JPH099007A - Scanner - Google Patents

Abstract

PURPOSE: To provide a scanner which eliminates the difference of light receiving quantity for respective lines by means of the luminance fluctuation of a high frequency lighting fluorescent tube without depending on the period of a line read cycle and without depending on the shutter value of an electronic shutter. CONSTITUTION: A timing generator 60 generates the clock of an invertor frequency fINV and a second frequency-dividing circuit 66 frequency-divides the clock so as to generate the fetching signal (the LD signal of a frequency fLD) of one line. The clock of the invertor frequency fINV is added to an invertor 11 and the high frequency lighting of the fluorescent tube 10 is controlled. On the other hand, the LS signal is added to a CCD driving circuit 15 and the exposure timing of a CCD line sensor 14 is controlled. Thus, the period of the luminance fluctuation of the fluorescent tube 10 owing to high frequency lighting is completely synchronized with exposure timing when the CCD line sensor 14 accumulates charges by setting the lighting frequency fINV to be the multiple of a natural number of the fetching frequency fLD of one line. Thus, the irregularity of light receiving quantity for the respective lines, which the CCD line sensor 14 receives, can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanner, and more particularly, to high-frequency lighting control of a fluorescent tube of a scanner configured to use a fluorescent tube as illumination and to capture an image by a line sensor.

[0002]

2. Description of the Related Art As a scanner for reading an image or the like using a line sensor, for example, a film scanner has been proposed in which a developed still photo film is conveyed at a constant speed and the image of the film is read by the line sensor. (Japanese Patent Application Laid-Open No. 63-39267, Japanese Patent Application No.
-See the specification of No. 72079).

Not only this type of film scanner but also a scanner using a line sensor generally uses a fluorescent tube as a light source of its illumination system. However, as the reading speed increases, flicker occurs when the commercial frequency of 50 Hz or 60 Hz is lit, so that the fluorescent tube that is normally lit at high frequency (for example, 30 kHz) is generally used.

FIG. 5 is a graph showing the relationship between the conventional fluorescent tube surface brightness and the line sensor uptake cycle (line cycle: LD). FIG. 5A shows the high frequency lighting fluorescent tube current.
(B) shows the relationship between the fluorescent tube surface brightness corresponding to the tube current and the line period. Since the phosphor has an afterglow characteristic as shown in FIG. 3B, the surface brightness of the fluorescent tube does not completely become 0 as shown by the dotted line even when the tube current becomes 0, and is shown by the solid line. Such a change in brightness occurs in a cycle with a short duration.

High-frequency lighting period T _INV of such a fluorescent tube
On the other hand, the conventional line cycle T _LD is controlled irrespectively.
In the case of (1) and the section (2), the amount of light received by the line sensor is
(1)> (2), and strictly speaking, the received light amount of the line sensor is uneven. Nevertheless, in the conventional case, the reading speed is relatively slow, and the line sensor capture period T _LD is sufficiently longer than the lighting frequency T _{IN V} of the fluorescent tube (about 100 times).
Therefore, the difference in the amount of received light between section (1) and section (2) was so small that it could be ignored, and unevenness in the amount of received light for each line was not a problem.

[0006]

However, in the conventional scanner, the L-scanning speed is increased to cope with the further increase in the reading speed.
When the D period becomes short, or when the light amount is sufficient and the electronic shutter is extremely narrowed down, there is a problem that the unevenness of the received light amount for each line cannot be ignored. When unevenness occurs in the amount of light received for each line as described above, there arises a problem that an accurate image cannot be reproduced, such as a light and shade appearing on the screen.

For example, a fluorescent tube lighting frequency of 30 kHz, L
If the electronic shutter is narrowed down to 10% at a D cycle of 600 Hz, the difference in light amount between lines becomes on the order of several%, and a noticeable deterioration in image quality is recognized. The present invention has been made in view of such circumstances, and does not depend on the size of the line cycle, or on the shutter value of the electronic shutter,
An object of the present invention is to provide a scanner capable of eliminating the difference in the amount of received light for each line due to blinking of a fluorescent tube.

[0008]

In order to achieve the above-mentioned object, the present invention has a fluorescent tube for illumination turned on at a high frequency, and image light obtained by illuminating with the fluorescent tube is received by each light receiving portion of a line sensor. However, in a scanner that periodically adds a capture signal of one line and outputs the charge accumulated in each light receiving unit as an image signal, a lighting frequency for turning on the fluorescent tube at a high frequency is set to a capture frequency of the capture signal of one line. It is characterized in that it is a natural multiple of the frequency.

