JPH057351A - Picture signal converter - Google Patents

Abstract

(57) [Summary] [Purpose] To make it easier for the actual viewer to see,
Optimally adjust the contrast of a gradational image. [Configuration] At the time of initial setting, a standard image is displayed on an output medium, and an operator sets conversion parameters to suit his or her preference. During normal operation, all original image signals are converted into input signals of the output medium based on the maximum and minimum values of the original image signal in the ROI and the conversion parameters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for optimizing the contrast of an image when displaying (or printing) an image with gradation on an output medium such as a CRT or paper.

[0002]

2. Description of the Related Art X-ray CT, not binary only black and white
(Tomography equipment) and MR (magnetic resonance tomography equipment) images such as images taken in which the middle gradation (shadow) is important, it is difficult to read the image correctly unless the contrast is properly displayed. Becomes If the contrast is not set properly, for example, the gradations of less important parts are expressed finely, while there are inconveniences such as overexposure (halation) and underexposure in the part you really want to read. It is possible that the meaning of the display is meaningless.

In order to avoid such an inconvenience, conventionally, a region of interest (ROI = Region of Interest) is displayed on the screen.
Is provided, and the contrast is adjusted based only on the image data in the inside.

[0004]

The conventional contrast adjustment method when the ROI is set detects the maximum value and the minimum value of the image data in the ROI, and determines the maximum value and the minimum value of the image data of the output medium such as CRT. The data between the both ends was linearly (linearly) converted so that the maximum value and the minimum value were obtained. However, this method considers only maximizing the use of the dynamic range of the output medium within the ROI, and the characteristics of the output medium and a human being (a medical image device of a medical imaging device) who makes some judgment by looking at the image. In some cases, the sensitivity of doctors, etc.) is not taken into consideration. Therefore, the output medium is from CRT to LCD
When replaced with other equipment such as (liquid crystal display), the appearance may change. In addition, a doctor who used to make a diagnosis based on an image taken with a film conventionally used an output medium (CR
When looking at an image displayed on a T or a printout by a laser printer, etc., there is a possibility that the image may feel a little unnatural depending on the imaged site and symptoms.

The present invention has been made in order to solve such a problem, and provides an apparatus for optimally adjusting the contrast of a gradational image so that it is most easy for an actual viewer to see. It is a thing.

[0006]

An image signal conversion apparatus according to the present invention made to solve the above-mentioned problems has an original image signal Sin having gradation as shown in the conceptual configuration of FIG. Of the standard image including the maximum value SMAX and the minimum value SMIN of the original image signal Sin that can be converted into the input signal Sout of the image output medium 14.
Based on the standard image signal generating means 10 for generating d and (b) the display mode of the standard image signal Sstd on the output medium 14, the operator has a parameter of the conversion characteristic from the original image signal Sin to the input signal Sout of the output medium. Initial setting means 11 for setting Pconv, and (c) set conversion parameter Pconv
And a storage means 12 for storing (d) an arbitrary screen area Roi
Value Smax and minimum value Sm of the original image signal Sin within
Based on the maximum / minimum detecting means 15 for detecting in, and (e) the detected maximum / minimum values Smax and Smin and the conversion parameter Pconv stored in the storage means 12, all original image signals Sin are output media. And a conversion means 13 for converting into 14 input signals Sout.

[0007]

In the initial setting, the operator uses the initial setting means 11 while watching the standard image displayed on the output medium 14,
Conversion parameter P so that your own image is the easiest to see
Set conv. This conversion parameter Pconv defines the conversion relationship from the original image signal Sin to the input signal Sout of the output medium 14 for all values between the maximum value SMAX and the minimum value SMIN that the original image signal Sin can take. is there. In addition,
At this time, SMAX is converted into SoutMAX and SMIN is converted into SoutMIN.

In the normal operation, the conversion means 13 outputs all the original image signals Sin based on the parameter Pconv stored in the storage means 12 as follows to the input signal Sou of the output medium 14.
Convert to t. Since the maximum / minimum detecting means 15 takes the maximum value Smax to the minimum value Smin in the region Roi set in a (arbitrary) part of one screen of the entire original image signal Sin, the range is Smax to Smin is generally narrower than the above range SMAX to SMIN. However, the conversion means 13 converts the maximum value Smax and the minimum value Smin in the area Roi into the converted values SoutMAX and SoutM of SMAX and SMIN in the initial setting.
The entire image signal Sin is converted into the output medium 14 so as to be converted into IN.
Input signal Sout. As a result, the image in the region Roi is displayed on the output medium 14 in the same manner as that displayed in the initial setting (that is, in the manner most visible to the operator).

