JP2004201783A - Image processor, image processing method, and x-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor, for converting an X-ray tomographic image recorded on an X-ray film to digital data reproducing CT value with high reliability in digitization. <P>SOLUTION: This image processor for processing an X-ray tomographic image of a subject obtained by X-ray irradiation includes: an input part 201 or 202 for inputting the X-ray tomographic image recorded on the film as image data; an extract part 204 extracting the luminance value in a designated position of the image data; a luminance data conversion part 205 for converting the luminance value of the image data according to the extracted luminance value in the designated position; a character recognition part 203 for recognizing information on WL and WW on the image data; and a CT value data conversion part 206 for converting the image data converted to the luminance data to CT value according to the recognized information on the WL and WW. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus for processing an X-ray tomographic image of a subject obtained by X-ray irradiation, and an X-ray CT (Computerized Tomography) apparatus including the image processing apparatus.
[0002]
[Prior art]
In general, an X-ray tomographic image of a subject obtained by X-ray irradiation is stored on a magneto-optical disk as a digital image, or is recorded and stored on a video tape as film or analog data. In particular, many hospitals and the like often store X-ray tomographic images on film.
[0003]
However, while these media are easy to handle, they also have problems such as requiring a space for storage. With the spread of medical image filing systems, when it is desired to compare with current X-ray tomographic images, a film is read by an image reading device such as a scanner, or A / D conversion is performed on data recorded as analog data on a video tape. Thus, there may be a case where the image data (digital data representing a grayscale image) is stored again on a hard disk or the like. For example, in Japanese Patent Application Laid-Open No. H11-163, the data obtained by the diagnostic apparatus is reconstructed and displayed as an image, and is stored in a database via a communication network. A technique has been disclosed that enables image reconstruction of a desired specific area by sending configuration parameters.
[0004]
[Patent Document 1]
JP-A-63-109843
[Problems to be solved by the invention]
However, there are some problems when saving as image data, and the details will be described below.
[0006]
Generally, when reconstructing an X-ray tomographic image, a window operation for allocating a predetermined luminance value is performed based on the calculated CT value. The window operation refers to displaying a grayscale image by a CT value having a certain width called a window width (WW) centering on a certain CT value set as a window level (WL).
[0007]
This is because many CT values of each tissue in the human body are distributed between 0 and 100, and CT values from -1000 (air) to +1000 are displayed on the same scale. However, when the CT value to be noted is around 0 to 100, the gradation difference is not so visible, and is not clinically meaningful.
[0008]
The above-mentioned WL and WW may be individually set at the time of capturing an X-ray tomographic image. Between X-ray tomographic images having different settings of WL and WW at the time of capturing, the luminance value on the X-ray film is different. Even if they are the same, they do not always have the same CT value and cannot be simply compared. If such assumptions are disregarded and image data is formed, it is sometimes difficult to perform comparative reading of X-ray tomographic images taken at different dates and times. This is because in diagnosis where comparison with past image data is important. It is a big problem.
[0009]
As described above, an X-ray film requires an image reading device such as a scanner when storing it as image data, and an A / D image is recorded on a video tape as analog data. Although a video input interface as a converter is required, the accuracy (luminance gradation resolution) of both is not always the same. For this reason, similarly to the above, even if the luminance value is the same on the image data, it does not necessarily have the same CT value, and when an X-ray tomographic image recorded on a different medium is converted into image data, Also, there is a problem that the image data cannot be simply compared with each other.
[0010]
Furthermore, even if the medium is the same X-ray film, there is a difference in the luminance value between the one that has been slightly deteriorated due to aging or the like and the other that has not, and depending on the type of scanner used to read the X-ray tomographic image. Also, the luminance value of the image data differs.
[0011]
As described above, even if an X-ray tomographic image recorded on an X-ray film or an X-ray tomographic image recorded on a video tape as analog data is stored as image data, the validity of the data is poor in the conventional method. For this reason, it is desired to store the data by reproducing a highly reliable CT value.
[0012]
The present invention has been made in order to solve the above-mentioned problems, and is directed to converting an X-ray tomographic image recorded on an X-ray film or an X-ray tomographic image recorded on a video tape as analog data into digital image data. It is an object of the present invention to provide an image processing apparatus capable of converting a highly reliable CT value into digital image data reproduced and an X-ray CT apparatus including the image processing apparatus.