[0009]

According to the present invention, the lighting frequency for lighting the fluorescent tube for illumination at a high frequency is set to be a natural multiple of the capturing frequency of one line of the line sensor, so that the surface brightness of the fluorescent tube caused by the high frequency lighting is reduced. The change cycle and the exposure timing at which the line sensor accumulates the signal charge are perfectly synchronized. Fluctuation of the fluorescent tube surface brightness, that is, means the fluctuation of the image light illuminated by the light source, the period of the fluctuation of the image light due to the nature of the fluorescent tube and the signal accumulation timing of the line sensor By synchronizing, the influence of the fluctuation of the light source light can be eliminated from the light amount of each line received by the line sensor, regardless of the size of the capturing period of one line. That is, it is possible to eliminate unevenness in the amount of received light for each line due to fluctuations in the brightness of the fluorescent tube surface.

Further, the line sensor is provided with a so-called electronic shutter function of discharging unnecessary electric charges accumulated in each light receiving portion when a shutter gate pulse is inputted, and the shutter gate pulse is supplied to the signal for taking in one line. Even in a line sensor capable of controlling the exposure time of the light receiving section by controlling the timing at which it is generated, regardless of the frequency of the shutter gate pulse, the exposure start timing of the light receiving section for each line and the fluorescent tube Since it is synchronized with the lighting cycle of, the difference in the amount of received light for each line can be eliminated in the same manner as above. Therefore, regardless of the shutter value of the electronic shutter, it is possible to prevent the occurrence of the difference in the amount of received light for each line due to the brightness variation of the fluorescent tube.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a scanner according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of a film scanner to which the present invention is applied. This film scanner mainly includes a fluorescent tube 10 for illumination, an inverter 11, a photographing lens 12, and a CC.
D line sensor 14, analog amplifier 16, A / D converter 18, digital signal processing circuit 20, motor 31,
A film drive device including a capstan 32 and a pinch roller 33, a central processing unit (CPU) 40, and the like are provided.

The fluorescent tube 10 is connected to an inverter 11 and is controlled by the inverter 11 to perform high-frequency lighting. The developed negative film 52 pulled out from the film cartridge 50 is provided with an infrared cut filter (not shown). Illuminate through. The transmitted light transmitted through the film 52 passes through the taking lens 12 and the CCD line sensor 14
Is formed on the light receiving surface of

The inverter 11 is composed of one whose oscillation frequency can be controlled by a clock input from the outside, and is driven by a clock of an inverter frequency f _INV generated by the timing generator 60. The CCD line sensor 14 is provided with a light receiving portion for 1024 pixels in a direction orthogonal to the film transport direction, and the image light formed on the light receiving surface of the CCD line sensor 14 is R, G, B filters. Electric charges are provided and accumulated in each light receiving portion, and converted into R, G, and B signal charges in an amount according to the intensity of light. The R, G, and B charges thus accumulated are transferred to the shift register when a read gate pulse of one line period applied from the CCD drive circuit 15 is applied, and then sequentially converted into voltage signals by register transfer pulses. Is output.

Further, the CCD line sensor 14 is provided with a shutter gate and a shutter drain adjacent to each light receiving portion. By driving the shutter gate with a shutter gate pulse, the electric charge accumulated in the light receiving portion is charged. Can be swept out to the shutter drain. That is, this CCD line sensor 14
It is possible to control the electric charge accumulated in the light receiving unit according to the shutter gate pulse applied from the D drive circuit 15.
It has a so-called electronic shutter function.

The timing generator 60 includes an oscillator 6
2, a first frequency divider circuit 64, and a second frequency divider circuit 66. The original oscillation of the oscillator 62 is frequency- _{divided by} the first frequency divider circuit 64 to generate a pulse signal (clock) of the inverter frequency f _INV. The generated clock is further divided by the second frequency dividing circuit 66 to generate a read gate pulse of frequency f _LD , that is, a capture pulse signal (line LD signal) of one line.

The pulse signal of the frequency f _INV for the inverter is input to the inverter 11 and the high frequency lighting of the fluorescent tube 10 is controlled. On the other hand, the pulse signal of frequency f _LD is CC
It is added to the D drive circuit 15, the A / D converter 18, the digital signal processing circuit 20, and the like, whereby each circuit is synchronously controlled. The CCD line sensor 14 is the CCD drive circuit 1
The frequency f _{LD of the} line LD signal controlled by
And is exposed in a cycle of, and charges corresponding to the image light are accumulated. At this time, the exposure time is controlled by the shutter value of the electronic shutter, but in any case, the image light is captured in synchronization with the lighting cycle T _INV of the fluorescent tube 10. The exposure control including the electronic shutter will be described later.