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the image signal converting apparatus according to the present invention is applied to an X-ray TV apparatus will be described with reference to FIGS. The image signal conversion apparatus of this embodiment is used to convert an image signal of a transmitted X-ray image taken by a TV camera into an input signal of CRT. The configuration of the device and the operation during normal operation will be briefly described with reference to FIG. The analog image signal Sin representing the X-ray image from the TV camera (TVC) is first converted into A / D.
It is converted into digital image data (primary image data) for each pixel by the converter 20, and is temporarily stored in the first image memory 21. After the conversion of the image signal Sin of one frame (one screen) is completed, the CPU 24 of the conversion circuit reads out the image data in the first image memory 21 one by one and uses the parameters stored in the parameter memory 27. A predetermined calculation is performed to convert the display image data. The display image data is sequentially stored in the second image memory 22, and is converted into an analog image signal by the D / A converter 23 when the conversion for one screen is completed (even if the A / D conversion is performed simultaneously with the data conversion. Good). The analog image signal Sout is sent as it is to a CRT which is a display device and is displayed.

Before performing such a normal operation, the conversion apparatus must perform initialization and store the conversion parameters in the parameter memory 27. This initial setting process is performed interactively by an operator (for example, a doctor who makes a diagnosis by looking at an X-ray image) using the operation panel 28 while observing the CRT so that the image is in the most visible state for himself. The conversion parameter is predetermined. Details of the initialization process will be described with reference to the flowchart of FIG.

First, in step S10, the CPU 24 reads the image data of the test pattern (standard image) from the test pattern memory 26 and displays it on the CRT. The test pattern here includes the maximum value SMA of the image signal on the input side of the TV camera (as seen from the image signal conversion device) SMA.
An X (maximum luminance) and a minimum value (minimum luminance) SMIN are used (for example, SMPTE). CPU
The maximum value SMAX and the minimum value SMIN of 24 are respectively CR
Linear data conversion is performed so that the T input signal Sout becomes the white level signal SW and the black level signal SB (line 50 in FIG. 5).

However, since the X-ray shadow image displayed on the CRT by such a simple linear conversion is different from the contrast characteristic when the X-ray shadow image is photographed on film, diagnosis is made based on the film shadow image. For a used doctor, it may give the impression of being "tight". In such a case, first, both ends SMAX and SMIN of the conversion line 50 are moved to SMAX2 and SMIN2 by the following formulas, and the width of the output signal (CRT input signal) Sout is slightly compressed (step S11). SMIN2 = SMIN−α · W SMAX2 = SMAX + β · W (where W = SMAX−SMIN.) The parameters α and β in these equations move the maximum / minimum luminance points on the horizontal axis to the outside of what percentage. It is a scale showing whether to do,
When the output medium (CRT in this case) has the characteristic of being easily saturated at the lowest luminance (because it is necessary to increase the output level), the minimum luminance point on the horizontal axis is moved to a lower one ( That is, it is preferable to increase the value of α. By moving the maximum and minimum brightness points on this horizontal axis, input-
The output data conversion line is like line 51.

Next, in order to bring the contrast characteristic of the CRT display closer to the contrast characteristic of the film, the low-luminance portion (lower end portion) R1 is set downward while leaving the central portion Rline of the linear conversion line 51 as a linear conversion region. The convex, high-luminance portion (upper end portion) R2 is deformed so as to have an upward convex curve (step S12), and is deformed so as to have a sigmoid curve as a whole. A quadratic equation, a cubic equation, an exponential function, or the like can be used for the curves at both ends at this time. Although the parameter representing the shape of this curve is simply γ here, it may actually be represented by two or more parameters. Also, change the shape of the curves at both ends,
You may make it represent by each separate parameter.

In this way, the operator determines the conversion characteristic curve 52 so that the operator can easily see it while looking at the test pattern on the CRT screen. The parameters α, β, γ determined by such an initialization process are stored in the parameter memory 27 (step S13).