[0013]
[Means for Solving the Problems]
An X-ray CT apparatus according to the present invention for solving such a problem has the following configuration. That is,
An image processing apparatus for processing an X-ray tomographic image of a subject obtained by X-ray irradiation,
Input means for inputting the X-ray tomographic image recorded on the film as image data,
Extracting means for extracting luminance information of a predetermined position of the image data, and luminance conversion means for converting a luminance value of the image data based on the extracted luminance information of the predetermined position,
Recognition means for recognizing information about a window level and a window width described on the image data,
CT value conversion means for converting the brightness-converted image data into a CT value based on the recognized information on the window level and the window width.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a plurality of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be noted that the same reference numerals indicate the same or corresponding parts throughout the drawings.
[0015]
[First Embodiment]
<Overall system configuration>
FIG. 1 is a system configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention. In an X-ray CT apparatus, an X-ray source that generates X-rays rotates around a subject (patient), and X-rays at different irradiation angles transmitted through the patient are detected by an X-ray detector. The image (X-ray tomographic image) of the tomographic plane (the plane at the slice position, that is, the slice plane) of the X-ray irradiation site is obtained (reconstructed) by computer processing on the operation console.
[0016]
As shown in FIG. 1, the X-ray CT apparatus includes a gantry 120 for irradiating a subject (patient) with X-rays and detecting X-rays transmitted through the placed subject, and instructs the gantry 120. A signal is transmitted to make various settings, and an X-ray tomographic image is reconstructed and projected based on the projection data output from the gantry 120, and the operation console 100 for displaying the image and the subject are placed and transported to the inside of the gantry. And a transfer device 140.
[0017]
The gantry 120 has the following configuration including a main controller 122 that controls the entire system.
[0018]
Reference numeral 121 denotes an interface for performing communication with the operation console 100, 132 denotes a gantry rotating unit, and inside thereof, an X-ray tube 124 that generates X-rays that are driven and controlled by an X-ray tube controller 123, an X-ray tube controller 123, a collimator 127 that defines an X-ray irradiation range, adjustment of a slice value that defines an X-ray irradiation range of the collimator 127, and a Z-axis direction of the collimator 127 (a direction perpendicular to the drawing, that is, A collimator motor 126 for adjusting the position (in the direction of being conveyed toward the hollow portion 133) is provided. The driving of the collimator motor 126 is controlled by a collimator controller 125.
[0019]
The gantry rotating unit 132 includes an X-ray detection unit 131 that detects X-rays transmitted through the subject, and a data collection unit 130 that collects projection data obtained by the X-ray detection unit 131. Note that the X-ray detection unit 131 includes a plurality of detector rows each having a detection element group including a plurality of detection elements (channels) arranged in the Z-axis direction.
[0020]
The X-ray tube 124, the collimator 127, and the X-ray detection unit 131 are provided at positions facing each other with the hollow portion 133 interposed therebetween. It works. This rotation is performed by a rotation motor 129 whose rotation speed is controlled at a predetermined control cycle by a drive signal from a rotation motor controller 128.
[0021]
Further, the transport device 140 has a top plate 142 on which the subject is actually placed, and a table 143 holding the top plate 142, and the top plate 142 is driven in the Z-axis direction by a top plate motor 141 (ie, The driving of the top motor 141 is controlled at a predetermined control cycle based on a drive signal from the top motor controller 134.
[0022]
The main controller 122 analyzes various instruction signals received via the I / F 121, and based on the analysis, the X-ray tube controller 123, the collimator controller 125, the rotary motor controller 128, the top motor controller 134, and the data Various control signals are output to the collection unit 130. The main controller 122 also performs a process of transmitting the projection data collected by the data collection unit 130 to the operation console 100 via the I / F 121.
[0023]
The operation console 100 is a so-called workstation, as shown in the figure, including a CPU 105 that controls the entire apparatus, a ROM 106 that stores a boot program and the like, a RAM 107 that functions as a main storage device (memory), and the following components. Is provided.
[0024]
The HDD 108 is a hard disk device in which an OS and a diagnostic program for controlling the entire X-ray CT device are stored. Note that a control program for realizing the image processing method according to the present invention on the operation console 100 is also stored in the HDD 108. Then, the CPU 105 reads and executes the control program, whereby the image processing method according to the present invention is achieved. In this case, the program code itself read from the HDD 108 implements the image processing method, and the HDD 108 storing the program code constitutes the present invention.
