JPH03136466A - Shading correcting method - Google Patents

Abstract

PURPOSE:To reduce the capacity of a memory for correction data storage by storing a differential value to the correction data of preceding picture elements concerning the shading correction data of the picture elements follow ing the leading picture element. CONSTITUTION:A loop-up table 18 storing the shading correction data, adder 43 and memory 45 are provided. While paying attention to a fact that the change of the shading correction data is small between the adjacent picture elements, concerning the correction data to correct the prescribed picture ele ment, the differential value to the correction data of the preceding picture element is stored. Thus, for a storing means to store the correction data for correcting the deviation of photoelectric conversion sensitivity, the capacity of the means is made small.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] Taichiro relates to a shading correction method for correcting the shading characteristics of data obtained by reading a recording medium on which image information is recorded with light Nf.

[Prior Art] Conventionally, an object to be scanned on which image information has been recorded is main-scanned by a light beam deflected in a one-dimensional direction by an optical deflection means such as a galvanometer mirror, a rotating polygon mirror, or a hologram scanner. is moved in a direction substantially perpendicular to the main scanning direction to perform sub-scanning, scan the scanned object two-dimensionally, obtain light having image information, and detect this light photoelectrically to generate an image signal. Image scanning reading devices are widely used to obtain images.

In the above-mentioned image scanning reader, the photoelectric conversion element for photoelectrically detecting light carrying image information is, for example, as shown in Japanese Patent Application Laid-Open No. 62-16666. 8 comes to hold up an extended elongated photo multiplier.

However, this long photomultiplier has a sensitivity deviation along its photocathode due to manufacturing reasons.

In other words, even if the amount of light containing image information that is manually applied to the light-receiving surface of the photomultiplier is constant, the analog signal output from the photomultiplier corresponding to the amount of light is converted into D/D conversion processing. When the photoelectric conversion sensitivity is measured, there is an inconvenience that the photoelectric conversion sensitivity is not constant, as shown in measurement data 2 (shading data) in FIG.

In addition, in FIG. 5), the horizontal axis represents the light receiving surface of the photomultiplier. In this case, consider that the above-mentioned to/D conversion processing is performed at predetermined intervals! Then, the received light f of the photomultiplier is substantially divided into a plurality of photoelectric conversion regions corresponding to the pixels S and used.

Therefore, in order to eliminate the above-mentioned inconvenience, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 64-85759,
Correction data 4 (shading correction data, see FIG. 5) that makes the photoelectric conversion sensitivity a constant value is stored in advance in a look-up table (LUT), and this is used to perform A/D conversion processing at each predetermined time. This paper proposes a technical concept for correcting the sensitivity deviation by correcting the digital image data. In this case, the memory capacity of the lookup table that stores the correction data is the number of photoelectric conversion areas x the resolution of the A/D converter (the number of pits in one TiTi-taper). For example, if the number of photoelectric conversion areas is 2048, A
Considering the case where the resolution of the /D converter is 10 bits, the total number of bits is approximately 2560 bytes. Particularly in the medical field where accurate image information is required, the sensitivity of the photomultiplier is changed depending on the high voltage applied to the photomultiplier, so the type of high voltage applied is For example, if there are 16 types, the memory capacity to store the correction data is 2560 pi)
X! 6, that is, the memory capacity is about 40 bytes, which increases the cost of the device;

2. Problems to be Solved by the Invention 2. An object of the present invention is to provide a shading correction method that makes it possible to reduce the storage capacity of correction data for correcting deviations in pre-occupied photoelectric conversion sensitivity. purpose.

[Means for Solving the Problems] In order to solve the above problems, the present invention performs arithmetic processing on image data obtained by dividing image information into pixels and reading them photoelectrically using shading correction data obtained in advance. In the shading correction method, the previous shading correction data is stored as the original data for the correction data corresponding to the first pixel (as well as the correction data of the previous pixel for the correction data corresponding to the first pixel). The shading correction method stores the difference value between the first pixel and the first pixel, and when performing shading correction, the shading correction data is restored from the correction data of the first pixel and the difference data of the following pixels, and shading correction calculation processing is performed. Method.