The R, G, B voltage signals read from the CCD line sensor 14 are clamped by a CDS clamp (not shown) and applied to the analog amplifier 16, where the gain is controlled. The R, G, B voltage signal for one frame output from the analog amplifier 16 is converted into a dot-sequential R, G, B digital signal by the A / D converter 18, and then a known method in the digital signal processing circuit 20. After that, white balance, black balance, negative / positive inversion, gamma correction, and the like are performed, and then stored in an image memory (not shown). A concrete signal processing process in the digital signal processing circuit 20 is described in the specification of Japanese Patent Application No. 6-72079, which is not described in detail in this specification.

The R, G, B digital signals for one frame stored in the image memory are repeatedly read and converted into an analog signal by a D / A converter (not shown), and then an NTSC composite image is produced by an encoder. It is converted into a signal and output to the monitor TV. As a result, the film image can be viewed on the monitor TV.

The film driving device engages with the spool 50A of the film cartridge 50, and the spool 50A
A film supply unit that drives the film in the normal / reverse direction, a film winding unit that winds the film 52 sent from the film supply unit, and a capstan that is disposed in the film transport path and that drives the film 52 by a motor 31. It is constituted by means for sandwiching it between 32 and the pinch roller 33 and conveying the film 52 at a desired speed. The film supply section is a spool 50A of the film cartridge 50.
1 is driven clockwise in FIG. 1 to feed the film 52 from the film cartridge 50 until the leading end of the film is wound by the film winding section.

The CPU 40 forwards / reverses, starts / stops the motor 31 through the motor speed / direction control circuit 34,
The film transport speed is controlled by pulse width modulation. Then, assuming that the speed of 9.25 mm / sec is the transportation speed when the standard film image is captured,
2x speed (4.625 mm / sec) to 16x speed (1
The speed can be controlled up to a high speed (48.0 mm / sec). It should be noted that the number of pixels in the same direction as the film transport direction of one frame changes according to the film transport speed when the period of the read gate pulse of the CCD drive circuit 15 is not changed. Double, 8 times, 16
The number of pixels at each double speed is 1792 pixels, 896 pixels, 112 pixels, and 56 pixels.

Next, an exposure control method of the film scanner constructed as described above will be described. First, the film cartridge 50 is a cartridge storage portion (not shown).
When the film 52 is fed from the film cartridge 50 and the leading end of the film is wound around the winding shaft of the film winding section (when the film loading is completed), the film 52 is pre-scanned. That is, the film 52 is conveyed in the forward direction (rightward in FIG. 1) at a high speed of 16 times, and then rewound in the reverse direction at a high speed of 16 times. During the pre-scan, dot-sequential R, G, B digital signals are fetched into the integration block 41 via the CCD line sensor 14, the analog amplifier 16 and the A / D converter 18.

Since the film transport speed is 16 times, the number of pixels in the film transport direction for one frame is 56 pixels. Further, the CCD line sensor 14 is arranged in the direction perpendicular to the film transport direction as described above.
Although it has a light receiving portion for four pixels, the number of pixels in the direction orthogonal to the film transport direction of one frame is 32 by thinning out to 1/32. FIG. 2A shows an integration area in the integration block 41 in a film image of one frame. That is, one frame (56 × 32 pixels) is divided into 8 × 8 integration areas.
1 integrates the digital signals for each integration area and outputs the integrated value to the CPU 40. Incidentally, one integration area is composed of 7 × 4 pixels.

The CPU 40 obtains an average brightness value for each of the six areas as shown in FIG. 2B based on the integrated value input from the integration block 41. Then, the photometric value for exposure control is calculated by averaging the average brightness value of the central area 1 and the brightness values of the peripheral areas close to this brightness value. still,
The average brightness value of the central area 1 is weighted more than the brightness values of the peripheral areas.

The CPU 40 calculates the photometric values indicating the brightness of each frame as described above, and these photometric values are stored in the random access memory (RAM) 4 incorporated in the CPU.
Store in 0A. The photometric value of each frame is used during exposure control when the main scan is performed for each frame. Now, the exposure control according to the present embodiment is performed by the following three means.