[0025]
Return to FIG. The VRAM 101 is a memory for developing image data (256 × 256 pixels) to be displayed. By developing the image data and the like in this memory, an X-ray tomographic image can be displayed on the CRT 102. Reference numerals 103 and 104 denote a keyboard and a mouse for performing various settings. An interface 109 communicates with the gantry 120.
[0026]
A scanner I / F 110 can be connected to a scanner for taking in an X-ray film. Reference numeral 111 denotes a video I / F for taking in an analog video signal from a VTR that reproduces a video tape on which an X-ray tomographic image is recorded as analog data, and performs A / D conversion on the taken-in analog video signal. It is possible.
[0027]
<Description of image processing method>
Next, an image processing method according to an embodiment of the present invention will be described using a functional block diagram (FIG. 2) showing functions of a program for realizing the above-described image processing method and a flowchart (FIG. 3) showing a processing flow. Will be described in detail. In the following, a case in which an X-ray film is converted into digital data will be mainly described. However, the processing is basically the same for a video tape recorded as analog data.
[0028]
In FIG. 2, reference numeral 202 denotes a video signal input unit; 201, a scanner signal input unit; and a video data signal input unit 202, which converts image data A / D converted by the video I / F 111 into a scanner signal input unit 201. Reads the image data captured by the scanner I / F 110.
[0029]
Reference numeral 205 denotes a character recognition unit that recognizes characters (WL, WW) described in a predetermined position in image data read from the video signal input unit 201 or the scanner signal input unit 202 in advance. Generally, set values of WL and WW at the time of photographing the X-ray film are printed on the X-ray film. FIG. 4 is a diagram showing an example of the X-ray film. In the lower left end portion of the X-ray film 401, “WW: xxx”, “WL: xxx” (xxx portions) Has a specific CT value written therein). The character recognizing unit 205 recognizes WL and WW (characters in the xxxx portion) using existing character recognition technology.
[0030]
203 is a maximum luminance value / minimum luminance value extraction unit. That is, the maximum luminance value and the minimum luminance value of the read image data are extracted from the area where the characters “WL” and “WW” are printed, respectively. Reference numeral 403 in FIG. 4 is an enlarged version of the character “W” of WW or WL on the X-ray film 401. For example, the white portion (403- The luminance value of 1) is extracted as the maximum luminance value. Further, the luminance value of the shadow portion (403-2) of the hollow character is extracted as the minimum luminance value.
[0031]
The white portion 403-1 is originally printed on the X-ray film as white (that is, luminance value 255), and the shadow portion 403-2 is originally black (that is, luminance value 0). Printed on line film. Therefore, the luminance value 255 or the luminance value 0 should be indicated on the read image data. However, the luminance value range may vary depending on various factors such as deterioration of the X-ray film and luminance resolution at the time of reading by the scanner. May be narrow. Therefore, by performing luminance data conversion (normalization) on the basis of the luminance values of these characters on the image data, it is possible to reproduce the original luminance value range (range). The luminance data conversion unit 205 performs such luminance data conversion processing.
[0032]
206 is a CT value data conversion unit. In the CT value data conversion unit, the luminance data conversion unit 204 calculates a CT value corresponding to the luminance value of each pixel using the image data converted to the original grayscale image, and converts the CT value into CT value data. I do.
[0033]
More specifically, the determination is performed using the WW and WL (the numbers in the xxx part) recognized by the character recognition unit 205 and the graph shown in FIG. The CT value can be determined from the luminance values of 0 to 255.
[0034]
FIG. 5 shows the CT value on the horizontal axis and the luminance value on the vertical axis. The polygonal line 501 is 0 when the CT value is smaller than (WL-WW / 2), and (WL-WW / 2). ) Or more and (WL + WW / 2) or less, there is a linear relationship with the luminance value between the luminance value 0 and the luminance value 255, and when the CT value is larger than (WL + WW / 2), it is 255.
[0035]
That is, when an X-ray film corresponding to the image data is photographed, a CT value between WL-WW / 2 to WL + WW / 2 is assigned as a luminance value from 0 to 255. If the luminance data converted in step 204 is converted into CT values according to the relationship shown in FIG. 5, the original CT values can be reproduced.
