JP3112325B2 - Image input method and apparatus - 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 input method and apparatus using a solid-state image pickup device such as a CCD.

[0002]

2. Description of the Related Art Conventionally, a solid-state imaging device such as a CCD is often used to read an image of a document and convert the image into an electric signal (output signal).

FIG. 7 is a diagram showing the relationship between the incident light intensity of the CCD and the output signal level. The output signal level of the CCD is almost proportional to the intensity of the incident light when the accumulation time is constant, but there is a limit above and below it.

That is, when the image is read by the CCD, when the intensity of the incident light is excessive (too bright), the output signal is saturated, and when the intensity is too small (too dark), Due to the presence of dark current in the CCD, the S / N ratio is reduced or the output signal is not guaranteed. Therefore, as the intensity of the incident light, a portion having an intermediate linear characteristic (allowable range of the intensity of the incident light) IL to IH is used.

Therefore, for example, when an original image is input, the average density of the original image is detected, and the luminance (light amount) of the illumination light source is controlled in accordance with the average density of the incident light.
A method of improving the S / N ratio by setting the position near the center of the linear characteristic of the CD is often used.

[0006]

However, even when such a method is used, if the density difference (contrast) of the original image is large, the original image is out of the allowable range.
As a result, there is a problem that an image of a light portion (bright portion) becomes unclear and an SN ratio of a dark portion (dark portion) is reduced.

[0007] Also, the luminance (light amount) due to the deterioration of the light source, etc.
Even when the value of has decreased, the allowable range may be exceeded and the same problem may occur. To cope with such a problem, an apparatus described in Japanese Patent Application Laid-Open No. 60-180279 detects the luminance level of a light source, and changes the accumulation time for each line of a document image based on the detected value. ing. By changing the accumulation time, the allowable range of the luminance of the light source can be changed, so that a clear image can be obtained even when the luminance is reduced.

However, according to this method, when the difference in gray level of an image within one line is large, the same problem occurs outside the allowable range. The present invention has been made in view of the above problems, and has as its object to obtain a wide dynamic range so that an output signal of an image sensor is not saturated and an S / N ratio is not reduced even when an image has a large difference in shading.

[0009]

According to the first aspect of the present invention, there is provided a method for solving the above-mentioned problems, wherein an electric signal is stored on the basis of the intensity of light incident on each pixel and the amount of charge accumulated according to time. using an image pickup device which outputs a, a read image as an image input method for inputting image information by the image pickup device, by the imaging device, for the same pixel, a plurality of times with different storage times Performs reading, and enters for each pixel among a plurality of read image information.
Read at an appropriate accumulation time based on the specific intensity of light
Selected image information, and the image information selected for each pixel
For level differences due to differences in storage time
To be corrected .

According to a second aspect of the present invention, there is provided an image pickup device which outputs an electric signal based on the amount of electric charge accumulated according to the intensity and time of light incident on each pixel, and a device for the same pixel.
And the accumulation time setting means for variably setting the accumulation time in the imaging device, a memory for storing at least a portion of the image information read by the image sensor, the particular intensity of the incident light Each pixel as a reference
The selection signal outputting means for outputting a selection signal for selecting one of the image information, based on the selection signal,
Selection means for selecting and outputting, for each pixel, a plurality of pieces of image information read by the image sensor at different accumulation times, and correction means for correcting the image information so as to eliminate a difference in level due to a difference in accumulation time And is configured.

[0011]

The principle of the input method according to the present invention will be described with reference to FIG. 1 showing the principle of the present invention in the case of performing two readings and synthesizing with a standard accumulation time and twice the standard accumulation time. Will be explained.

In FIG. 1, the horizontal axis represents the intensity of the incident light (brightness of the original image) and the vertical axis represents the magnitude of the output signal of the CCD 11. Curve CL1 has a standard accumulation time t
When a is assumed, the accumulation time 2t is twice as long as the standard.
a represents each case.

In the curve CL1, the incident light intensity is IL1 to IH.
1 has a linear characteristic, and the output signal level at that time is VL to VH. In the curve CL2, the incident light intensity has a linear characteristic in the range of IL2 to IH2, and the output signal level at that time is VL to VH.