The CCD line sensor 14 has the electronic shutter function as described above, and the CPU 40 to C
The shutter amount is controlled via the CD drive circuit 15, and thereby the exposure time is controlled. In this embodiment, the electronic shutter has a variable shutter amount range of 10% to 10%.
It is up to 0%. The CPU 40 also controls the motor rotation speed / direction control circuit 34 and the motor 3 during the main scan.
The film 52 can be controlled to be conveyed at an arbitrary speed in the range from 1 × speed to 1/2 × speed through 1. On the other hand, a disk 35 with a slit is attached to the shaft of the motor 31, and the photodetector 36 that detects the slit of the disk 35 outputs a pulse signal indicating the rotation speed of the motor to the timing generator 60. Then, the timing generator 60 generates a pulse signal synchronized with the rotation of the motor 31 by the input pulse signal during the main scan. There are two types of pulse signals generated from the timing generator 60, one of which has a frequency f _INV
Is applied to the inverter 11 to control the high frequency lighting of the fluorescent tube, and the pulse signal of the other frequency f _LD is C
It is added to the CD drive circuit 15, the A / D converter 18, the digital signal processing circuit 20, etc., whereby the drive speed of each circuit is controlled and synchronized.

That is, the CCD driving circuit 15 changes the CCD line sensor 14 by changing the film transport speed.
The periods of the read gate pulse, shutter gate pulse, and register transfer pulse that are output to are also automatically changed. Note that the number of pixels in the same direction as the film transport direction for one frame is 896 pixels during the 1 × speed main scan, but even if the film transport speed is changed, the cycle of the read gate pulse, etc. of the CCD drive circuit 15 is automatically set. Therefore, the number of pixels does not change.

By changing the film transport speed from 1 × speed to 1/2 × speed, the exposure time is 100%.
It can be changed in the range from to 200%. In the present embodiment, the fluorescent tube 10 is lit at a high frequency with a pulse signal (clock) of the frequency f _INV added from the timing generator 60, and the surface luminance slightly changes with the cycle T _INV of the lighting frequency. In the example, the lighting frequency f _INV of the fluorescent tube 10 is set to n (n is a natural number) times the capture frequency f _LD of the CCD line sensor 14, and f _INV is 1 /
Since it is generated by dividing the frequency by n, the line LD signal and the change (flicker) of the surface brightness of the fluorescent tube 10 are completely synchronized (see FIG. 3). As a result, the exposure timing for each line is synchronized with the change in the surface brightness of the fluorescent tube 10, and there is no difference in the amount of light received for each line.

Further, the gain of the analog amplifier 16 provided after the CCD line sensor 14 is controlled by the gain control signal from the CPU 40. In this embodiment, the variable range of the amplifier gain is 6 dB to 18 dB.
(2 to 8 times). The minimum gain of this analog amplifier 16 is Is determined. Hereinafter, min (CCD rated output voltage, analog amplifier rated input voltage) will be referred to as the CCD proper output voltage. If the CCD output is the CCD proper output voltage, if the amplifier gain is set to the minimum gain, the input voltage to the A / D converter 18 becomes proper (rated input voltage) and SN
Will also be the best.

Next, a case will be described in which the electronic shutter of the CCD line sensor 14, the film transport speed, and the amplifier gain are comprehensively controlled based on the photometric value of the frame for the main scan. FIG. 4 is a graph showing an embodiment in which the electronic shutter, the film transport speed, and the amplifier gain are comprehensively controlled. The change in the set value of each parameter with respect to the negative exposure amount (photometric value), and the CCD
The relationship of the MAX output voltage of a line sensor is shown. As shown in the figure, since the negative of the under has high transmittance,
The negative carrying speed is 1 ×, the gain of the analog amplifier is the minimum gain (6 dB), and the CCD output voltage is adjusted to the CCD proper output voltage only by the control by the electronic shutter. Then, as the negative becomes over (the negative transmittance decreases), the open ratio of the electronic shutter is increased to cope with the decrease in the transmittance.

When the opening rate of the electronic shutter reaches 100%, thereafter, the light receiving amount (exposure time) of the CCD line sensor 14 is adjusted by the negative conveying speed. That is, the open rate of the electronic shutter is fixed to 100%, the amplifier gain is set to the minimum gain, and the conveyance speed is reduced as the negative becomes over. Adjustable range by transport speed is limited (1
/ 2 speed), and when the negative becomes over, the opening rate of the electronic shutter is 100% and the transport speed is the lowest speed (1
The input voltage of the A / D converter 18 becomes appropriate (rated input voltage) by fixing the input voltage to the A / D converter 18 by fixing it to (/ 2 × speed) and adjusting only the analog amplifier gain.