[Operation] The shading correction method according to the present invention focuses on the fact that the change in shading correction data is small between adjacent pixels, and the correction data for correcting a predetermined pixel is compared with the correction data for the previous pixel. By storing the difference value of , the capacity of the storage means for storing correction data can be reduced.

Embodiment E] Next, an embodiment of an image scanning reading apparatus that implements the shading correction method of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral IO indicates an image scanning reading/reproducing system incorporating the image scanning reading apparatus according to this embodiment. The image scanning reading and reproducing system 10 includes a laser scanning 112 in which a light beam La scans an object to be scanned on which image information is recorded, for example, a stimulable phosphor sheet S that is conveyed in the sub-scanning direction (in the six directions of arrows). , an image reading unit 214 that photoelectrically converts light having image information obtained by scanning with the light beam La, and a synchronization signal generation unit 16 that detects the scanning position of the light beam Lb and generates a start point detection signal and a synchronization signal. A look-up table (correction data storage memory) 18 with a memory capacity of 3 (n=3) bits x 2047 = 6141 bits for deriving pre-stored shading correction data in response to a predetermined clock signal, and a look-up table (memory for storing correction data) 18 from the image reading section 14. Signal processing a (S20 and CRT which reproduces and displays the pressure signal from the signal processing unit 20 as a visible image as necessary The stimulable phosphor is basically composed of a display device 22 such as a stimulable phosphor, and when irradiated with radiation vA (χ rays, α rays, β rays, T rays, electron beams, ultraviolet rays, etc.), this radiation energy is released. A phosphor that generates stimulated luminescence according to the accumulated energy by accumulating a portion of the phosphor and then irradiating it with excitation light such as visible light, and a stimulable phosphor sheet is a phosphor that A sheet having a layer consisting of.

Therefore, after the light beam L emitted from the laser light source 24 of the laser scanning section 12 passes through the beam expander 28 and is formed into a beam diameter of a desired thickness, the light beam L is swung in the direction of arrow B. Galvanometer mirror 30 that operates and reflects light
It is reflected and deflected. As the optical deflector that reflects and deflects the light beam L in this way, in addition to the galvanometer mirror 3G, a pre-engineered rotating polygon mirror, a hologram scanner, an AOD (acousto-optic optical deflector), etc. can be used. .

1. The light beam L reflected and deflected by the action of the galvanometer mirror 30 passes through a scanning lens 32 such as an fθ lens arranged on the optical path! After a, the light enters a half mirror 34 which extends in the main scanning direction on the optical path. This half mirror 34 outputs the incident light beam L, reflects an amount of light beam necessary for scanning as a scanning light beam La, and transmits the remaining light beam as a synchronization light beam Lb. Reflected scanning light beam L
The light a converges on the stimulable phosphor sheet S disposed on the optical path, and scans the stimulable phosphor sheet S in the main scanning direction (arrow C direction).

The image reading unit 14 is a long photomultiplier (photoelectric converter) whose main body extends in the main scanning direction to photoelectrically convert the stimulated luminescent light emitted from the stimulable phosphor sheet S excited by the light beam La. means) 36 and a light guide 38 that guides the stimulated luminescent light to the light receiving surface of the photomultiplier 36. In this case, the light receiving surface of the light beam La in the photomultiplier 36 is arranged close to the stimulable phosphor sheet S along its main scanning direction. A high voltage generator 4 is applied to the high voltage input terminal of the photomultiplier 36 based on the specified reading sensitivity.
A zero output signal is introduced. Frit multi-briar 36
The pressure after 0 photoelectric conversion is introduced into one input terminal of an adder 42 in the signal processing section 20 via a log amplifier 41. The other input terminal of the adder 42 is
The shading correction data output from the previous 8-digit backup table 18 is sent via an adder 43, a 110-pit memory (memory for storing 10 (N=10) pit shading data) 45, and a D/A converter 47. The signal is then introduced as a shading correction signal. The output signal of the adder 42 is sent to an A/D converter (A
/D conversion means) 44 is introduced into the signal input terminal.

