. 1 are given the same reference numerals.

What should be noted in this embodiment is that a light projection adjustment means 70 is provided in place of the received light amount adjustment means 36, and the amount of light emitted from the light source 8 can be changed.

The light projection amount adjusting means 70 adjusts the light projection amount of the light source 8 so that there is no margin for the light reception amount of the photomultiple 10 at the brightest part of the original document 6 to be read during the main scan based on the obtained light reception amount margin.

The light emitting amount adjusting means 70 maintains a constant voltage ■ during pre-scanning. , powering the light source 8 with a current 10.

At the time of the main scan, the voltage Vo or the current 1° is adjusted so that the amount of light emitted is multiplied by A, and the power is energized.

Therefore, the amount of light received by the photomultiplex 10 can be changed as appropriate, and the S/N ratio of the output of the photomultiplex 10 can be improved.

FIG. 7 shows an image reading device according to another embodiment of the present invention, and parts corresponding to the embodiments of FIGS. 5 and 6 are given the same reference numerals.

What should be noted in this example is the R, G, and B color light sources 8R,
8B and 8G are used, and the light sources 8R, 8, 8G are independently powered by the light emitting amount adjusting means 70, and the light sources 8R, 8G are
8, 8, the amount of light projected can be changed.

Therefore, the amount of light received by the photomultiples 10R, 10, 10C changes independently and appropriately, and the photomultiples 10. , 10.
.

The S/N ratio of the output of 106 can be improved.

FIG. 8 shows a flat image reading device according to another embodiment of the present invention, and parts corresponding to those in the embodiments of FIGS. 4 and 6 are given the same reference numerals.

What should be noted in this embodiment is that a CCD line sensor 72 is used as the photoelectric conversion element instead of the photomultiplier.

A document 6 is placed on a transparent table 74. A light source 8 is provided above the table 74.

The light transmitted through the original 6 from the light source 8 forms an image of a linear portion of the original 6 on the COD line sensor 72 by the pickup lens 16 . The CCD line sensor 72 is provided with pixels arranged in a row, and each pixel outputs a signal corresponding to the density of a corresponding position on the document 6. The table 74 is moved in the direction of arrow 26 by the motor 24,
The above operation is performed for each main scanning line, and image signals for the entire document 6 are sequentially obtained.

Note that the CCD drive circuit 76 operates according to a command from the CPtJ 44 while keeping the accumulation time (that is, shutter time) of the CCD line sensor 72 constant.

The CCD line sensor 72 accumulates charges in each pixel according to the amount of received light according to this accumulation time (ie, shutter time), and sequentially outputs them to the amplifier 78.

The amplifier 78 converts the charge output from the CCD line sensor 72 into a voltage output and also performs impedance conversion. Note that the light source 8 may have non-uniformity in the amount of light. Furthermore, variations in sensitivity may occur in each pixel of the CCD line sensor 72. A shading correction circuit 80 is connected to the output of the gain adjustment amplifier 50 in order to uniformly correct this Mitsugake non-uniformity and variations in sensitivity of each pixel. Further, the shading correction circuit 80 may be provided at a position shown by the imaginary line behind the amplifier 78.

In this embodiment, during pre-scanning, the light receiving amount margin of the CCD line sensor 72 can be accurately determined without passing through the shading correction circuit 80.

Therefore, during the main scan, the CCD line sensor 7
The amount of light received by each pixel of 2 does not exceed the maximum amount of light received I8, and an excessive amount of light received can be avoided.

When provided at the position shown by the virtual line, the image signal read into the received light amount margin detection circuit 42 during pre-scanning is corrected by the shading correction circuit 80 to uniformly correct uneven light amount and variations in sensitivity of each pixel. There is. Therefore, the received light amount margin can be determined using an image signal that is faithful to the original 6, and reading unevenness does not occur.

In the second embodiment, the amount of light emitted from the light source 8 during pre-scanning and during main scanning is changed by the light emitting amount adjustment means 70 to perform CC control.
Although the amount of light received by the D line sensor 72 is changed, the following method may be used. The amount of light emitted by the light source 8 is made constant during pre-scanning and during main scanning. And CPL14
4, a command is issued to the CCD drive circuit 76 so that the CCD drive circuit 76 changes the accumulation time or shutter time of the CCD line sensor 72 during pre-scanning and main scanning.

With this, it is possible to change the amount of light received by the CCD line sensor 72. Furthermore, although not shown, the amount of light received by the CCD line sensor 72 may be changed using a gradation filter 52. Alternatively, the present invention may be implemented by using one or more CCD line sensors to receive color-separated light so as to be able to handle color originals.