As is apparent from FIG. 1, IL2 <IL1,
IH2 <IH1. In other words, a portion having a high incident light intensity (portion IH2 to IH1) uses the curve CL1, and a portion having a low incident light intensity (portion IL2 to IH2) uses the curve CL2.
Is used, the dynamic range of the incident light intensity is widened.

Therefore, the portions IH2 to IH1 are read by the standard accumulation time ta,
Only those whose output signals exceed the reference voltage Vref are used by doubling them, and for the portions IL2 to IH2,
By reading with an accumulation time 2ta twice as long as the standard and combining them, the incident light intensity can be reduced to IL2 to IH1.
In contrast, a curve CLS1 having characteristics having linearity over a wide range in which the output signal level is VL to 2 · VH can be obtained.

In the synthesis, the standard storage time ta
Is doubled, but the part read by the standard accumulation time ta is left as it is,
The part read by the double accumulation time 2ta is halved
May be multiplied.

FIG. 2 shows a case where the reading is performed three times and the image is synthesized with the standard accumulation time ta, the standard accumulation time 2ta, and the standard accumulation time 4ta.

That is, the portion IH2 to IH1 is read using the standard storage time ta and quadrupled and used, and the portion IH3 to IH2 is read using the standard storage time 2ta and doubled. Used, IL3 ~
For the portion of IH3, the one read with an accumulation time four times as long as the standard is used, and by combining these, the output signal level becomes VL-4.multidot.VH with respect to IL3-IH1. A curve CLS2 having characteristics having linearity over the range can be obtained.

[0019]

3 is a block diagram showing a circuit of the image input device 1 according to the present invention, FIG. 4 is a diagram showing a connection state of the selector 15, and FIG. 5 is a timing chart showing signal states of various parts of the image input device 1. It is a chart.

The image input device 1 includes a CCD 11, an AD converter 12, a FIFO memory 13, a comparator 14, and a selector 1.
5, clock oscillator 16, and timing signal generator 1
7.

The CCD 11 outputs an output signal AD1 which is an analog signal based on the amount of charge accumulated according to the intensity and time of light incident on each pixel. That is, the output signal AD1 is a signal having a voltage value corresponding to the brightness of the portion corresponding to each pixel and the accumulation time ta when the image of the document is read. Output signal AD
1 is output for each pixel in synchronization with the clock signal CLK output from the timing signal generator 17.

The accumulation time ta of the CCD 11 is determined by the interval of the timing signal S1 output from the timing signal generator 17. Note that each line of the document image is read twice, and the first time is read with twice the standard accumulation time 2ta and the second time is read with the standard accumulation time ta.

The AD converter 12 quantizes the output signal AD1 from the CCD 11 and converts it into image data DD1 which is a digital signal. The FIFO memory 13 stores the image data DD1 for one line in synchronization with the clock signal S2 output from the timing signal generator 17, and sequentially writes the image data DD1 read for the first time for each line. In the second reading of the same line, the previously written image data DD1 is sequentially read and output as image data DD2.

The comparator 14 is a selection signal output means in the present invention, and outputs the image data D output from the AD converter 12.
D1 is compared with the reference data Dref for each pixel, and when the image data DD1 is larger than the reference data Dref, the selection signal S4 is output.

The reference data Dref is a value of the image data DD1 corresponding to a specific intensity of the light incident on the CCD 11, and in this embodiment, the upper limit of the incident light intensity when reading with a storage time 2ta which is twice the standard. It is a digital value of the reference voltage Vref corresponding to IH2.

The selector 15 is a selection means in the present invention, and includes the image data DD1 output from the AD converter 12 and the image data DD2 read from the FIFO memory 13.
One of the data is selected for each pixel based on the selection signal S4 and output as image data DD3.