On the other hand, in the synchronization signal generating section 16, a transmission section 46a that transmits the light beam Lb that has passed through the half mirror 34 and a reflection section 546b that reflects the light beam Lb are arranged alternately along the scanning direction of the light beam Lb. a cylindrical light guide 50 disposed along the rear of the grid 46; and an optical sensor provided at both ends of the light guide 500 for detecting the light beam Lb transmitted from the grid 46. 52a, 52b and the optical sensor 52
The synchronization signal generator 54 generates a sampling clock S including a start point detection signal based on a grid clock S6 outputted from the grid clocks S6 and 52b, and a read clock Sm for reading the lookup table 18 and the like. A wide transparent section (not shown) is formed at the top of the grid 46 in order to detect the starting point of the effective scanning position of the stimulable phosphor sheet S.

Among the clock signals generated from the synchronization signal generator 54, the sampling clock Ss is introduced into the synchronization signal input terminal of the A/D converter 44. - side, read clock Sm
is introduced into a lookup table 18 in which 3-bit shading correction data is stored, and the 3-bit shading correction data stored in the lookup table 18 is read out based on the designated read sensitivity and the read clock St. , are introduced into one input terminal of the adder 43.

The other input terminal of this adder 43 receives from the memory 45,
As will be described later, 10-bit correction data relating to one pixel before a predetermined pixel in the main scanning direction is introduced. Then, 10-bit correction data related to the predetermined pixel is derived from the adder 43, and is sent to the memory 45 and the D/Δ converter 4.
7 to the other input terminal of the adder 42 as an analog correction signal corresponding to 10-bit shading correction data. Therefore, adder 4
A signal after shading correction is derived from A/D converter 44 from A/D converter 44 .

The signal input to the A/D converter 44 is quantized and digitized every sampling clock Ss. The A
The output digital data from the /D converter 44 is subjected to processing such as gradation processing and frequency processing by the image processor 58, and then stored in the image memory 60. Next, based on the image signal recorded in the image memory 60, a reproduced image is formed as a visible image on a display device 22 such as a CRT via a D/A converter 62 as required.

Figure 2 is number 1! ! FIG. 2 is a block diagram showing a schematic configuration of a synchronization signal generator 54 shown in FIG. This vA synchronization signal generator 54
is basically configured as a frequency synthesizer. In FIG. 2, a grid clock S is introduced into one input terminal of a phase comparator 64, and the output signal of the phase comparator 64 is introduced into an input terminal of a voltage controlled oscillator 68 via a low-pass filter 66. The output signal of voltage controlled oscillator 68 is passed through first divider 70 to lookup table 18.
The clock signal S is outputted as a read clock S for reading data from, etc., and is also introduced into the second divider 72. One output signal of the second divider 72 is output to the phase comparator 64.
The other output signal is introduced as the sampling clock S to the synchronizing signal input terminal of the A/D converter 44. The second divider 72 is provided with a switch 74 that can change the frequency division ratio according to the reading area of the stimulable phosphor sheet S, for example, large square, six-cut, four-cut, etc. reading area.

The image scanning reading and reproducing system incorporating the image scanning reading apparatus according to this embodiment is basically constructed as described above, and its operation will be explained in detail next.

First, generation of shading correction data stored in lookup table 18 and memory 45 will be explained. In this case, a reference stimulable phosphor sheet S whose entire surface is uniformly exposed to X-rays is prepared, and a photomultiplier is used to read the stimulated luminescence of the stimulable phosphor sheet S6. Shading data may be obtained by applying a predetermined high voltage to 36, and shading correction data may be obtained by performing predetermined arithmetic processing on this shading data.

That is, on the right side of FIG. 1, the reference stimulable phosphor sheet (So), which is uniformly exposed to X-rays, is transported in the sub-scanning direction A by a transport mechanism (not shown). On the other hand, the reference stimulable phosphor C)S.

The light beam La emitted from the laser light source 24 is on the surface of
By being irradiated in the main scanning direction, the --like image information recorded on the reference stimulable phosphor So is extracted as stimulated luminescence light.