[0036]
Reference numeral 207 denotes a storage unit which instructs the HDD 108 to store digital data including the CT values reproduced by the CT value data conversion unit 206.
[0037]
FIG. 3 shows a flow of processing of each functional block in the functional block diagram shown in FIG. In step S301, image data is input from the scanner signal input unit 202.
[0038]
In step S302, the maximum luminance value and the minimum luminance value are extracted from the input image data. In step S303, the analog image read by the scanner is read based on the maximum luminance value and the minimum luminance value. The image data is digitized by subjecting the data to AD conversion and performing luminance data conversion processing (normalization).
[0039]
In step S304, the character recognition unit 205 recognizes the characters WL and WW, and also recognizes the CT value described.
[0040]
In step S305, the range of WL-WW / 2 and WL + WW / 2 is divided into 256 equal parts using the CT values of WL and WW with respect to the digital image data that has undergone the luminance data conversion, and the digital image data of 0 to 255 is obtained. A CT value data conversion process for converting data into CT is performed.
[0041]
In step S306, the digital data converted into the CT value data is stored in the HDD. In addition, it is also possible to display digital data converted into CT value data as image data (CT value image data) according to an instruction of the operator.
[0042]
As is apparent from the above description, according to the present embodiment, when converting an X-ray tomographic image recorded on a medium such as an X-ray film into digital data, an image is formed based on the luminance value of a WL or WW character. After converting (normalizing) the data to the original luminance value, the range of WL-WW / 2 and WL + WW / 2 is divided into 256 equal parts, and the digital image data of 0 to 255 is converted to the CT value. Thus, conversion to CT image data that reproduces a highly reliable CT value becomes possible.
[0043]
[Second embodiment]
In the first embodiment, when the CT value data conversion unit 206 changes the image data into CT value data, the linear graph indicated by 501 in FIG. 5 is used, but the present invention is not limited to this. A non-linear graph according to the characteristics of the film as shown in FIG. 502 may be used. In any case, during X-ray film radiography, by using the same conversion method as that used to determine the luminance value from the CT value, it is possible to convert the CT value into CT image data that reproduces highly reliable CT values It becomes.
[0044]
[Third Embodiment]
In the first embodiment, when extracting the maximum brightness value and the minimum brightness value, the white portion 403-1 and the shadow portion 403-2 of the character “WL” or “WW” recognized by the character recognition unit 205. However, the present invention is not limited to this, and a gray scale printed on an X-ray film may be used.
[0045]
FIG. 6 shows an example of an X-ray film with a gray scale. The maximum luminance value and the minimum luminance value in the gray scale 602 shown at the left end of the X film 601 are extracted from the read image data. Is also good.
[0046]
[Fourth embodiment]
In the first embodiment, when performing the CT value data conversion processing in the CT value data conversion unit 206, the “brightness value-CT value graph” shown in FIG. 5 is used. However, the present invention is not limited to this. A corrected “luminance value-CT value graph” may be used so that the CT value of air does not become −1000 or less according to the CT values of WL and WW recognized by the unit 205.
[0047]
FIG. 7 is a flowchart illustrating a flow of image processing in the X-ray CT apparatus according to the present embodiment. In FIG. 7, steps S301 to S304 are the same as those in the flowchart of FIG.
[0048]
In step S701, (WL-WW / 2) is calculated based on the WL value and WW value recognized in step S304, and it is determined whether the calculation result is greater than -1000. (WL-WW / 2) should originally be equal to the CT value of the air portion (that is, -1000). If the calculation result is larger than -1000, the process proceeds to step S702, and the "luminance value -CT value graph "is corrected.
[0049]
FIG. 8 is a diagram for explaining the details of the correction process of the “brightness value-CT value graph” (FIG. 8A is the same as FIG. 5). As shown in FIG. 8A, consider the case where the value of (WL-WW / 2) is larger than -1000.
[0050]
Now, in the image data subjected to the luminance data conversion processing in the luminance data conversion processing (step S303), the image data having a luminance value of 0 has a CT value of (WL-WW / 2) according to FIG. Will be converted. However, since a portion having a luminance value of 0 on the image data is an air portion, the CT value is preferably converted to -1000.
