JPH0581110B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a gradation setting method in an image processing device such as a medical image processing device that digitally processes an X-ray photograph or a printing layout system, and is particularly applicable to reading continuous tone images such as photographs. This invention relates to a gradation setting method when outputting a photographic image after processing it into a digital signal. [Background of the Invention] Thanks to the rapid development of computers and semiconductor technology, it has become natural for image processing devices that handle continuous tone images such as photographs to perform digital processing. FIG. 1 shows a block diagram of an image processing system used for medical purposes. One image processing device A is
This device is mainly responsible for image input, output, storage, etc., and the other image processing device B mainly uses and processes image data stored in image processing device A, converting it into diagnostically effective image data. It is a processing device. The image processing apparatus A converts an X-ray film 10 generated in a hospital into digital data using a film digitizer 2 as an image input means, and then sends it to an image processing section 3 as an image processing means, and then sends it to an image processing section 3 as an image processing means.
to be memorized. The image processing unit 3 is an image processing device B.
In response to the image data request from the image storage unit 7, the image communication unit 8, 8' searches for necessary image data.
, or to store image data sent from another image processing device in the image storage section 7 again, or to output the raw image data using the film printer 4 as an image output means. A process of scanning and exposing the film is performed. The film that has been scanned and exposed is processed by a developing machine 5 to be converted into a hard copy, and becomes a hard copy film 11. Here, as a basic characteristic of the image processing apparatus A, if the input image data is converted into a hard copy without any processing, the output hard copy film 11 will be exactly the same as the original X-ray film 10. desirable. However, since the gradation characteristics of hard copy film are non-linear, it is actually necessary to perform gradation conversion of image data, and this gradation conversion characteristic is usually set as follows. Using a known number of levels of data values, a test chart is created by exposing and developing the film in a pattern. Measure the density of the data pattern at each density level with a densitometer, and plot the data values and measured densities on a graph (plots a1 and a in Figure 8).
2, a3,..., a14). In order to obtain a continuous tone conversion characteristic curve,
The data obtained is interpolated and smoothed (curve a in Figure 8). Data y for obtaining an ideal gradation characteristic (curve b in FIG. 8) for gradation data x is obtained from a graph, and a correspondence (x, y) is taken. Find y for all the gradation data x and use this as gradation conversion data. However, the gradation characteristics of the film change depending on the lot, type, development conditions, etc., so when these change, it is necessary to change the gradation conversion characteristic curve each time. It was a heavy burden for the operator to perform this manually. Therefore, in a system in which the film digitizer 2 and the film printer 4 are connected online as shown in FIG. It is proposed to save labor. Here, a film digitizer 2 is used instead of a densitometer, and interpolation and smoothing processing are automatically performed by an image processing section 3 inside the image processing apparatus A. However, in the above method, since the test chart is automatically converted into digital values by the film digitizer 2, the positional relationship between the density pattern of each level on the created test chart and the pattern of the read image data is not correct. If it doesn't match exactly, we can't take action. Therefore, first of all, in order to clarify these positional relationships, it is necessary to strictly define the arrangement and size of the density patterns of the image data for the test chart. Second, when reading the test chart film with the film digitizer 2, it is necessary to avoid setting the test chart film in the film digitizer 2 in the wrong position and orientation. However, even with these considerations, errors in the reading position by the film digitizer 2, errors in the recording position of the test chart by the film printer 4, and deviations in the setting position when setting the test chart film in the film digitizer 2, etc.