This stimulated luminescent light is produced by the standard stimulable phosphor C)S.

The light enters the photomultiplier 36 via a light guide 38 disposed in the main scanning direction, and is converted into an electrical signal.

The output signal from the photomultiplier 36 is then introduced into a signal input terminal of an A/D converter 44 through a log amplifier 41 and an adder 42 whose other input terminal receives a zero signal.

On the other hand, the light beam Lb that has passed through the half mirror 34 is incident on the grid 46 that constitutes the synchronization signal generator 16 . Next, the light beam Lb is scanned in the direction of the arrow B by the swinging operation of the galvanometer mirror 30 in the direction of the arrow B;
Move from one end of the grid 46 to the other end. In this case, the light beam Lb that passes through the grid R46a8 is incident on the light guide 50. And the light beam Lb
is repeatedly reflected by a diffusion band (not shown) formed on the side opposite to the incident side of the light beam Lb of the light guide 50, reaches the optical sensors 52a, 52b (:lIJ), is photoelectrically converted, and is converted into a grid clock. s6 is generated.

At the leading end (not shown) of the grid clock S, there is a grid clock S whose phase is modulated by a wide transparent part existing at the starting point of the grid 46.

Therefore, the A/D converter 44 can take in an analog signal using the wide pulse related to this phase modulation section as an effective scanning start area on the main scanning line. In this case, the output signal of the voltage controlled oscillator 68 is the signal input to the phase comparator 64, that is, the grid clock S.

For example, the frequency signal is multiplied by 24, and the division ratio of each of the second dividers 72 is set to 4.6.8 corresponding to the reading size, for example, large angle, quarter cut, and six cut. If it is determined, the sampling clock Ss is an output signal whose frequency is multiplied by 4 times, 6 times, or 8 times with respect to the grid clock SG. Note that the read clock St for shading correction is generated with the frequency division ratio of the first divider 700 being 4. Therefore, in order to generate the shading correction data stored in the look 7 bup table 18, the reading sampling clock Ss is changed to the read clock Ss.
Large-angle reading sampling clock Ss with the same period as t
(Second divider 720 frequency division ratio=4).

As a result, the large-angle read sampling clock Ss
The analog signal input to the A/D converter 44 is A/D converted for each clock pulse of the image processor 58.
Data is stored in the image memory 60 via. In this case, the data stored in the image memory 60 is obtained as data DS, for example, as shown by the dotted line in FIG.

The horizontal axis of the characteristic curve shown in Figure 3 is the photomultiplier 3.
6 corresponds to the light receiving surface, that is, the photoelectric conversion area along the main scanning direction C, and the vertical axis represents the deviation of the photoelectric conversion sensitivity, that is,
Therefore, the data DS becomes shading data DS. In addition, in Fig. 3, A/
The D conversion processing is performed in rows r every sampling clock Ss; thereby, an image signal divided into one for each pixel is obtained corresponding to the previous eight sampling clocks 5sr. In this case, it is assumed that the number of surface element divisions per main scanning line is 2048 pixels.

Note that the shading data DS includes a photomultiplier 36 that constitutes the image scanning reading/reproducing system 10.
and all characteristics of the optical system such as the galvanometer mirror 30 and the light guide 38.

Therefore, the shading correction data DI to be stored in the lookup table 18 and the memory 45 is as shown by the solid line in FIG.
With respect to S, shading correction data DI is assumed to be line-symmetrical in the drawing with respect to a predetermined value K of sensitivity. In other words,
The sum of the shading data DS and the shading correction data DI for each pixel is converted to a constant value without deviation and stored.

However, as for the number of bits of the correction data, as can be understood from the schematic diagrams in FIG. 3 and 41iIJA and B,
For the first pixel), 10-bit shading correction data χ1 is stored in the memory 45, and the second
For each pixel, shading correction data Δ1, which is the difference between the 10-bit shading correction data χ1 for the first pixel and the 10-bit shading correction data χ2 for the second pixel, is stored in the first pixel of the lookup table 18.
Store at memory address m. Using a long photomultiplier, it has been confirmed that the number of levels of the radiation image power (to read the accumulated stimulable phosphor sheet, the difference data Δ) is within 3 levels of the lattice. Therefore, as shown in FIG. 4, the shading correction data Δ, including the sign bit, may be 3-bit data.In this way, the shading correction data Δ for the second and subsequent pixels.

