JPH02105268A - Deciding method for desired picture signal range - Google Patents

Abstract

PURPOSE:To obtain the maximum value of a desired picture signal by picking up a picture signal corresponding to a picture element point contiguous to the boundary between a subject part and a direct radiation part and obtaining the maximum value of the picked-up picture signal. CONSTITUTION:The boundary points a1-a6 between a subject part 3 and the direct radiation parts 4 are obtained by differentiation on many segments 5 extended radially from the center C of a radiation picture. Then the picture signals corresponding to those boundary points are picked up. Based on these picked-up picture signals, the maximum value of a desired signal is obtained. Thus it is possible to accurately obtain the maximum value of the desired picture signal even in the case the boundary is not clear on a histogram between the picture signals obtained by both parts 3 and 4.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for determining the maximum value of an image signal of a subject part among image signals representing a radiographic image having a subject part and a direct radiation part. .

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. By performing image processing on this electrical signal (image signal) and then reproducing it as a visible image in a photocopy, etc., it is possible to obtain a reproduced image with good image quality performance such as contrast, sharpness, and graininess. A system has been developed (see Japanese Patent Publication No. 61-5193).

The applicant has also proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject can be recorded on recording materials such as photographic materials, CRTs, etc. A radiation image recording and reproducing system that outputs a visual image has already been proposed (Japanese Patent Application Laid-Open No. 1983-1989)
No.-12429, No. 58-11395.

No. 55-163472, No. 5B-104845, No. 55-118340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining an image signal by reading it under optimal reading conditions depending on the dose of radiation applied to the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image signal obtained by this pre-reading is analyzed, and then the above sheet is irradiated with a light beam of a higher level than the light beam used during the above-mentioned pre-reading. There is also a system configured to perform main reading to obtain an image signal by scanning the radiation image and reading it under the optimum reading conditions for this radiation image (Japanese Patent Application Laid-open No. 58-67240, 5g-67241, 5g-[ No. 17242, etc.).
Here, reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as reading gain, scale factor, or , the power of excitation light during reading, etc.

Also, the high level and low level of the light beam are, respectively.
If the intensity of the light beam irradiated per unit area of the sheet or the intensity of stimulated luminescence light emitted from the sheet depends on the wavelength of the light beam (has a wavelength sensitivity distribution), It refers to the weighted intensity after weighting the intensity of the light beam irradiated per unit area of the sheet by the wavelength sensitivity, and the method of changing the level of the light beam is to use light beams of different wavelengths. methods to use, methods to change the intensity of the light beam itself emitted from a laser light source, methods to change the intensity of the light beam by inserting or removing an ND filter, etc. on the optical path of the light beam, methods to change the beam diameter of the light beam. How to change the scanning density,
Various known methods can be used, such as a method of changing the scanning speed.

In addition, regardless of whether the system performs this pre-reading or the system that does not, the obtained image signal (including the pre-read image signal) is analyzed and the optimal image processing conditions are determined when applying image processing to the image signal. Some systems let you decide. The term "image processing conditions" as used herein is a general term for various conditions under which an image signal is subjected to processing that affects the gradation and sensitivity of a reproduced image based on the image signal. The method of determining the optimal image processing conditions based on this image signal is not limited to systems using stimulable phosphor sheets, and for example, image signals are obtained from radiation images recorded on recording sheets such as conventional X-ray films. It is also applied to the system.

In the radiation image recorded on the recording sheet, there are usually areas of the subject that were irradiated with radiation that passed through the subject (transmitted or reflected), as well as areas that were directly irradiated with radiation that did not go through the subject. exist. Of these, the part that ultimately needs to be reproduced is the subject part, so when determining the optimal reading conditions and image processing conditions, the image signal corresponding to the subject part must be directly transferred to the image signal corresponding to the radiation part. It is necessary to separate it from the signal.

Various methods have been proposed to analyze the above image signals (including pre-read image signals) and separate image signals corresponding to the subject area from image signals directly corresponding to the radiation area. A method of creating a histogram of a signal is known (for example, Japanese Patent Application No. 12658/1989).
issue).