Figure 10 shows the 11th line using three CCD line sensors.
The figure shows an example of a case in which one CCD line sensor is used to support color.

The numbers given in the figures here refer to Figures 5, 7,
The one used in Figure 8 etc. is used.

In addition, in FIG. 11, the light projection amount adjusting means 70 is the light source 8.
8.8B and 8G each sequentially (only one at a time)
The amount of light emitted is adjusted while the light is turned on, which allows the single CCD line sensor 72 to sequentially read the R.
, B, and G can be maximized.

In the above-described embodiment, the received light amount margin detection means 32 is configured by the received light amount margin detection circuit 42 and the CPU 44, but it may be configured by other components, for example, the frame memory 56 and the CPU 44 as shown in FIG. It may be configured.

Image signals are sequentially stored in the frame memory 56.

The CPU 44 outputs an address signal to the frame memory 56 corresponding to the trimming area, and takes in an image signal from the frame memory 56. Then, the levels of the captured image signals are compared to determine the highlight level. In this way, the highlight level can also be detected using the frame memory 56.

In addition, gradation filters 52.52. , 52Y.

52M is arranged near the light source 8, but it may be arranged anywhere between the light source 8 and the original 6 or between the original 6 and the photomultiply 10.

[Effect of the invention] In the image reading method of claim (1), for each document,
Before the main scan, perform a pre-scan in advance to determine the amount of light received by the photoelectric conversion element at the brightest part within the trimming area of the document to be read, and then increase the amount of light received by the photoelectric conversion element until there is no margin for the amount of light received at the brightest part. I try to do the main scan with it raised.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading method of claim (2), when color separation is performed, the light reception amount margin of the photoelectric conversion element at the brightest part within the trimming area of the original to be read is determined for part or all of each color component, and the The main scan is performed in a state where the amount of light received by the photoelectric conversion element is increased until there is no margin for the amount of light received in the bright area.

Therefore, for part or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion of the color components, the ratio of each color component can be freely manipulated.

In the image reading method of claim (3), claim (1)
Or in (2), in the main scan, the output of the photoelectric conversion element is reduced by the amount of increased received light amount.

Therefore, the noise signal is reduced by the amount that the a power is reduced.
It is possible to obtain an image signal faithful to the brightness of the original while improving the S/N ratio.

In the image reading device of claim (4), the light source transmits or reflects the document to be read with a constant amount of light during pre-scanning and during main scanning. The photoelectric conversion element receives transmitted light or reflected light from the illuminated document, and outputs an image signal according to the amount of received light. The light image of the original is read as an electrical image signal corresponding to the brightness and darkness of the light. The received light amount margin detection means detects the level of the image signal of the brightest part within the trimming area of the document to be read among the image signals output from the photoelectric conversion element during pre-scanning, and detects the received light amount margin of the photoelectric conversion element. seek. The received light amount adjusting means adjusts the amount of received light during the main scan based on the obtained received light amount margin.
The amount of light received by the photoelectric conversion element is adjusted so that there is no margin for the amount of light received by the photoelectric conversion element at the brightest part of the document to be read.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading apparatus according to claim (5), the light source provides transmissive illumination or reflective illumination of the document to be read during pre-scanning and during main scanning.

The photoelectric conversion element receives transmitted light or reflected light from the illuminated document, and outputs an image signal according to the amount of received light. The light image of the original is read as an electrical image signal corresponding to the brightness and darkness of the light. The received light amount margin detection means detects among the image signals output from the photoelectric conversion element during pre-scanning.
The level of the image signal at the brightest part within the trimming area of the document to be read is detected, and the margin for the amount of light received by the photoelectric conversion element is determined.

The light projection amount adjusting means adjusts the light projection amount of the light source to a state where there is no light reception amount margin of the photoelectric conversion element at the brightest part of the document to be read during main scanning based on the determined light reception amount margin.

Therefore, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves.

In the image reading device of claim (6), claim (4)
An image reading device that separates each image signal into multiple color components and reads each image signal, and for some or all of each color component,
The apparatus includes the received light amount margin detection means and the received light amount adjustment means.

Therefore, for part or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion of the color components, the ratio of each color component can be freely manipulated.

The image reading device according to claim (7) is the image reading device according to claim (5), which reads each image signal after color separation into a plurality of color components, and for a part or all of each color component,
The apparatus includes the received light amount margin detection means and the light emitted amount adjustment means.

Therefore, for some or all of each color component, the ratio of the image signal to the constant noise signal output from the photoelectric conversion element increases, and the S/N ratio improves. Furthermore, by performing this on a portion, the proportion of each color component can be freely manipulated.