[0051]
Thus, the graph shown in FIG. 8B is corrected by a “brightness value-CT value graph” correction process. In the present embodiment, all luminance values equal to or less than 80 are regarded as air portions, and correction is performed so that the CT value is converted to -1000. The polygonal line 801 is a graph after correction. According to the graph, when the brightness is equal to or less than a predetermined luminance value, all the CT values are converted to -1000.
[0052]
Referring back to FIG. In step S703, a CT value data conversion process is performed. At this time, if “NO” is determined in step S701, CT value data conversion processing is performed using a conversion formula as usual, and if “YES” is determined, “luminance” illustrated in FIG. Using the "value-CT value graph", the CT value data conversion is fixed at -1000.
[0053]
In step S306, the digital data converted into the CT value data is stored in the HDD.
[0054]
As is clear from the above description, according to the present embodiment, -1000 is secured for the CT value of the air portion.
[0055]
[Fifth Embodiment]
In the first embodiment, the digital data obtained by performing the CT value data conversion processing in the CT value data conversion unit 206 is stored in the HDD 108 as it is. However, the present invention is not limited to this. An error message may be output.
[0056]
FIG. 9 is a flowchart illustrating a flow of image processing in the X-ray CT apparatus according to the present embodiment. In FIG. 7, steps S301 to S305 are the same as those in the flowchart of FIG.
[0057]
In step S901, (WL + WW / 2) is calculated based on the WL value and WW value recognized in step S304, and it is determined whether the calculation result is smaller than 1000. If the calculation result is smaller than 1000, there is a high possibility that the bone portion or the like does not have a correct CT value. Therefore, the process proceeds to step S902, an error message is output, and the digital data after the CT value data conversion processing is output. That effect is written in the file header, and in step S306, the digital data is stored in the HDD.
[0058]
[Sixth Embodiment]
In each of the above embodiments, the image processing method according to the present invention is realized by the operation console of the X-ray CT apparatus. However, the present invention is not limited to this, and may be realized by an independent operation console (image processing apparatus). Good. FIG. 10 shows an example of an image processing apparatus for realizing the image processing method according to the present invention. Note that the image processing apparatus illustrated in FIG. 10 has the same configuration as the operation console 100 of the X-ray CT apparatus in FIG. 1 except for the NET I / F 112, and thus a detailed description is omitted here.
[0059]
Further, the image processing apparatus is not limited to the one shown in FIG. 10 and may have another image processing function. Further, it may be connectable to a network. In that case, for example, PACS (Picture Archiving / Communicating System) (a comprehensive medical image information system in a hospital. Medical image information is centrally stored on a magneto-optical disk or the like) NET I / F 112 in FIG. 10 is an I / F for performing communication with an external network. Yes, an X-ray tomographic image can be converted into digital data by an image processing device and transmitted to the PACS via the NET I / F 112.
[0060]
[Other embodiments]
In the above embodiment, the HDD is used as the storage medium for supplying the program code. However, the present invention is not limited to this. For example, a floppy (registered trademark) disk, an optical disk, a magneto-optical disk, a CD-ROM , CD-R, magnetic tape, non-volatile memory card, ROM, and the like.
[0061]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0062]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0063]
【The invention's effect】
As described above, according to the present invention, when converting an X-ray tomographic image recorded on an X-ray film or an X-ray tomographic image recorded on a video tape as analog data into digital data, a highly reliable CT is used. The value can be reproduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is a functional block diagram illustrating functions of the X-ray CT apparatus according to the first embodiment of the present invention.
FIG. 3 is a flowchart illustrating a flow of image processing in the X-ray CT apparatus according to the first embodiment of the present invention.
FIG. 4 is a diagram showing an example of an X-ray film.
FIG. 5 is a diagram illustrating a relationship between a CT value and a luminance value used when a CT value data conversion unit in the X-ray CT apparatus according to the first embodiment of the present invention performs a conversion process.
FIG. 6 is a diagram showing an example of an X-ray film.
FIG. 7 is a flowchart illustrating a flow of image processing in an X-ray CT apparatus according to a fourth embodiment of the present invention.
FIG. 8 is a diagram illustrating a relationship between a CT value and a luminance value used when a CT value data conversion unit in an X-ray CT apparatus according to a fourth embodiment of the present invention performs conversion processing.