That is, when the selection signal S4 is on, the image data DD1 is turned off, and when the selection signal S4 is off, the image data DD2 is turned off.
Are selected and output. At this time, the selector 1
5, when the image data DD1 is selected, the value of the image data DD1 is doubled and output. That is, as shown in FIG. 4, each bit of the image data DD1 from the AD converter 12 is connected to the input bits B1 to Bn of the selector 15, and the least significant input bit B0 is always “0”. Image data D
A value obtained by doubling D1 is output as image data DD3. Therefore, the selector 15 is also a correction unit in the present invention.

Thus, level adjustment (correction) is performed between the image data DD1 read during the standard storage time ta and the image data DD2 read during the double storage time 2ta.

The clock oscillator 16 generates a clock signal serving as a source for controlling the overall timing, and the timing signal generator 17 selects the above-described timing signals S1 and S2 based on the clock signal. A signal S4 and a clock signal S3 for synchronization when the image data DD3 is taken in by an external device are generated and output. The timing signal generator 17 is an accumulation time setting means in the present invention.

Therefore, according to the image input apparatus 1, a curve CL2 is used for a portion smaller than the incident light intensity IH2 in FIG. 1, and a curve CL1 is used for a portion larger than the boundary, and the curve CL1 is used. The output signal AD1 at this time is doubled, and the curve CLS1 is eventually used.

Thus, even in the case where the contrast of the image is large and the width of the incident light intensity is wide, a wide dynamic range is used so that the output signal AD1 of the CCD 11 used as image data is not saturated and the SN ratio is not reduced. You can get a range.

FIG. 6 is a block diagram showing a circuit of an image input device 1a according to another embodiment of the present invention. 6, portions having the same functions as those of the image input device 1 of FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

The image input device 1a includes a CCD 11, an AD converter 12, a limiter 21, a FIFO memory 22, a FIFO
O memory 23, comparator 24, switch 25, selector 2
6, a multiplier 27, a clock oscillator 16, and a timing signal generator 17.

The limiter 21 controls the upper limit V of the output signal level.
The value of the image data DD1 exceeding H is set to “0”. However, when the signal S5 indicating that the accumulation time ta is standard is input from the timing signal generator 17, the image data DD1 is passed through as it is.

The FIFO memory 22 stores the image data DD7 for one line, and the FIFO memory 2
3 is the image data DD stored in the FIFO memory 22
7 stores a correction magnification SD7 corresponding to the accumulation time.

The comparator 24 compares the image data DD5 output from the limiter 21 with the image data DD6 read from the FIFO memory 22, and when the image data DD5 is larger (when the number of significant digits is larger). Select signal S4
Is output.

The switch 25 normally outputs the input selection signal S4 as it is as the selection signal S6. However, when the signal S5 is input, the switch 25 selects the ON state regardless of the state of the selection signal S4. The signal S6 is output.

The selector 26 selects one of the image data DD5 from the limiter 21 and the image data DD6 read from the FIFO memory 22 for each pixel on the basis of the selection signal S6, and selects an image. Data DD
7 is output. That is, when the selection signal S6 is on, the image data DD5 is output, and when the selection signal S6 is off, the image data DD5 is output.
D6 is selected and output. As a result, the larger one of the image data DD5 and the image data DD6 is output as the image data DD7.

Along with this, the magnification SD5 or FIF for correction output from the timing signal generator 17 is used.
One of the correction magnifications SD6 read from the O memory 23 is selected by the selector 26, and is output as the magnification SD7.

The multiplier 27 multiplies the image data DD7 output from the selector 26 by a magnification SD7 for correction and outputs the result as image data DD8. Next, the operation of the image input apparatus 1a will be described with reference to FIGS.

The first reading of one line of the original image is performed with a storage time 4ta which is four times the standard. C
The output signal AD1 from the CD 11 is converted into a digital signal by the AD converter 12, and is stored in the FIFO memory 22 as image data DD6 via the limiter 21 and the selector 26. At this time, the magnification “1” from the timing signal generator 17 is stored in the FIFO memory 23 for all the pixels.

