Electronic endoscope system

Abstract

Electronic endoscope system (10), comprising: - a video observation part (11); - an illumination device (21, 26, 31, 34) which emits standard light or excitation light from the video observation part (11) onto an object, wherein the standard light is reflected by the object and the excitation light brings the object into an excited state in which the object emits fluorescent radiation; - an imaging device (14) arranged in the video observation part (11) and receiving the reflected standard light and the fluorescent radiation to record a standard image (71) or a fluorescent image (72); - an image synthesis processor (56) that combines the standard image (71) and the fluorescent image (72) into a synthetic image (74) such that a color signal of the synthetic image (74) is equal to a color signal of the standard image (71) and a luminance signal of the synthetic image (74) is a mixture of a luminance signal of the standard image (71) and a luminance signal of the fluorescent image (72) in a predetermined ratio; and an adjustment processor (54) that adjusts the gain of the luminance signal of the standard image (71) and / or the fluorescent image (72).

Description

[0001] The invention relates to an electronic endoscope system capable of identifying abnormal tissue such as cancer in an organ based on autofluorescence or self-fluorescence radiation emitted by tissue illuminated with excitation light.

[0002] Tissue in an organ illuminated with excitation light of a wavelength in or near the ultraviolet range enters an excited state, causing it to emit autofluorescence radiation. The intensity of autofluorescence radiation emitted by abnormal tissue, such as cancer, is weaker than that emitted by normal tissue. Autofluorescence endoscope systems are known from the prior art, which identify abnormal tissue based on an autofluorescence image generated from autofluorescence radiation.

[0003] However, a lumen, i.e., an internal hollow space, present in an organ does not emit autofluorescence radiation, so the intensity of autofluorescence radiation in this lumen is weak, similar to that in abnormal tissue. It is therefore not possible to distinguish abnormal tissue from the lumen based on the autofluorescence image alone.

[0004] In the autofluorescence endoscope system, the normal or standard image obtained when the tissue is illuminated with white light is also taken into account to identify abnormal tissue.

[0005] The lumen is dark in the standard image because it does not reflect white light, while the abnormal tissue is bright in the standard image because it reflects white light. Therefore, the part that is dark in the fluorescence image but bright in the standard image is identified as abnormal tissue.

[0006] Typically, the standard image and the fluorescence image are arranged side by side on the same monitor, allowing the operator to visually identify abnormal tissue based on these two images displayed simultaneously on the monitor. However, it is difficult to identify abnormal tissue using this method because the image display area for each image is comparatively small. Furthermore, the success of this method for identifying abnormal tissue depends on the intuition and experience of the attending physician. Therefore, there is a concern that a physician with insufficient experience may not be able to reliably identify abnormal tissue.

[0007] For this reason, improved autofluorescence endoscope systems have recently been developed, which are described below. For example, Japanese Patent Publication 2003-290130 proposes automatically identifying abnormal tissue based on both the luminance values ​​of the standard image and the luminance values ​​of the fluorescence image, and superimposing a false color, such as yellow or red, over the area corresponding to the abnormal tissue. This method makes it easy to identify abnormal tissue, even if the attending physician has little experience.

[0008] However, this method does not allow viewing the tissue itself, which corresponds to the area over which the sham color is superimposed. Furthermore, there is the problem that if a portion of the tissue is bleeding, this bleeding portion is mistakenly identified as abnormal tissue, so the sham color is superimposed over the bleeding portion. Similar to abnormal tissue, the luminance value of the bleeding portion may be small in the fluorescence image but large in the standard image.

[0009] Japanese Patent Publication 2003-126014 discloses generating fluorescent image signals corresponding to the fluorescent image by illuminating the tissue with excitation light and acquiring two types of standard image signals generated when the tissue is illuminated with light of different colors. A pseudo-color image is generated from the two types of standard image signals and the fluorescent image signals, respectively, to identify normal tissue using the first pseudo-color and abnormal tissue using the second pseudo-color. However, the pseudo-color image does not express the tissue in its natural color, making tissue observation difficult.

