JPS63258166A - Noise detection method for picture signal - Google Patents

Abstract

PURPOSE:To accurately detect noise components by comparing the value of the picture signal (a) of an attended picture element A with the average value (m) of the respective picture signals of the plural picture elements in the vicinity of the picture element A. CONSTITUTION:A read picture signal S is digitized by an A/D converter 21 and inputted to a noise elimination circuit 22. In the circuit 22, the picture signal (a) of an attended picture element A and the respective signals of the ten pieces of picture elements neighboring said picture element A in the main scanning direction are extracted, the average value (m) and the variance sigmaare obtained, then the value of ((m)+3sigma) and that of the picture signal (a) are compared. In case (a)>(m)+3sigma, noise components are considered to be included in the picture signal (a). In such a way, a black dot can be prevented from occurring in a reproduced picture.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for detecting noise components contained in an image signal obtained by reading radiation image information stored and recorded on a stimulable phosphor sheet. It is.゛(Prior art) When radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet #i, etc.) is irradiated onto a light source at a certain mountain pass, part of the ()Ja energy becomes fluorescent. Tr is accumulated in the body, and this phosphor is illuminated with excitation light such as visible light f) J? It is known that the phosphor exhibits stimulated luminescence depending on the N-product energy, and a phosphor exhibiting this property is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, you can photograph subjects such as the human body! 1
) Jls/image information is once recorded on a sheet of stimulable phosphor, the stimulable phosphor sheet is irradiated with excitation light to generate stimulated luminescence, and the stimulated luminescence is detected by a photodetector. Radiographic image information recording and reproduction that reads the image signal in a charging manner to obtain an image signal, and outputs the image of the subject as a visible image on a recording 4411 of a photographic photosensitive material, etc., and on a display device such as a CRT based on this image O signal. A system has already been proposed by the applicant. (Unexamined Japanese Patent Publication No. 55-12429, 5
0-11395@ etc. ) The above-mentioned stimulable phosphor sheet is disclosed in, for example, Japanese Patent Application Laid-open Nos. 56-11392 and 5B-1259.
As shown in No. 9, by emitting the radiation energy that remains after reading the radiation image information by irradiating it with light or heat, it can be used repeatedly.

(Problem to be solved by the invention) However, since this stimulable phosphor sheet has a very high concentration, a trace amount of 221 R is mixed into the phosphor itself.
The energy of environmental radiation such as radiation emitted from radioactive isotopes such as B and 40, or cosmic rays and hk radiation emitted from radioactive isotopes contained in paint on indoor walls, etc., also accumulates. .

When recording and reproducing the above-mentioned radiant (g) J-ray image information using a stimulable phosphor sheet that has accumulated such radiant ()Js energy, small sunspots may appear in the reproduced image due to the above-mentioned radiant (g)1e energy. occurs. Such black spots naturally impair the quality of the reproduced image.

If it is possible to detect the noise component that causes black spots as described above from the image signal obtained by the above-mentioned radiation image information reading process, the reproduced copper wire image can be generated by applying various processes to the image signal to remove this noise component. It is possible to prevent the occurrence of sunspots.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that can accurately detect the noise component from an image signal obtained by reading an M'm phosphor sheet.

(Means for Solving the Problems) The method for detecting noise in an image signal according to the present invention is based on the image @ signal a for each pixel of interest A obtained by the above-mentioned radiation image information reading process, and the pixel of interest A31i. Find the average value m for each image signal S, b,, b3...bn for a plurality of neighboring images ^Bt, Bz, 83...8n, and a>m+k [If k is a constant 1, the image fQ ja is considered to contain noise.

Note that the above average value m is the image signal a.

The average value or median value of bl, b, , b3...bn can be used.

(Function) According to the research conducted by the present inventors, the radiation energy that accumulates in the stimulable phosphor sheet as described above and becomes a noise component is due to the surrounding Q445a energy, that is, the correct radiation (g) J-ray image. h! It has been found that it has a uniquely high energy compared to the iQ4 ray energy, and that in images commonly used for diagnosis, it usually accumulates within a range of about 9 stone's worth, and is particularly concentrated in a range of about 1 or 2 pixels. Ta. On the other hand, image signals for pixels that are close to each other have a fairly high correlation, as is well known. Therefore, if the value of the constant is appropriately determined, when the image signal J8a does not contain the above-mentioned noise component, a<m+, whereas when the image signal a contains the above-mentioned noise component, If a high value is taken, a>m+, so the presence or absence of the noise component can be detected based on such a comparison.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a radiographic image information reader "jAe1" in which noise detection is performed by the method of the present invention.

For example, by irradiating radiation such as Xa that has passed through the subject, the number of transmitted images Q4f15i1 image information of the subject can be '
The stimulable phosphor sheet 10 on which the fr product was recorded.

A sheet conveying means 11 such as an endless belt conveys the sheet in the direction of arrow Y for sub-scanning with the excitation light.