In the image reading device of claim (8), claim (4)
, (5), (6), or (7), the image signal level adjusting means adjusts the image output from the photoelectric conversion element by the amount adjusted so that the photoelectric conversion element has no surplus in the amount of light received in the main scan. Adjust the signal level.

Therefore, as the output is lowered, the noise signal also decreases.
It is possible to obtain an image signal faithful to the brightness of the original while improving the S/N ratio.

[Brief explanation of drawings]

FIG. 1 shows a cylinder-type image reading device according to an embodiment of the present invention.
FIG. 2 is a diagram showing the original 6, FIG. 3 is a diagram for explaining the S/N ratio improvement operation in the input/output characteristics of the photomultiplier 10, and FIG. 4 is a diagram showing a specific example of an embodiment of the present invention. Configuration diagram, FIG. 5 is an image reading device according to another embodiment of the present invention, FIG. 6 is an image reading device according to another embodiment of the present invention, and FIG. 7 is an image reading device according to another embodiment of the present invention. , FIG. 8 shows a planar image reading device according to another embodiment of the present invention, and FIG. 9 shows a received light amount margin detection means 3.
FIGS. 1O and 11 show other embodiments of the image reading apparatus of the present invention, and FIG. 12 shows a conventional cylinder type image reading apparatus. 6... Original 8... Light source 10... Photomultiple 32... Received light amount margin detection means 34... Image signal level adjustment means 36--Received light amount adjustment means 70--Emitted light amount adjustment means 72- ... CCD line sensor 5th diagram Figure 1, Lax O Received light amount diagram Figure 1 Image signal diagram UR Figure 11

Claims (8)

[Claims] (1) For each document, pre-scan before the main scan to determine the amount of light received by the photoelectric conversion element at the brightest part within the trimming area of the document to be read, until there is no margin for the amount of light received at the brightest part. An image reading method characterized by performing main scanning while increasing the amount of light received by a photoelectric conversion element. (2) When performing color separation, perform a pre-scan before the main scan to determine the amount of light received by the photoelectric conversion element at the brightest part within the trimming area of the document to be read for some or all of each color component. . An image reading method characterized in that main scanning is performed in a state where the amount of light received by a photoelectric conversion element is increased until there is no margin for the amount of light received at the brightest part. (3) The image reading method according to claim (1) or (2), characterized in that in the main scan, the output of the photoelectric conversion element is reduced by an amount corresponding to the increase in the amount of received light. (4) A light source that illuminates the original to be scanned with a constant amount of light during pre-scanning and main scanning, and an image signal that receives the transmitted or reflected light from the illuminated original and generates an image signal according to the amount of received light. An image reading device that has a photoelectric conversion element that outputs a photoelectric conversion element and reads an optical image of a document as an electric image signal corresponding to the brightness and darkness of the light. , a received light amount margin detection means that detects the level of the image signal of the brightest part within the trimming area of the original to be read, and determines the received light amount margin of the photoelectric conversion element; 1. An image reading apparatus comprising: a light receiving amount adjusting means for adjusting the amount of light received by the photoelectric conversion element so that there is no margin for the amount of light received by the photoelectric conversion element in the brightest part of the image reading apparatus. (5) A light source that transmits or reflects the illumination of the document to be read during pre-scanning and main scanning, and a photoelectric device that receives transmitted or reflected light from the illuminated document and outputs an image signal according to the amount of received light. An image reading device that includes a conversion element and reads an optical image of an original as an electric image signal corresponding to the brightness and darkness of the light, and the image reading device reads the original image to be read from among the image signals output from the photoelectric conversion element during prescanning. A received light amount margin detection means that detects the level of the image signal at the brightest part within the trimming area of the photoelectric conversion element and determines the received light amount margin of the photoelectric conversion element; An image reading device comprising: a light projection amount adjusting means for adjusting the light projection amount of the light source to a state where there is no margin for the amount of light received by the photoelectric conversion element. (6) An image reading device that separates each image signal into a plurality of color components and reads each image signal, comprising the above-mentioned received light amount margin detection means and received light amount adjustment means for some or all of each color component. The image reading device according to claim (4). (7) An image reading device that separates each image signal into a plurality of color components and reads each image signal, characterized by comprising the above-mentioned received light amount margin detection means and light emitted amount adjustment means for some or all of each color component. The image reading device according to claim (5). (8) In the main scan, the image signal level adjusting means is provided for adjusting the level of the image signal output from the photoelectric conversion element by the amount adjusted so that the amount of light received by the photoelectric conversion element is eliminated. (4), (5), (6
) or the image reading device of (7).