[0010] US Pat. No. 6,692,429 B1 discloses an electronic endoscope system that generates a standard image when illuminated with white light and a fluorescence image when illuminated with excitation light, which are combined to form a synthesized image. This system is designed to suppress the interfering influence of autofluorescence radiation in the fluorescence image. The amplification factor of an image capture device is adjusted so that the fluorescent light, cleansed of the interfering autofluorescence radiation, exhibits a greater amplification than the white light reflected from the object.

[0011] WO 2005 034 747 A1 discloses a medical imaging system in which a fluorescence image is superimposed on a standard image to create a synthesis image. The opacity of the image overlay is adjustable.

[0012] US 6 473 637 B1 also describes an endoscope system in which a synthesis image is composed of a fluorescence image and a standard image.

[0013] The object of the invention is to provide an electronic endoscope system which is capable of displaying abnormal tissue which is distinguishable from normal tissue without using a colour which is different from the natural tissue colour.

[0014] The invention solves this problem by the subject matter of claim 1. Advantageous further developments are specified in the subclaims.

[0015] The invention is explained in more detail below with reference to the figures, in which: Fig. 1 a block diagram of an electronic endoscope system; Fig. 2 a schematic representation of a rotatable aperture; Fig. 3 a schematic representation of a standard image displayed by a monitor; Fig. 4 is a schematic representation of a fluorescence image displayed on a monitor; Fig. 5 is a schematic representation of a double image displayed on a monitor; Fig. 6 is a schematic representation of a synthesis image displayed on a monitor; Fig. 7 is a timing chart showing the method of generating image signals in an imaging device; Fig. 8 is a circuit diagram showing the image processing block; and Fig. 9 is a timing diagram showing the method for generating dummy frames for five frame periods. Description of preferred embodiments

[0016] The invention is described below using exemplary embodiments with reference to the figures.

[0017] Fig. 1 is a block diagram of an electronic endoscope system 10. The electronic endoscope system 10 has an image or video processor 20, a video observation part (videoscope) 11, and a monitor 46. The video observation part 11 and the monitor 46 are connected to the video processor 20.

[0018] The video observation part 11, which is inserted into the human body to observe tissue in an organ, can be attached to and detached from the video processor 20. The video observation part 11 has a diverging lens 12, an objective lens 13, a light guide 15, an excitation light blocking filter 19, and an imaging device 14. The diverging lens 12 and the objective lens 13 are arranged at the distal end portion, designated 11a, of the video observation part 11. The excitation light blocking filter 19 and the imaging device 14 are arranged in this order behind the objective lens 13 on its optical axis. The light guide 15 is inserted into the video observation part 11. The exit end of the light guide 15, designated 15A, is arranged behind the diverging lens on its optical axis, while the entrance end of the light guide 15, designated 15B, is located in the video processor 20.

[0019] The video processor 20 has a time controller 40 and a system controller 41. The system controller 41 controls the electronic endoscope system 10 as a whole, including the time controller 40.

[0020] The video processor 20 has a white light source 21, e.g., a xenon lamp, which emits white light W (normal or standard light), and an excitation light source 31, e.g., a laser light source, which emits excitation light F. A lamp power supply 26 applies the required voltage to the white light source 21 so that it emits the white light.

[0021] The white light W enters Fig. 1 from right to left through a diaphragm 22, a rotatable diaphragm 23 and a dichroic mirror 24 and falls on a condenser lens 25. The excitation light F, which in Fig. 1 is emitted from the excitation light source 31 in a scattered manner from bottom to top, is concentrated into a parallel light beam by a collimator lens 32. The (parallel) excitation light F, which is reflected by the dichroic mirror 24, travels in Fig. 1 similarly to the white light W from right to left and falls on the condenser lens 25. The white light W or the excitation light F, which is bundled by the condenser lens 25, falls on the entrance end 15B of the light guide 15.

[0022] The voltage applied to the white light source 21 controls whether the white light source 21 emits white light W. The amount of white light W emitted by the white light source 21 is controlled by the aperture 22, which is adjusted by a first motor 27. The first motor 27 is controlled by a first motor driver circuit 28.