Further, the laser beam 13 as excitation light emitted from the laser light source 12 is directed to an optical deflector 1 such as a galvanometer mirror.
4), and the stimulable phosphor sheet 10 is main-scanned in the direction of arrow X, which is substantially perpendicular to the sub-scanning direction Y. Stimulated luminescent light 15 is emitted from the portion of the sheet 10 irradiated with the laser beam 13 in an amount corresponding to the radiation image information stored and recorded, and this stimulated luminescent light 15 is collected by the condenser 16. The light is emitted and is photoelectrically detected by a photomultiplier (photomultiplier tube) 17 as a photodetector.

The light collector 16 is formed by molding a light-guiding material such as an acrylic plate, and has a linear incident end surface 16a. ! An emission end surface 16 is arranged to extend along the beam scanning line on the off-board phosphor sheet 10 and is formed in an annular shape.
The light receiving surface of the photomultiplier 17 is coupled to b. The stimulated luminescent light 15 that enters the light condenser 16 from the incident end surface 16a travels through the interior of the light condenser 16 through repeated total reflection, and exits from the output IA'4 end 16b.
The photomultiplier t1-17 detects the amount of stimulated luminescent light 15 that carries the radiation image information and is received by the photomultiplier 17.

The analog output signal of the photomultiplier 17 is logarithmically converted and amplified in the log amplifier 20, and is converted into a read image signal f that carries the light output of the stimulated luminescent light 15, that is, radiographic image information.
The signal 88 is input to the A/D converter 21. The read image signal S is digitized by this A/D converter 21. The digital read image signal Sd obtained in this way is then subjected to processing to be described later in the noise removal circuit 22 to become a converted signal Sd', and is subjected to image processing such as gradation processing in the image processing device 123, and is then subjected to image processing such as gradation processing, etc. The image is input to an image reproducing device 24 such as a CRT or an optical scanning recording device, and the radiation image stored and recorded by the stimulable phosphor sheet 10 is reproduced in the uniform reproducing device 24.

As mentioned above, the stimulable phosphor sheet 10 is exposed to radiation emitted by radioactive isotopes in the phosphor,
Energy from environmental radiation in A-kasa may accumulate. When this stimulable phosphor sheet 10 is subjected to radiation image information reading as described above, the read image signal S contains noise components due to this radiation energy, and is reproduced by the image reproducing device 24. Image 30
As shown in FIG. 2, a small black spot N appears. The noise removal circuit 22 is provided to prevent the occurrence of such black dots N. The processing by this noise removal circuit 22 will be explained in detail below.

A noise removal circuit 22 consisting of a microprocessor, etc.
Upon receiving the digital image signal @3d carrying the images, the image signal a for each image of interest JA among the signals Sd, -
As an example, 10 pixels adjacent in the main scanning direction with this pixel of interest A sandwiched in the center are as, °Bz, 83.8
4.85 M Bs , Bv sBe , B! l,B
+・ Each image signal P7E) l − (see Figure 3)
b2- bm, bas b5s blit by.

b day, b! I, bI@ are extracted, the average value m and variance σ of these 11 gJ signals aat and ~b are determined, and then the value of (m+3σ) and the value of the image signal a are compared. If a>m+3σ, it is assumed that the image signal a contains the above-mentioned noise component, and the signal a is converted into, for example, image 4g b1 of 109.
Convert to the minimum value, maximum value, average value, median value, etc. of ~bIe.

As mentioned above, if the image signal l+a does not include the noise component, a<m+k (=3σ in this example), but if the image signal l+a contains the noise component, the value of It is uniquely higher than the image signals b1 to b1- of ~BI@.Therefore, as mentioned above, the image signals @a and (m+
3σ), it is possible to accurately detect whether or not the image signal a contains a noise component.

If it is determined that a noise component is included, by converting the image signal a as described above, the noise component due to environmental radiation or the like is approximately removed. Therefore, if both radiation edges are reproduced based on the image signal @3d' which has been subjected to the above processing in the noise removal circuit 22, the above-mentioned black spot N can be prevented from occurring in the reproduced image.

In the above embodiment, the value of the constant set to 3σ is based on the size of the black spot N, that is, the stimulable phosphor sheet 10.
The accumulation size of the environment number tAIa# above.

Other suitable degrees unrelated to the variance σ are calculated based on the distribution state of the normal image equi-arch for pixels that are close to each other.
May be set to a value. Also above 1111! Instead of the average value m of the uniform signals a, b1 to bl of I, their median value or the like may be used. In addition, the converted value of the image signal a when it is considered to contain a noise component is the minimum value, average value, etc. of the image signal bi xb as described above, and is also generated based on the average value m and variance σ. It may also be a random value etc.

Furthermore, in the above embodiment, it is checked whether or not the image signal a of pixel A contains a noise component, but at the same time, it is checked whether the image signal of the neighboring pixels of pixel A similarly contains a noise component. It is also possible to detect the size of the black spot N (in other words, the size of the black spot N). That is, the explanation will be based on the above embodiment.

a>m+3σ... Check whether or not (1) holds, and for example, >m+2
σ...(2 bl>m+2σ...(3) b3>m+σ...(4) b,>m+σ...(5) Does it hold true? For example, (1), (
If both of the two equations or both of equations (1) and (3) are satisfied, the black point size is considered to be two pixels, and the image signal b1 or bl is converted together with the uniformity signal a as described above. Note that the converted value of the image signal bl or s may be equal to or different from the converted value of one image signal a (the same applies hereinafter). Also (1), (2), (
If both of the three equations hold true, it is assumed that the black point size is three pixels, and the image signals b1 and b are converted together with the image signal a.