After the above initialization, the image signal Sin from the TV camera is converted into the input signal Sout of the CRT based on the conversion characteristic curve 52. This process will be described with reference to the flowchart of FIG. First, the analog image signal Sin from the TV camera is converted into digital data by the A / D converter 20 and stored in the first image memory 21 (step S20). When the conversion of the image data of one frame (one screen) is completed, the operator sets a region of interest (ROI) (step S21), and spot noise is removed from the image data in the region (step S22). .. Here, the spot noise is, for example, a point (1
Point) data. of course,
Other definitions may be adopted, or they may be removed at the time of analog image data.

After removing the noise, a histogram of the brightness of the image data in the ROI is created (step S2).
3) The maximum value Smax and the minimum value Smin of the image data in the ROI are detected (step S24). Then, the parameters α, β, γ representing the conversion characteristic curve 52 determined by the initial setting are read from the parameter memory 27 (step S25), and these values (Smax, Smin, α,
.beta., .gamma.), all the original image data in the first image memory 21 is converted into display image data, and the second image memory 22
(Step S26). The data conversion at this time is performed by the maximum value Smax and the minimum value Sm of the image data in the ROI.
Match in with SMAX and SMIN on the horizontal axis of the graph in FIG.
Conversion curve 52 created by parameters α, β, γ
Is used to convert all original image data into output data (display image data) on the vertical axis. Thus, the display image data stored in the second image memory 22 is stored in the D / A converter 23.
Is converted into an analog signal by (step S27), C
Output to RT.

Incidentally, as shown in FIG. 2, when the image is represented by digital data from the beginning like the data from the X-ray CT or the image analysis device, the image data Din is directly converted to the first data. It may be stored in the single image memory 21. Also, the converted image data may be output as it is as the digital data Dout when it is output to a digital display device or when temporarily stored in a storage medium such as a magnetic disk. Further, the conversion curve is not limited to the sigmoid curve as shown in FIG. 5, and may be a curve which is convex upward or convex downward over the entire area. Furthermore, it is also possible to perform histogram equalization (equalization, so that the frequencies of appearance of the respective luminances forming the histogram become equal) from the luminance histogram created in step S23. Further, when the characteristics of the output medium are already known, the optimum conversion table can be determined in accordance with the characteristics.

[0018]

In the image signal converting apparatus according to the present invention, the conversion parameter is set in advance so that the operator can display the display mode most easily for him / herself, and the image signal is output medium based on the conversion parameter in the normal operation. Since it is converted into the signal of, the gradational image is always displayed on the output medium with the optimum contrast. The output medium here includes a laser printer and the like in addition to the CRT and LCD.

[Brief description of drawings]

FIG. 1 is a block diagram conceptually showing an example of the configuration of the present invention.

FIG. 2 is a block diagram showing the configuration of an image signal conversion apparatus for X-ray TV that is an embodiment of the present invention.

FIG. 3 is a flowchart showing an operation at the time of initial setting of the image signal conversion apparatus according to the embodiment.

FIG. 4 is a flowchart showing an operation during normal operation of the image signal conversion apparatus according to the embodiment.

FIG. 5 is a graph showing an example of an image signal conversion characteristic curve.

[Explanation of symbols]

10 ... Standard image signal generating means 11 ... Initial setting means 12 ... Storage means 13 ... Conversion means 14 ... Image output medium 15 ... Maximum / minimum detection means 20 ... A / D converter 21 ... First image memory 22 ... Second image Memory 23 ... D / A converter 24 ... Image signal converter CPU 26 ... Test pattern memory 27 ... Parameter memory 28 ... Operation panel 52 ... Conversion characteristic curve Rline ... Linear conversion area R1, R2 ... Non-linear conversion area ROI ... Region of interest Smax, Smin ... Maximum / minimum value in ROI SMAX, SMIN ... Maximum / minimum value in all screens

Claims (1)

Claim: What is claimed is: 1. An apparatus for converting an original image signal having gradation into an input signal of an image output medium, the original image of a standard image including maximum and minimum values that the original image signal can take. Standard image signal generating means for generating an image signal, and an initial setting for the operator to set the parameter of the conversion characteristic from the original image signal to the input signal of the output medium based on the display mode of the standard image signal on the output medium. Means, storage means for storing the set conversion parameters, maximum / minimum detection means for detecting maximum and minimum values of the original image signal in an arbitrary screen area, detected maximum / minimum values and storage means An image signal conversion device, comprising: a conversion unit that converts all original image signals into input signals of an output medium based on the conversion parameters stored in.