[0023] As in Fig. As shown in Figure 2, the rotatable diaphragm 23 has a blocking region 23a and a transmitting region 23b, each formed over half the circumference of the diaphragm 23. If the blocking region 23a is introduced into the luminous flux of the white light W, the latter is blocked by the diaphragm 23 and does not fall onto the entrance end 15B. Conversely, if the transmitting region 23b is introduced into the luminous flux of the white light W, the white light W passes through the rotatable diaphragm 23 and falls onto the entrance end 15B. The diaphragm 23 is rotated at a uniform speed by a second motor 35. The second motor 35 is controlled by a second motor driver circuit 36.

[0024] The excitation light source 31 is controlled by a light source driver circuit 34. The light source driver circuit 34 determines whether and in what quantity the excitation light F is radiated onto the object.

[0025] The white light W or excitation light F, which falls on and passes through the light guide 15, is emitted from the exit end 15A, i.e., the distal end piece 11a, onto the tissue present in the organ, which constitutes the object to be examined. The white light W emitted from the end piece 11a is reflected by the object. The reflected white light is received by the objective lens 13 on a photosensor surface of the imaging device 14, so that the latter records a normal or standard image formed on the photosensor surface by the reflected white light. On the other hand, if the excitation light F is emitted from the end piece 11a onto the object, the object is excited and emits autofluorescence radiation.This autofluorescence radiation is received at the photosensor surface via the objective lens 13, so that the imaging device 14 records a fluorescence image generated on the photosensor surface from the autofluorescence radiation. The excitation light F reflected from the object is absorbed by the excitation light blocking filter 19 and thus does not fall on the imaging device 14. The imaging device 14 generates image signals in the form of analog signals corresponding to the standard image or the fluorescence image received by the photosensor surface of the imaging device 14. The imaging device 14 is, for example, an interlaced CCD, so that the imaging device 14 records a single odd field in a field period related to this odd field and a single even field in a field period related to this even field.The imaging device 14 is controlled by control signals supplied to it from a driver / control circuit 38. The imaging device 14 generates field signals, namely, odd-field or even-field-related image signals corresponding to a single field and comprising a plurality of pixel signals, each consisting of a luminance signal Y and color difference signals Cb and Cr (color signals). The field signals, after being subjected to various image processing processes in an image processing block 50, are output to the monitor 46 in the form of the display image.

[0026] The timing control 40 generates frame or full-screen signals Sg as well as field or half-screen signals Sf (cf. Fig. 7). The timing of the individual driver circuits in the video processor 20 is based on the frame signals Sg and the field signals Sf.

[0027] The video processor 20 has a mode switch 37 and a level switch 61. In this embodiment, the electronic endoscope system 10 enters an operating mode selected from among several operating modes by making a corresponding input to the mode switch 37. The image displayed on the monitor 46 changes according to the selected operating mode. For example, if the selected operating mode is the standard image mode, a standard image 71 is shown on the monitor 46 as a display image, as shown in Fig. 3. The standard image 71 represents those parts of the object that are illuminated with the white light W. In the standard image 71, the tissue (object) present in the organ is represented with a natural light color based on the reflected white light W, while the lumen D (hollow area) in the organ is represented with a black or dark color because the lumen D does not reflect the white light W.

[0028] If the selected operating mode is the fluorescence image mode, a fluorescence image 72 is shown on the monitor 46 as a display image, as shown in Fig. 4. The fluorescence image 72 is an image based on the autofluorescence radiation emitted by the tissue that has entered an excited state by the excitation light F. In the fluorescence image 72, the fluorescence emission from the abnormal tissue E is weaker than that from the normal tissue C. Accordingly, the abnormal tissue is identified based on the intensity of the fluorescence emission in the fluorescence image 72. However, the lumen D, which cannot emit fluorescence radiation, is comparatively dark in the fluorescence image 72, similar to the abnormal tissue E. Thus, the lumen D cannot be distinguished from the abnormal tissue E when considering the fluorescence image 72.

[0029] If the selected operating mode is the double image mode, a double image 73 is shown on the monitor 46 as a display image, as in Fig. 5. The double image 73 consists of the standard image 71 and the fluorescence image 72, which are displayed side by side.