FIG. 9 is a flowchart illustrating a flow of image processing in an X-ray CT apparatus according to a fifth embodiment of the present invention.
FIG. 10 is a diagram illustrating a configuration of an image processing apparatus according to a sixth embodiment of the present invention.

Claims (15)

An image processing apparatus for processing an X-ray tomographic image of a subject obtained by X-ray irradiation,
Input means for inputting the X-ray tomographic image recorded on the film as image data,
Extracting means for extracting luminance information at a predetermined position of the input image data, and luminance conversion means for converting a luminance value of the image data based on the extracted luminance information at the predetermined position,
Recognition means for recognizing information about a window level and a window width described on the image data,
An image processing apparatus comprising: a CT value conversion unit configured to convert the luminance-converted image data into a CT value based on the recognized information on the window level and the window width. 2. The image processing apparatus according to claim 1, wherein the input unit is connected to a scanner and can input image data from the scanner. An image processing apparatus for processing an X-ray tomographic image of a subject obtained by X-ray irradiation,
Input means for inputting the X-ray tomographic image recorded as analog data on a video tape as image data,
Extracting means for extracting luminance information at a predetermined position of the input image data, and luminance conversion means for converting a luminance value of the image data based on the extracted luminance information at the predetermined position,
Recognition means for recognizing information about a window level and a window width described on the image data,
An image processing apparatus comprising: a CT value conversion unit configured to convert the luminance-converted image data into a CT value based on the recognized information on the window level and the window width. 4. The image processing apparatus according to claim 3, wherein the input unit is connected to a video tape recorder, inputs an analog video signal from the video tape recorder, and is capable of converting a digital image. The luminance information at the predetermined position is a luminance value of a white portion of a character of a window level or a window width in the image data and a luminance value of a shadow portion thereof,
The brightness conversion unit determines a range in which the brightness value of the white portion is a maximum brightness value and the brightness value of the shadow portion is a minimum brightness value, and normalizes the image data to the range. The image processing apparatus according to claim 1, wherein: The luminance information of the predetermined position is a luminance value of a portion indicating a gray scale in the image data,
4. The image processing apparatus according to claim 1, wherein the luminance conversion unit normalizes the image data using a maximum luminance value and a minimum luminance value of the gray scale. 5. An X-ray CT apparatus comprising the image processing apparatus according to claim 1. An image processing method for processing an X-ray tomographic image of a subject obtained by X-ray irradiation,
An input step for inputting the X-ray tomographic image recorded on the film as image data;
An extraction step of extracting luminance information of a predetermined position of the image data and a luminance conversion step of converting a luminance value of the image data based on the extracted luminance information of the predetermined position,
A recognition step of recognizing information about a window level and a window width described on the image data,
A CT value converting step of converting the brightness-converted image data into a CT value based on the recognized information on the window level and the window width. 9. The image processing method according to claim 8, wherein the input step is connected to a scanner and can input image data from the scanner. An image processing method for processing an X-ray tomographic image of a subject obtained by X-ray irradiation,
An input step for inputting the X-ray tomographic image recorded as analog data on a video tape as image data,
An extraction step of extracting luminance information of a predetermined position of the image data and a luminance conversion step of converting a luminance value of the image data based on the extracted luminance information of the predetermined position,
A recognition step of recognizing information about a window level and a window width described on the image data,
A CT value converting step of converting the brightness-converted image data into a CT value based on the recognized information on the window level and the window width. 11. The image processing method according to claim 10, wherein in the inputting step, a video tape recorder is connected, an analog video signal from the video tape recorder is input, and digital image conversion is possible. The luminance information at the predetermined position is a luminance value of a white portion of a character of a window level or a window width in the image data and a luminance value of a shadow portion thereof,
The brightness conversion step determines a range in which the brightness value of the white portion is a maximum brightness value and the brightness value of the shadow portion is a minimum brightness value, and normalizes the image data to the range. 11. The image processing method according to claim 8, wherein: The luminance information of the predetermined position is a luminance value of a portion indicating a gray scale in the image data,
11. The image processing method according to claim 8, wherein in the luminance conversion step, the image data is normalized using a maximum luminance value and a minimum luminance value of the gray scale. A control program for causing a computer to implement the image processing method according to any one of claims 8 to 13. A storage medium storing a control program for causing a computer to implement the image processing method according to claim 8.

Images