The direct radiation area is an area where radiation is directly irradiated onto the recording sheet without passing through the subject. In addition, since the image signals obtained from the direct radiation area have large values and are irradiated in a substantially --like manner, the image signals corresponding to the direct radiation area have values that are between -. On the other hand, since the image signal obtained from the subject area is the area where the recording sheet was irradiated with radiation via the subject, the image signal obtained from the subject area is more sensitive than the image signal obtained directly from the radiation area. The average value is small, and the image signal values vary depending on each tissue of the subject.

FIG. 6 is a diagram showing an example of a histogram of an image signal obtained from a radiation image. The horizontal axis shows the value of the image signal, and the vertical axis shows the frequency of appearance of the image signal of that value.

This histogram 1 includes an area 1a formed from an image signal corresponding to the subject area and an area 1b formed from an image signal corresponding to the direct radiation area, and by detecting the depression point A, The two areas 1aSlb
It is possible to separate the image signals and extract only the image signals corresponding to the subject area.

(Problem to be solved by the invention) However, since the radiation irradiated onto the recording sheet also has spatial unevenness, the image signal obtained directly from the radiation area may vary in value. The shape of the histogram changes due to individual differences. Therefore, if a histogram with two depression points B and B' is obtained, such as histogram 1' shown by the broken line in FIG. 6, which of these depression points B and B' is the image signal of the subject area? A problem arises in that it is unclear whether the value corresponds to the maximum value of . Furthermore, there are cases where clear depression points do not appear on the histogram, as in histogram 1' shown by the dashed line in Fig. 6, and in this case as well, there is the problem that the maximum value of the image signal of the subject cannot be determined. will occur.

In view of the above-mentioned problems, the present invention provides an image signal obtained from the subject area (desired image signal) and an image signal obtained directly from the radiation area, as shown in the histograms 1' and 1' of FIG. 6 above. An object of the present invention is to provide a method for determining a desired image signal range that can accurately determine the maximum value of a desired image signal even when the boundary of the image signal is not clearly defined on a histogram.

(Means for Solving the Problems) A method for determining a desired image signal range of the present invention is based on an image signal representing a radiographic image having a subject part and a direct radiation part, and a method for determining a desired image signal range along a large number of line segments on the image. The image signal is subjected to differential processing to obtain a differential signal, the boundary between the subject area and the direct radiation area is determined by determining the peak point of the differential signal, and the pixel point in the direct radiation area adjacent to the boundary is determined. is determined for each line segment, and the maximum value of a desired image signal is determined based on the image signals corresponding to these pixel points.

(Function) The desired image signal range determination method of the present invention determines the boundary between the subject area and the direct radiation area, and then determines the pixel point in the direct radiation area adjacent to the boundary. Since the image signal is always an image signal obtained directly from the radiation area and an image signal from a part adjacent to the subject area, as mentioned above, when a clear point cannot be obtained in order to obtain the maximum value on the histogram. However, the maximum value of the desired image signal can be accurately determined based on these image signals.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 3 is a perspective view showing an embodiment of a radiation image reading device using an example of the desired image signal range determining method of the present invention. This embodiment is a system that uses a stimulable phosphor sheet and performs pre-reading.

The stimulable phosphor sheet 11 on which the radiation image has been recorded is first placed at a predetermined position by a pre-reading means 100 which performs pre-reading by scanning with a weak light beam and emitting only a part of the radiation energy stored in the sheet 11. Set. The stimulable phosphor sheet 11 set at a predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveying means 13 such as an endless belt driven by a motor 12.