Similarly, (1), +2), +31 equations and (4)
Alternatively, if formula (5) holds true, the black point size can be considered to be 4 pixels, and (1), (2), +31, (4
1. (If all formulas 51 are satisfied, the black point size can be considered to be 5 pixels, so the image signal can be converted according to the size.

In addition, when performing as described above, pixel A is set to 1.
As the pixels are shifted, the image 1 of one pixel
No. 3 will undergo up to 5 conversions and become C, so
Each converted value may be stored in a memory, and the maximum value, minimum value, average value, median value, etc. of these converted values may be used as the final converted value. Further, in this case, the image signal a of each pixel A may be deemed to have noise in some cases and may be deemed to have no noise in some cases in the noise detection processing performed five times. In order to deal with this, for example, only when the image signal a of each pixel of interest A is determined to be noise-free in all five noise detection processes, the signal value for that pixel A is finally determined. The original signal a may be left as it is, and if it is determined that there is noise even in the other round, the above conversion process may be performed.

Above, an embodiment has been described in which image signals are extracted for the pixel of interest A1 and the neighboring pixels 81 to Bu arranged in a one-dimensional direction with the pixel A.
It is also possible to extract each uniform signal of a plurality of pixels extending two-dimensionally in the vicinity of , and perform noise detection based on their average value. That is, in that case, consider a pixel of interest A and 24 neighboring pixels 81 to B24 surrounding this pixel of interest A, as shown in FIG. 4, for example.

And uniformity signal b1 regarding these neighboring pixels 81 to B
For example, the average value m of ~b24 is calculated, and if the uniformity signal a regarding the pixel of interest A is a>m+k, it is assumed that the image signal a contains a noise component. In that case, the matching signal a is the minimum value, maximum value, average value, median value,
Or pixels B T ~B adjacent to the pixel of interest A
! ,B,2. , B +3 and B1, ~B, may be converted into the minimum value, maximum value, average value, median value, etc. of a. The above processing is performed for each pixel by shifting the pixel of interest one pixel at a time.

Also in this case, as described above, it is checked whether or not the image signal a of the pixel of interest A contains a noise component, and the adjacent pixels B7 to Bas, B8. It is also possible to check whether or not noise components are included in the image signals of and Bag to B, &, and if it is determined that there are noise components, those image signals may be converted to appropriate values.

(Effects of the Invention) As explained in detail above, according to the noise detection method of the present invention, the radiation emitted by the radioactive isotope in the stimulable phosphor is
Even if energy from radiation or environmental radiation accumulates on the stimulable phosphor sheet, the noise component in the read image signal can be accurately detected, thereby making it possible to accurately remove this noise component.

As a result, it is possible to prevent the aforementioned black spots from occurring in the reproduced radiation image, thereby improving the image quality of the reproduced radiation S image and greatly improving its diagnostic performance.

In addition, there is no need to pay much attention to the management of stimulable phosphor sheets to avoid the accumulation of radiation energy that can become a noise source, so institutions that handle many stimulable phosphor sheets, such as large hospitals, are Management of phosphor sheets is facilitated.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a radiographic information reading device equipped with means for detecting noise according to the method of the present invention, and FIG. 2 is a schematic diagram showing an example of a reproduced radiographic image in which black spots appear according to the present invention. 3 is a schematic diagram showing an example of a pixel of interest and its neighboring pixels according to the method of the present invention, and FIG. 4 is a schematic diagram showing another example of a pixel of interest and its neighboring pixels according to the method of the present invention. 10... Stimulable phosphor sheet 11... Sheet conveyance means 12... Laser light source 1
3... Laser beam 14... Optical deflector 15.
・・Photostimulant luminescence light

Claims (4)

[Claims] (1) A stimulable phosphor sheet on which radiation image information is accumulated and recorded is irradiated with excitation light, and the stimulated luminescent light generated from the part of the sheet irradiated with this excitation light is photoelectrically detected by a photodetector. A method of detecting noise contained in an image signal carrying the radiographic image information obtained by reading the image signal a for each pixel of interest A and a plurality of pixels B_1 and B_2 near the pixel of interest A. , B_3...B_n
Each image signal b_1, b_2, b_3...b_
A method for detecting noise in an image signal, characterized in that an average value m with respect to n is determined, and if a>m+k [k is a constant], it is considered that the image signal a contains noise. (2) As the average value m, image signals a and b_
1, b_2, b_3, . . . b_n. 1, b_2, b_3, . . . (3) As the average value m, image signals a and b_
1, b_2, b_3, . . . b_n. (4) The constant k is the image signal b_1, b_2, b_3...
. . . The method for detecting noise in an image signal according to any one of claims 1 to 3, wherein the variance σ of b_n is α times (α is a constant).