Accurate alignment is not possible. Therefore, it was necessary to increase the size of each density pattern in the test chart to reduce the influence of positional fluctuations. Therefore, the number of density patterns is limited, and in order to create a smooth gradation conversion table, interpolation of each data and its smoothing are essential. Furthermore, when a plane scanning printer such as a CRT imager or laser printer is used as the film printer 4, there is a problem in that positional exposure changes occur on the film surface, causing subtle density distortions in the test chart. It was hot. This is largely due to positional reflectance fluctuations of the reflective mirror used in the film printer 4 and the shading effect of the imaging lens, and therefore, such density distortion is not present in the test chart. An accurate gradation conversion table could not be obtained unless it was measured in advance and the data read by the film digitizer 2 was corrected. In the conventional method, such density distortion is alleviated by taking an average within the density pattern, but although this method is effective against distortion within the density pattern, it also reduces the gradual distortion between patterns. It has no effect on distortion at all. The density distortions that depend on the film printer 4 and the developing device 5 often include such gentle distortions, and in this sense too, the conventional methods have had problems. Therefore, we obtained the frequency distribution of each density level on the created test chart and the frequency distribution of each density level of the read image data, and created a gradation conversion table to make these two frequency distributions correspond. This is proposed in, for example, Japanese Patent Laid-Open No. 58-68040. However, since both frequency distributions obtained here each have curved characteristics, it is difficult to establish a correspondence relationship between the two, and it is difficult to create a gradation conversion table. [Object of the Invention] The present invention has been made in view of the above points, and its object is to easily match the two frequency distributions described above, and to create a gradation conversion table. An object of the present invention is to provide a gradation setting method that facilitates the creation of gradations. [Structure of the Invention] For this purpose, the present invention provides an image input means for photoelectrically converting an image and inputting it as digital data, an image processing means for processing digitized image data from the image input means, and an image processing means for processing the image data. In an image processing apparatus equipped with an image output means for hard copying digital image data from the means, a test chart is created by the image output means using first image data whose frequency distribution is known for each density level, The test chart is converted into second image data by the image input means, and the frequency distribution for each density level of the second image data is determined by the image processing means, and then the frequency of the first image data is determined by the image processing means. A gradation setting method for creating a gradation conversion table for image data such that the distribution corresponds to the frequency distribution of the second image data, wherein the test chart is created using uniform random numbers. One image data was generated, and the frequency distribution of each density level of the first image data was made uniform. [Examples] Examples of the present invention will be described below. Second
The figure shows a film digitizer 20 of one embodiment. The laser beam emitted from the laser light source 21 has its optical path changed by a mirror, is shaped into an appropriate beam shape and beam diameter by a beam shaping lens 22, is deflected in one direction by a rotating polygon mirror 23, and is transmitted to an fθ lens 24. X by a so-called imaging lens
The beam is converged to a narrow beam diameter on 10 surfaces of the line film,
scanned. The laser light that has reached the X-ray film 10 is absorbed and scattered by the X-ray film 10 and is attenuated, but the laser light that has passed therethrough is guided to a photomultiplier 26 by a convergent 25 composed of a fiber bundle. . This photomultiplier 26 converts the guided laser light into a corresponding electrical signal. Since the level of this electrical signal corresponds to the transmittance of the X-ray film 10, it is input to a logarithmic converter 27 in order to convert it into density, and the time series output signal of this logarithmic converter 27 is converted into density values on the scanning line. A corresponding signal will be generated. The output signal of the logarithmic converter 27 is distorted due to the shading effect of the fθ lens 24, so it passes through the shading correction circuit 28 and is converted into a signal without shading, and then is converted into a digital value by the A/D converter 29. be done. The film 10 is controlled to move by one scanning line per scanning period in a direction substantially perpendicular to the scanning line, and by sequentially performing this operation, the density information on the X-ray film 10 is changed in time series. It is converted into a digital data string and output. The film digitizer 20 according to this embodiment has an image diameter of 120 μm on the film surface of the laser beam, a pixel size of 175 μm x 175 μm, a density gradation level of 1024 gradations (10 bits), and a readable film. The maximum width is 14 inches, and the readable density range is 0 to 3.5. FIG. 3 is a diagram showing a film printer 40 used in this embodiment. Here, components that perform the same functions as those used in the film digitizer 20 are given the same reference numerals with a dash (') added thereto.
Digital image data inputted from an image processing section 30, which will be described later, is converted by a gradation conversion table RAM 41 and stored in a buffer memory 42.
The data in the buffer memory 42 is sequentially read out in synchronization with the deflection of the laser beam by the rotating polygon mirror 23', converted into an analog signal by the D/A converter 43, and then current amplified by the amplifier 44, and then modulated by AM. The signal is modulated by the modulator 45 and input to the AOM 46.
This AOM 46 is a modulator that modulates the intensity of the laser beam using a modulation signal, and the laser beam intensity-modulated here is deflected by the rotating polygon mirror 23' and fθ
The lens 24 allows the raw printer film 11'
Converges and forms an image on the surface. As a result, film 1
1' is scanned and exposed. The film 11' is moved in a direction substantially perpendicular to the scanning line in the same way as the film 10 in the film digitizer 20.
As a result, the entire surface of the film is exposed. In the film printer 40 of this embodiment, the image diameter of the laser beam on the film 11' surface is 70 μm, the pixel size is 87.5 μm×87.5 μm, and the density gradation level is 70 μm.
It has 1024 gradations (10 bits), and the recordable film size is fixed at 8 inches x 10 inches.
The maximum number of recordable pixels is 2200 x 2800, and the recording density is 0.
The specification is to reproduce the range of ~3. In addition, the RAM 41 for the gradation conversion table has input data.
It is 10 bits and controls the brightness modulation level of the laser beam.
Since it is set to 4096 levels, it has a 1024 x 12 bit configuration. The data in this RAM 41 can be changed under control from the image processing section 3. FIG. 4 is a diagram showing an example of the image processing section 30 of this embodiment. The image processing unit 30 performs various processes on image data, but only the configuration necessary for this embodiment is shown here. The image input control section 33 synchronizes with the film digitizer 20 under the control of the processing control section 31.