On the other hand, a weak light beam 1 emitted from a laser light source 14
5 is a rotating polygon fl! which is driven by a motor 23 and rotates at high speed in the direction of the arrow. After being reflected and deflected by 1B and passing through a focusing lens 17 such as an fθ lens, the optical path is changed by a mirror 18, and the light enters the sheet 11, where it is main-scanned in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). do. Stimulated luminescent light 19 is emitted from the portion of the sheet 11 irradiated with the light beam 15 in an amount corresponding to the radiographic image information stored and recorded, and this stimulated luminescent light 19 is guided by the light guide 20. , photomultiplier (photomultiplier tube)
21 photoelectrically detected. The above light guide 20
is made by molding a light-guiding material such as an acrylic plate, and is arranged such that the linear entrance end surface 20a extends along the main scanning line on the stimulable phosphor sheet ll, and the annular shape The light-receiving surface of the photomultiplier 21 is coupled to the output end surface 20b formed in the photomultiplier 21. The above-mentioned entrance end surface 20
The stimulated luminescence light 19 that enters the light guide 20 from the light guide 20 travels through the interior of the light guide 20 through repeated total reflection, exits from the output end face 20b, is received by the photomultiplier 21, and is emitted as a luminescent light representing a radiation image. The amount of exhaust light 19 is converted into an electrical signal by a photomultiplier 21.

The analog output signal S output from the photomultiplier 21 is amplified by the logarithmic amplifier 2B, and then sent to the A/D converter 27.
is digitized to obtain a pre-read image signal Sp. The signal level of the pre-read image signal Sp is proportional to the logarithm of the amount of stimulated luminescence light emitted from each pixel of the sheet ll.

In the above-mentioned pre-reading, reading conditions such as the voltage value applied to the photomultiplier 21 and the amplification factor of the logarithmic amplifier 2B are determined so that the radiation energy accumulated in the stimulable phosphor sheet U can be read over a wide range. It is being

The obtained pre-read image signal Sp is manually inputted into the storage means 28 and is stored once. Thereafter, the pre-read image signal Sp stored in the storage means 28 is read out and inputted to the calculation means 29, and the calculation means 29 processes the pre-read image signal Sp corresponding to the subject part from among the input pre-read image signals Sp. In order to extract the signal and read the object part under appropriate reading conditions during main reading, reading conditions Gls for main reading, such as the voltage applied to the photomultiplier 21' and the amplification factor of the logarithmic amplifier 26', are determined. .

The stimulable phosphor sheet 11' for which pre-reading has been completed is set at a predetermined position in the main reading means 100', and the sheet 11' is scanned by a light beam 15' that is stronger than the light beam used for the above-mentioned pre-reading. An image signal is obtained according to the reading condition G1 determined by the main reading means 100.
Since the configuration of ' is in line with the configuration of the above-mentioned pre-reading means 100, components corresponding to each component of the pre-reading means 100 are indicated by adding a dash to the number used in the pre-reading means 100, Explanation will be omitted.

The image signal S0 obtained by being digitized by the A/D converter 27' is sent to the image processing means 50.

The image processing means 50 performs appropriate image processing on the image signal S0. The image signal subjected to this image processing is sent to the reproduction device 60, and a radiation image based on this image signal is reproduced and displayed.

Next, a method will be described in which the calculation means 29 extracts the pre-read image signal corresponding to the subject part from the pre-read image signal Sp and obtains the reading condition G1 for main reading.

FIG. 1 is a diagram showing an example of a radiation image, a pre-read image signal Sp obtained from the radiation image, and its differential value ΔSp.

On the stimulable phosphor sheet 11, a subject image 3 whose subject is a leg of a human body is photographed and recorded within an irradiation field 2. Also formed within the irradiation field 2 is a direct radiation section 4 in which the stimulable phosphor sheet Il is directly irradiated with radiation.

Along each of the many line segments 5 extending radially from the center C of the stimulable phosphor sheet 11 shown in FIG. , the point where the value of the pre-read image signal Sp suddenly rises is determined as the boundary point between the subject area and the direct radiation area.

Hereinafter, a case will be described in which a boundary point on a line segment (two line segments in the positive direction and in the negative direction) along the ξ axis among the plurality of line segments 5 is determined.

Graph A is a graph representing the value of the pre-read image signal Sp obtained from each pixel along the ξ axis.