[0030] If the selected operating mode is the synthesis image mode, a composite image or synthesis image 74 is shown on the monitor 46 as a display image, as shown in Fig. 6. In the synthesis image mode 74, the color difference signals Cb and Cr of each pixel are set to be equal to the color difference signals Cb and Cr of the corresponding pixel in the standard image 71. The luminance signal Ys of each pixel is obtained by mixing the luminance signal Yw of each pixel in the standard image 71 and the luminance signal Yf of the corresponding pixel in the fluorescent image 72 at a predetermined ratio.

[0031] The procedure for generating the synthesis image is described below using the Fig. 7 to 9 described in detail. Fig. 7 is a timing chart illustrating the method for generating image signals in the imaging device 14 for five frame periods when the synthetic image mode is selected as the operation mode. Hereinafter, the five frame periods are referred to as the first to fifth frame periods. For frame periods other than the first to fifth frame periods, the method for generating image signals is the same as that for the first to fifth frame periods. Field signals corresponding to the standard image are hereinafter referred to as "standard image signals WLn," while field signals corresponding to the fluorescent image are hereinafter referred to as "fluorescent image signals FLn." Furthermore, the frame period preceding the first frame period is referred to as the 0th frame period.

[0032] The frame signal Sg is output in the odd frame periods, i.e., the first, third, and fifth frame periods. It is not output in the even frame periods, i.e., the second and fourth frame periods. The field signal Sf is output in each frame period during the first half period (odd field period), while it is not output during the second half period (even field period). For example, one frame period is 1 / 30 of a second, so one field period is 1 / 60 of a second.

[0033] The aperture 23 is rotated based on the field signal Sf so that the white light W emitted by the white light source 21 passes through the pass band 23b during the odd field period, but is blocked by the blocking band 23a during the even field period. The excitation light source 31 is controlled by the field signal Sf so that it does not emit the excitation light F during the odd field period, but emits it during the even field period. Accordingly, the object is illuminated not with the excitation light F during the odd field period, but with the white light W. Furthermore, the object is illuminated not with the white light W during the even field period, but with the excitation light F.This means that the object is alternately illuminated either with the white light W or with the excitation light F in the respective of the two half-image periods, and this type of illumination runs continuously, as it were, nested within each other.

[0034] The imaging device 14 is controlled by the field signal Sf. The imaging device 14 stores the electrical charge corresponding to either the standard image or the fluorescent image generated on the photosensor surface. The imaging device 14 then converts the stored electrical charge into either the standard image signals WLn or the fluorescent image signals FLn in each field period.

[0035] In the odd field period, the object is illuminated with white light W, and the imaging device 14 captures the normal or standard image based on the white light W reflected from the object. Accordingly, in the odd field period, the standard image signals WLn corresponding to the standard image are generated in the imaging device 14 and supplied to the image processing block 50.

[0036] On the other hand, the object is illuminated with the excitation light F, and the imaging device 14 records the fluorescence image based on the autofluorescence radiation emitted by the object. Accordingly, in the even field period, the fluorescence image signals FLn corresponding to the fluorescence image are generated in the imaging device 14 and fed to the image processing block 50. In each of the two field periods of each individual frame, either the standard image signals WLn or the fluorescence image signals FLn are generated and output, so that the generation and output of these signals occur alternately.

[0037] Fig. 8 is a circuit diagram showing the image processing block 50. The standard image signals WLn or the fluorescent image signals FLn are input to a signal pre-processing circuit 51. In the signal pre-processing circuit 51, the image signals WLn and FLn undergo some mandatory image processing, including color adjustment, and are converted into digital image signals. The standard image signals WLn converted into digital image signals are converted into image signals corresponding to pseudo frames in a dummy image block 52 and a switching circuit 53. Similarly, the fluorescent image signals FLn converted into digital signals are converted into image signals corresponding to dummy frames.

[0038] The dummy image block 52 has a first and a second memory 52a and 52b, which are connected to the timing controller 40 via a memory control line. The timing controller 40 specifies the timing at which the image signals are stored in and read from the memories 52a and 52b.

[0039] The switching circuit 53 has a first switch 53a consisting of input terminals ml and m2 and an output terminal nl, and a second switch 53b consisting of input terminals m3 and m4 and an output terminal n2.