The image data read by the film digitizer 20 is sequentially received and sent to the image data bus 37. The image memory 34 is for temporarily storing image data read by the film digitizer 20, and can store 2048×2560 pixels and 10 bit data. Frequency accumulator 35
is for accumulating the pixel frequency of 10-bit data in the image memory 34, and internally contains 1024 pixel frequencies.
A 24-bit frequency memory and a 24-bit adder are built-in. Then, under the control of the processing control unit 31, a necessary portion of image data is received from the 2048×2560 pixel image memory, and the content of the address of the frequency memory indicated by the value of the image data is incremented by 1. The image output control section 36 synchronizes with the film printer 40 under the control of the processing control section 31 and transmits the data in the image memory 34 to the film printer 40. The processing control unit 31
It is mainly configured with a CPU, and in addition to controlling the entire image processing section 30, it also has a test chart image data generation function, a function to normalize the frequency of image data accumulated by the frequency accumulator 35, and gradation conversion. It has table creation functions, etc. The gradation conversion table setting algorithm described here is one of the utility packages in this image processing device, and is managed in parallel with the actual routine processing functions and the like under the OS. The data memory 32 is for storing normalized frequency distribution table data, gradation conversion table data, and the like. Next, the test chart image generation function will be described. In the test chart used in this example, one density pattern is printed on the film printer 40.
It has 32 x 32 pixels, which is actually a 2.8 mm x 2.8 mm square, and this pattern consists of 64 x 80 pixels, a total of 5125 pieces. Therefore, the test chart pattern itself has a size of approximately 179 mm x 224 mm.
The film 11' for recording the test chart is 8
inch x 10 inch (approx. 200 mm
(equivalent to mm), ID information of this image, recording time,
Because it is necessary to record character data such as the name of the test chart creator, the test chart pattern is
Recorded centered at the top of the character. Although 5,120 pieces of density pattern image data are required, in this embodiment, as shown in Table 1, 64 pieces of data are made to appear with approximately equal frequency.
They are placed randomly. The data in Table 1 is selected so that the portions with smaller numbers (corresponding to the lower recording density of the film printer 40) are denser. This is because, among film densities, the lower the density, the higher the human discrimination ability, and the reproducibility of the film is strictly required. Further, the reason why they are arranged randomly is to average out the influence of density distortion at the recording position.

〔Effect of the invention〕

As described above, according to the present invention, a test chart is created by generating first image data using uniform random numbers, and the frequency distribution of each density level of the first image data is made uniform. Therefore, the frequency distribution table of the first image data has a linear characteristic. Therefore, comparison with the frequency distribution table obtained from the second image data becomes easy, and it becomes easy to create a gradation conversion table from both frequency distribution characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a medical image processing system, Fig. 2 is a block diagram of a film digitizer of this embodiment, Fig. 3 is a block diagram of a film printer of this embodiment, and Fig. 4 is an image of an image of this embodiment. Block diagram of the processing unit,
FIG. 5 is a flowchart for setting density pattern data in this embodiment, FIG. 6 is a flowchart in another embodiment, FIG. 7 is a flowchart in yet another embodiment, and FIG. 8 is a gradation conversion flowchart. The characteristic diagrams in FIGS. 9a to 9c are frequency distribution conversion characteristic diagrams, and FIGS. 10a and 10b are characteristic diagrams of a cumulative frequency distribution table.

Claims (1)

[Scope of Claims] 1. Image input means for photoelectrically converting an image and inputting it as digital data, image processing means for processing digitized image data from the image input means, and digital image from the image processing means. In an image processing apparatus equipped with an image output means for hard copying data, a test chart is created by the image output means using first image data whose frequency distribution for each density level is known, and the test chart is After converting the second image data into second image data by the image input means and determining the frequency distribution for each density level of the second image data by the image processing means, the frequency distribution of the first image data and the second image data are converted into second image data. A gradation setting method for creating a gradation conversion table of image data so as to correspond to a frequency distribution of image data, the method includes creating a gradation conversion table of image data such that the frequency distribution of the first image data corresponds to the frequency distribution of the first image data using uniform random numbers. A gradation setting method characterized in that the frequency distribution for each density level of the first image data is uniform. 2. The gradation setting according to claim 1, wherein the size of the density pattern corresponding to each density level of the test chart is from 2 times to 100 times the aperture diameter of the image input means. Method. 3 The density level of the data having the first image roughness is approximately 1/1/1 of the number of quantization levels of the image input means.
The gradation setting method according to claim 1 or 2, characterized in that the number is 20 or more.