The value of the pre-read image signal Sp of the direct radiation section 4 in which radiation is directly irradiated onto the stimulable phosphor sheet 11 in the irradiation field 2 is highest, and at the boundary between the subject section 3 and the surrounding direct radiation section 4. The value of the pre-read image signal Sp is rapidly increasing. Furthermore, the value of the pre-read image signal Sp suddenly decreases at the contour of the irradiation field 2.

Graph B is a graph obtained by differentiating the pre-read image signal Sp shown in graph A from the center C in the negative direction of ξ (leftward in the figure) and in the positive direction of ξ (rightward in the figure).

In graph B, on the line segment going from the center C to the negative direction of the ξ axis, there is a peak a that protrudes upward by more than the threshold value Th.
1 exists, and the peak a1 is located inside the image from the downwardly protruding peak b1, which is the contour point of the irradiation field 2.
The position of peak a1 is determined as a boundary point.

In graph B, a downwardly protruding peak b is a contour point of irradiation field 2 on a line segment extending from center C in the positive direction of the ξ axis.
On the inside of z, there are peaks a2 and a2' that protrude upward by more than the threshold Th. In this way, when a plurality of peak points exist within the irradiation field 2, the peak point closest to the contour of the irradiation field 2 among these peak points is determined as the boundary point. This is because, in the present invention, it is more important to reliably pick up pixel points within the direct radiation area 4, rather than accurately determining the boundary between the subject area 3 and the direct radiation area 4; This is because the number 4 is overwhelmingly formed around the image. Therefore, in the above example, peak a2 of the two peaks aZ and aZ'
is closer to the contour point b2, so the position of the peak az is determined as the boundary point. Note that there is a peak projecting above the threshold value Th up to the edge of the sheet 11 on the line segment perpendicular to the ξ axis with the center 0, and therefore the object portion 3 extends up to the edge of the sheet 11. Continuing, the edge of the sheet 11 is the irradiation field 2.
It is found as the contour points of .

As described above, the boundary point al is established for each of the many line segments 5 connecting the center C and the end of the stimulable phosphor sheet 11.
(1-1 to 6 are shown in FIG. 1) and contour points b+ (j-1 to j-8 are shown in FIG. 1).

) is required.

FIG. 2 is a diagram showing a histogram of the pre-read image signal Sp within the irradiation field 2 obtained as described above. The horizontal axis shows the value of the pre-read image signal, and the vertical axis shows the appearance frequency of each part. This histogram 6 is formed from an area 6a formed from the pre-read image signal of the subject part 3 and an area 6b formed from the pre-read image signal corresponding to the direct radiation part 4. , and two depression points E1E', it is not possible to determine the boundary between the two regions 8a and 8b from this histogram 6. Such a shape of the histogram may occur, for example, when the irradiated radiation is uneven, and the irradiation doses of the direct radiation areas 4 on both sides of the subject area 3 in the radiation image shown in FIG. This may occur when there are many soft parts such as skin.

Therefore, a pre-read image signal Sp corresponding to each pixel in the direct radiation area adjacent to each of the many boundary points al obtained as described above is picked up, and based on the picked-up pre-read image signal, the pre-read image signal Sp is The maximum value of the corresponding pre-read image signal is determined. Here, the minimum value of the picked up pre-read image signals, that is, the pre-read image signals corresponding to the part adjacent to the subject part 3 in the direct radiation part 4, is the maximum value of the pre-read image signals corresponding to the subject part 3. value. The histogram 6' indicated by the broken line in Fig. 2 is
This is a histogram of the pre-read image signal picked up as described above. This histogram 6' is composed of two peaks, the minimum value P of which corresponds approximately to the position of the depression point E. Therefore, it is determined that the pre-read image signal corresponding to the direct radiation part 4 is divided into mountains on the histogram, and the minimum value P is set to the maximum value of the region 6a formed by the pre-read image signal corresponding to the subject part 4. It is judged as the value.

Histogram 6' in the figure shows another example of the histogram of the pre-read image signal picked up as described above. In this case, it is determined that the region 6b formed from the pre-read image signal corresponding to the direct radiation part 4 is composed of only one peak on the rightmost side of the figure, and the minimum value P
' is determined to be the maximum value of the area 6a.