The second reading of the original image is performed according to the standard 2
This is performed by the double accumulation time 2ta. The image data DD5 from the limiter 21 is supplied to the
The image data DD6 read from the O memory 22 is compared with the image data DD6, and the larger image data is output as the image data DD6, which is stored in the FIFO memory 22. As a result, the curve CL3 is used for a portion smaller than the incident light intensity IH3 of FIG. 2 and the curve CL2 is used for a portion larger than the boundary. Further, a magnification SD6 corresponding to the image data DD6 stored in the FIFO memory 22 is stored in the FIFO memory 23. In addition,
The magnification SD5 from the timing signal generator 17 at this time is
Is “2”.

The third reading of the original image is performed during the standard accumulation time ta. Similarly to the second time, the larger one of the image data DD5 from the limiter 21 and the image data DD6 read from the FIFO memory 22 is output from the selector 26. This allows
A curve CL1 is used for a portion larger than the boundary of the incident light intensity IH2 in FIG. At this time, the magnification SD5 from the timing signal generator 17 is “4”.

The image data D output from the selector 26
D6 is multiplied by a predetermined magnification for each pixel by the multiplier 27, and output as image data DD8 together with the clock signal S3.

According to the above-described embodiment, even if the intensity of the light incident on the CCD 11 covers a wide range due to the large difference in the density of the image, a wide dynamic range corresponding to the wide range can be obtained and used as image data. CC
A high resolution can be obtained without saturating the output signal of D11 and preventing a decrease in the S / N ratio in a dark part. Therefore, for example, when a color image is read, its color reproducibility can be improved.

In the above-described embodiment, the image data of the bright portion is doubled or quadrupled.
Although the number of significant digits in the dark portion increases, the number of significant digits in the bright portion does not increase. However, even if the resolution of the bright portion is low, no practical problem occurs.

In the above embodiment, the image input devices 1 and
The configuration of 1a can be various other than those described above. The CCD 11 can be applied to one-dimensionally or two-dimensionally arranged CCDs, and can also be applied to an image sensor other than the CCD.

[0048]

According to the present invention, a wide dynamic range can be obtained so that the output signal of the image sensor does not saturate and the S / N ratio does not decrease even in the case where the contrast of the image is large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is a block diagram showing a circuit of the image input device according to the present invention.

FIG. 4 is a diagram illustrating a connection state of a selector.

FIG. 5 is a timing chart showing a state of a signal of each unit of the image input device.

FIG. 6 is a block diagram showing a circuit of an image input device according to another embodiment of the present invention.

FIG. 7 is a diagram showing the relationship between the intensity of incident light of a CCD and the output signal level.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image input device 11 CCD (imaging device) 13, 22 FIFO memory (memory) 14, 24 Comparator (selection signal output means) 15 Selector (selection means, correction means) 17 Timing signal generator (accumulation time setting means) 26 Selector (selection means) 27 Multiplier (correction means)

Continuation of the front page (72) Inventor Eiichi Yoshida 2-3-3 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-61-158279 (JP, A) JP-A-63-109583 (JP, A) JP-A-3-42976 (JP, A)

Claims (2)

(57) [Claims] An image pickup device for outputting an electric signal based on the amount of electric charge accumulated in accordance with the intensity and time of light incident on each pixel, and reads an image with the image pickup device to input image information. An image input method according to any one of claims 1 to 3, wherein the same pixel is read a plurality of times with different accumulation times by the image pickup device, and a plurality of pieces of read image information are input to each pixel.
Reading at an appropriate accumulation time based on the specific light intensity
The selected image information is selected, and the image information selected for each pixel is compared with the accumulation time.
An image input method, wherein a correction is made so as to eliminate a difference in level due to a difference . 2. An image pickup device that outputs an electric signal based on the amount of electric charge accumulated according to the intensity and time of light incident on each pixel, and the accumulation time in the image pickup device is variable for the same pixel. Storage time setting means for setting; a memory for storing at least a part of the image information read by the image sensor; and a specific intensity of incident light as a reference . A selection signal output unit that outputs a selection signal for selecting one of the plurality of image information, based on the selection signal, a plurality of pieces of image information read by the image sensor at different accumulation times from each other, and output. An image input apparatus comprising: a selection unit; and a correction unit that corrects the image information so as to eliminate a difference in level due to a difference in accumulation time.