As Δ2° 41, 3-bit data corresponding to the difference between a predetermined pixel and the previous pixel are stored at memory addresses m2 to m, respectively. , 1.

Next, the image is actually recorded on the stimulable phosphor sheet)S.
1 is set in the image scanning reading/reproducing system IO, and a predetermined high voltage is applied to the photomultiplier 36 to read the image. In this case, the high voltage is set based on the specified read sensitivity, and therefore the memory 45, lookup table 1
The shading correction data DI related to the predetermined high voltage stored in 8 is selected, and this shading correction data DI is read out every read clock S1. Here, the shading correction data for the first pixel is as follows:
As described above, the shading correction data χ1 is read out from the memory 45, the shading correction data χ1 is introduced into the D/A converter 47, and the analog signal corresponding thereto is introduced into the other input terminal of the adder 42. shading correction.

Next, for the second pixel, lookup table 18
The 3-bit correction data Δ1 is introduced from the memory address m1 of 2 to the adder 43, and the adder 43 inputs the correction data 2. After being added to the shading correction data Z++ and stored in the memory 45, the data related to the shading correction data Z++Δ is added to D/
The signal is introduced into the adder 42 via the A converter 47. In this way, shading correction data χi,l are sequentially derived, generally as shown in the following equation (1).

χmu, 1 = χ1 + Δkame (i=1~2047)
... [1) That is, the shading correction data z for the i+1st pixel (i+1) among the pixels!
, 1 is the pixel one area before the shading correction data 2. and the 3-bit correction data Δ1 are added to the adder 42, and the shading is corrected.

In this case, according to this embodiment, the amount of correction data stored in the memory 45 and the lookup table 1B is determined by the amount of lO applied to the first pixel as shown in the following equation (2).
The number of pits is the sum of the bit data and 3 bits x 2047 data relating to the second to 2048th pixels, and is approximately 770 bytes of data.

Therefore, the memory capacity of the correction data storage memory is reduced to approximately 1/3 compared to the prior art described above.

10 bits + 3 bits x 2047, 6151 bits - 770 bytes...(2)
[Effects of the Invention] As described above, according to the present invention, by focusing on the fact that the change in shading characteristics between adjacent pixels is relatively small, the shading correction data of the pixel following the first pixel is calculated based on the shading correction data of the previous pixel. By storing the difference value from the correction data, it is possible to reduce the capacity of the memory for storing the correction data.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an image scanning reading and reproducing system in which the direct image scanning reading device according to the present embodiment is incorporated; Fig. 2 is a detailed block diagram of the counting signal generator shown in Fig. 1; Fig. 3; 4 is a schematic diagram illustrating the memory capacity of a memory for storing fading correction data. FIG. 5 is a diagram illustrating the operation of creating correction data in a general photo multiplier. It is. ...Reference stimulable phosphor sheet...Grid clock...Sampling clock...Read clock 10...Image scanning reading/reproducing system 12...Laser scanning unit 14...Image reading unit 16...・Synchronization signal generation capability 18... Lookup table 20... Signal processing B 24... Rade light source 28...
Beam expander 30... Galvanometer mirror 45... Memory 46... Grid L
, La, Lb...light beam S...stimulable phosphor sheet

Claims (1)

[Claims] (1) In a shading correction method in which image data obtained by dividing image information into pixels and reading them photoelectrically is subjected to arithmetic processing using shading correction data obtained in advance, the shading correction data corresponds to the correction data corresponding to the first pixel. stores the original data and
1 for the correction data corresponding to the pixels following the first pixel.
The difference value between the previous pixel and the correction data is stored, and when performing shading correction, the shading correction data is restored from the correction data of the first pixel and the difference data of the following pixel, and shading correction calculation processing is performed. shading correction method.