When the maximum value of the area 6a (maximum value of the pre-read image signal corresponding to the subject part 3) is obtained as described above, the subject part is Reading conditions Gl (see FIG. 4) are determined so that the image signals in the section 3 are read under appropriate reading conditions.

In the above embodiment, there are a plurality of depression points E in the histogram of the image, such as histogram 1' in FIG.

Although we have explained the case where E' exists, even if there is no depression point at all (even if the width of the depression point is wide) as in histogram 1' in Fig. 6, it corresponds to the object part 3 in the same way. It goes without saying that the maximum value of the region 6a can be found. Further, in the above embodiment, the minimum value of the picked up pre-reading image signal is taken as the maximum value of the area 6a, but it is not limited to this, but the maximum value of the picked up pre-reading image signal - minimum value, average value, median value, etc. The maximum value of the region 6a can be determined based on various characteristic values such as the value and the variance value.

Furthermore, in the above embodiment, the boundary points between the subject area 3 and the direct radiation area 4 were found on a number of line segments extending radially from the center C of the radiation image as shown in FIG. It is not necessary to find the boundary points on line segments extending radially from a specific point, and various changes can be made, such as finding the boundary points on a large number of line segments parallel to the ξ axis. In the embodiment shown in FIG. 1, an example was explained in which an image was formed on a part of the sheet 11 (within the irradiation field 2), but a radiation image having a subject area and a direct radiation area was formed on the entire surface of the sheet 11. Of course, the present invention can be similarly applied even if the In addition, as shown in Fig. 1, not only the case where the direct radiation area 4 is formed on both sides of the subject area 3, but also the case where the direct radiation area is formed only on one side, or the case where the direct radiation area is formed around the subject area. It goes without saying that the present invention can also be applied to cases where this invention is widely used.

In addition, in the above embodiment, an apparatus was described in which the calculation means 29 calculates the reading condition G1 for main reading. 29, the pre-read image signal S
Based on p, the image processing means 50 generates an image signal SO
The image processing conditions G2 for performing image processing on the image may be determined, and the image processing conditions determined by the calculation means 29 may be input to the image processing means 50 as shown by the broken line in FIG. In step 29, both the reading conditions and the image processing conditions may be obtained.

In the apparatus shown in FIG. 3, a pre-reading means 100 and a main reading means 10
0' are configured separately, but as mentioned above, the configuration of the pre-reading means 100 and the main reading means 100' is between the two, so it is possible to integrate the pre-reading means 100 and the main reading means 100'. May also be used for both purposes. In this case, after pre-reading, the stimulable phosphor sheet 11 may be partially moved back and scanned again to perform main reading.

When the pre-reading means and the main reading means are used, it is necessary to switch the intensity of the light beam between the pre-reading and the main reading. Various methods can be used, such as a method of switching the intensity itself.

Further, although the apparatus shown in FIG. 3 is a radiation image reading apparatus that performs pre-reading, the present invention can also be applied to a radiation image reading apparatus that immediately performs reading equivalent to the above-mentioned main reading without performing pre-reading. In this case, when reading, an image signal is obtained by reading under predetermined reading conditions, and based on this image signal, an image processing condition is determined by the calculation means. Considered when applying processing.

Furthermore, the present invention can be used not only for devices using stimulable phosphor sheets but also for devices using conventional X-ray films.

FIG. 4 is a perspective view of an embodiment of an X-ray image reading device that reads an X-ray image recorded on an X-ray film.

An X-ray film 30 on which an X-ray image has been recorded is set at a predetermined position and is transported by a film transport means 31 in the direction of arrow Y' shown in the figure.