In FIG. 4, among the areas divided according to the magnitude of the negative exposure amount, the area is the adjustment area only by the electronic shutter, the area is the adjustment area only by the transport speed, and the area Indicates a control region only by the analog amplifier gain. Area as shown in the figure ~
In the above, since the MAX output voltage of the CCD line sensor is the CCD proper output voltage (constant), the best SN is obtained. In the area, since the MAX output voltage of the CCD line sensor does not reach the CCD proper output voltage by the amplifier gain of the analog amplifier, the SN decreases as the negative becomes over. However, since the rated input range of the A / D converter is used to the maximum, the resolution during A / D conversion does not decrease.

In the above-described embodiment, the case where the invention is applied to the film scanner has been described, but the invention is not limited to this, and the invention can be widely applied to all scanners using the fluorescent tube as the illumination means and the line sensor as the imaging means. .

[0033]

As described above, according to the scanner of the present invention, the lighting frequency for lighting the fluorescent tube for illumination at a high frequency is set to be a natural multiple of the fetch frequency of one line of the line sensor. It is possible to completely synchronize the cycle of the change in the surface brightness of the fluorescent tube caused by the exposure timing at which the line sensor accumulates the signal charge,
It is possible to eliminate unevenness in the amount of received light for each line. That is, 1
Regardless of the size of the line capture cycle, it is possible to eliminate the influence of the fluctuation of the light source light from the light amount of each line received by the line sensor, and it is possible to read the image properly even if the reading speed is increased. A good image can be reproduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of an embodiment of a film scanner to which the present invention is applied.

FIG. 2 (A) shows each integration area integrated by the integration block shown in FIG. 1, and FIG. 2 (B) shows each area for calculating a photometric value.

FIG. 3 is a graph showing the relationship between the surface luminance of the fluorescent tube and the line period in this example, (A) showing the fluorescent tube current during high frequency lighting, and (B) corresponding to the tube current. The figure which shows the relationship between the fluorescent tube surface brightness | luminance and the 1 line uptake period of a line sensor.

FIG. 4 is a graph showing an example in the case of comprehensively controlling an electronic shutter, a film transport speed, and an amplifier gain.

5A and 5B are graphs showing a relationship between a conventional fluorescent tube surface luminance and a line period, FIG. 5A is a diagram showing a fluorescent tube current in high frequency lighting, and FIG. 5B is a fluorescent tube corresponding to the tube current. The figure which shows the relationship between surface brightness and the 1-line acquisition period of a line sensor.

[Explanation of symbols]

 10 ... Fluorescent tube 11 ... Inverter 12 ... Shooting lens 14 ... CCD line sensor 15 ... CCD drive circuit 16 ... Analog amplifier 18 ... A / D converter 20 ... Digital signal processing circuit 31 ... Motor 32 ... Capstan 33 ... Pinch roller 34 ... Motor rotation speed / direction control circuit 35 ... Disk 36 ... Photo detector 40 ... Central processing unit (CPU) 41 ... Accumulation block 50 ... Film cartridge 52 ... Negative film 60 ... Timing generator 62 ... Oscillator 64 ... First frequency divider circuit 66 ... Divide by 2 circuit

Claims (3)

[Claims] 1. A fluorescent tube for illumination is lit at a high frequency, and image light obtained by illuminating with the fluorescent tube is received by each light receiving section of a line sensor, and a capture signal for one line is periodically added to each received light. A scanner for outputting electric charges accumulated in a portion as an image signal, wherein a lighting frequency for lighting the fluorescent tube at a high frequency is set to be a natural number multiple of a capturing frequency of the capturing signal of the one line. 2. The line sensor discharges unnecessary charges accumulated in each light receiving portion when a shutter gate pulse is input, and controls the generation timing of the shutter gate pulse with respect to the capture signal of the one line to control the exposure time. The scanner according to claim 1, further comprising an exposure control unit capable of controlling the exposure. 3. A fluorescent tube for illumination, a timing generator, high-frequency lighting means for turning on the fluorescent tube at a high frequency based on a clock output from the timing generator, and image light obtained by illuminating with the fluorescent tube. A light receiving section for receiving the light is arranged in a line, and a line sensor that outputs an electric charge accumulated in each light receiving section as an image signal when a capture signal of one line is periodically input; Clock 1 / n
A scanner, which divides a frequency (n is a natural number) to generate a capture signal of the line sensor.