Further, the reading light 33 emitted from the light source 32, which is elongated in the − dimension, is converged by the cylindrical lens 34, and irradiates the X-ray film linearly in the X'' direction, which is substantially perpendicular to the arrow Y'' direction. Below the X-ray film 30 irradiated with the reading light 33, the above-mentioned light beam is placed at a position where the reading light 33 transmitted through the X-ray film 30 and whose intensity is modulated by the X-ray image recorded on the X-ray film 30 is received. A MOS sensor 35 is provided in which a large number of solid-state charge conversion elements are arranged in a straight line corresponding to each pixel interval in the X'' direction of the X-ray image.
While the X-ray film 30 is transported in the direction of arrow Y' while being irradiated with the reading light 33, the OS sensor 35 uses the reading light that has passed through the X-ray film 30 to correspond to each pixel interval in the Y' direction of the X-ray image. The light is received at predetermined time intervals.

FIG. 5 is a circuit diagram showing an equivalent circuit of the MOS sensor 35.

Signals from photocarriers generated when the reading light 33 hits a large number of solid-state photoelectric conversion elements 36 are transferred to capacitors Ci (i-1, 2°...) within the solid-state photoelectric conversion elements 36.
, n). The accumulated photocarrier signals are sequentially read out by sequentially opening and closing the switch section 38 controlled by the shift register 37, thereby obtaining a time-series image signal. This image signal is then amplified by the amplifier 39 and output from its output terminal 40.

The output analog image signal is sampled and converted into a digital image signal, and then, based on the image signal, a desired image signal range is determined in the same manner as in the embodiment described above. In this embodiment, the MOS sensor 35 is replaced by a CCD.

CP D (Charge Prilng Device
It goes without saying that e) etc. can be used.

Furthermore, in reading the X-ray film, it is of course possible to scan the film two-dimensionally with a light beam in the same way as reading the stimulable phosphor sheet described above. Further, in the above embodiment, the light transmitted through the X-ray film 30 is received, but it is of course possible to be configured so that the light reflected from the X-ray film 30 is received.

As described above, the method for determining a desired image signal range of the present invention is widely applied when determining the maximum value of a desired image signal from image signals representing a radiation image having a subject portion and a direct radiation portion.

(Effects of the Invention) As explained in detail above, the desired image signal range determining method of the present invention picks up image signals corresponding to pixel points in the direct radiation area adjacent to the boundary between the subject area and the direct radiation area. Since the maximum value of the desired image signal is determined based on the picked-up image signal, even if the maximum value cannot be determined from the histogram of the image signal corresponding to the entire radiation image, the maximum value is determined based on the picked-up image signal. The value can be determined with sufficient precision for practical use, and therefore, appropriate reading conditions and image processing conditions can be determined based on the desired image signal.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a radiographic image, the pre-read image data obtained from this radiographic image, and a graph of its differential value. A diagram showing a histogram of a pre-read image signal, FIG. 3 is a perspective view of an embodiment of a radiation image reading device using an example of the radiation field recognition method of the present invention, and FIG. 4 is an X-ray film FIG. 5 is a perspective view of an embodiment of an X-ray image reading device that reads an X-ray image recorded on a M
FIG. 6, a circuit diagram showing an equivalent circuit of the OS sensor, is a diagram showing an example of a histogram of an image signal obtained from a radiation image. 1.6...Histogram 2...Irradiation field 3...
・Subject part 4...Direct radiation part 5...
・Line segment 11.11'... Stimulable phosphor sheet 19.19'... Stimulated luminescence light 21.21'... Photo multiplier 26.2
6'...Amplifier 27.27'...A/D converter 28...Storage means 29...Arithmetic means 30...X-ray film 35...MOS sensor 50...Image processing means 60... Reproducing device 100... Pre-reading means 100'...
Book reading means diagram

Claims (1)

[Claims] Based on an image signal representing a radiographic image having a subject area and a direct radiation area, differential processing is performed on the image signal along a large number of line segments on the image to obtain a differential signal, and a peak point of the differential signal is determined. The boundary between the subject area and the direct radiation area is determined by determining the boundary between the subject area and the direct radiation area, the pixel points in the direct radiation area adjacent to the boundary are determined for each line segment, and the A method for determining a desired image signal range, the method comprising: determining the maximum value of a desired image signal.