[0040] The signal preprocessing circuit 51 has four output terminals. Two of these four output terminals are connected to the first and second image memories 52a, 52b, respectively. The first memory 52a is connected to the input terminal m1, and the second memory 52b is connected to the input terminal m3. The other two of the aforementioned four output terminals are directly connected to the input terminal m2 and the input terminal m4, respectively. The two switches 53a and 53b are connected to the timing controller 40 via a switch control line. The timing controller 40 controls the timing of the two switches 53a and 53b.

[0041] Fig. Figure 9 is a timing diagram showing the process for generating dummy frames for five frame periods. The generation of a single dummy frame from the standard image signal WLn in the first frame period will be described below with reference to Figure Fig. 8 and Fig. 9. In the other frame periods, a single dummy frame is generated from the standard picture signals in the same way as for the first frame. Therefore, a description of this is omitted here.

[0042] During the odd field period, the first switch 53a connects the input terminal m2 to the output terminal n1. Then, the standard image signals WL1 generated in the imaging device 14 are supplied from the signal preprocessing circuit 51 via the input terminal m2 and the output terminal n1, i.e., not via the first memory 52a, to an AGC circuit 54 (AGC stands for automatic gain control). Furthermore, the imaging device 14 also supplies the standard image signals WL1 to the first memory 52a, where the standard image signals WL1 are stored during the odd field period.

[0043] In contrast, in the even field period, the first switch 53a connects the input terminal m1 to the output terminal n1. Then, the standard image signals WL1, which have been stored in the first memory 52a in the odd field period, are read out from the first memory 52a. This is shown in Fig. 9 by "MEMO." The read-out standard image signals WL1 are supplied to the AGC circuit 54 via the input terminal m1 and the output terminal n1. Namely, the standard image signals WL1 stored in the first memory 52a are read out as standard image signals. These standard image signals WL1 are considered to be generated in the even field period, since the imaging device 14 does not generate the standard image signals during the even field period.

[0044] As described above, in the first frame period, a dummy frame consisting of standard image signals is composed of one field consisting of the standard image signals WL1 (field signals) generated in the imaging device 14 and one field consisting of the standard image signals WL1 (field signals) read from the first memory 52a. The standard image signals constituting the resulting dummy frame are then supplied to the AGC circuit 54. The standard image signals WL1 supplied to the AGC circuit 54 in the odd or even field period are supplied to the image synthesis circuit 56 via the noise reduction circuit 55 in the odd or even field period, respectively, as described below.

[0045] In the following, with reference to the Fig. 8 and Fig. 9 describes the method for generating a single pseudo frame, which is related to the fluorescence image, in the first frame period. In the other frame periods, the respective pseudo frame, which consists of fluorescence image signals, is generated in the same way as for the first frame. Therefore, a description of this is omitted here.

[0046] In the odd field period, the second switch 53b connects the input terminal m3 to the output terminal n2. The second memory 52b stores the fluorescent image signals FL0 generated in the even field period of the 0th frame period. Therefore, the fluorescent image signals FL0 are read out from the second memory 52b and supplied to the AGC circuit 54 as fluorescent image signals. These fluorescent image signals FL0 are considered to be generated in the odd field period because the imaging device 14 does not generate the fluorescent image signals during the odd field period.

[0047] In the even field period, the second switch 53b connects the input terminal m4 to the output terminal n2. Subsequently, the signal preprocessing circuit 51 supplies the fluorescent image signals FL1 generated in the even field period to the AGC circuit 54 via the input terminal m4 and the output terminal n2, not via the second memory 52a. The fluorescent image signals FL1 are also supplied to the second memory 52b and stored there during this period. Furthermore, the fluorescent image signals FL1 stored in the second memory 52b are read out in the odd field period of the second frame period.

[0048] As described above, in the first frame period, a dummy frame composed of the fluorescent image signals is composed of a field composed of the fluorescent image signals FL0 (field signals) read from the second memory 52b and a field composed of the fluorescent image signals FL1 (field signals) generated in the imaging device 14. The resulting dummy frame composed of the fluorescent image signals is supplied to the AGC circuit 54. The fluorescent image signals FL0 or FL1 supplied to the AGC circuit 54 in the odd or even field period are supplied to the image synthesis circuit 56 via the noise reduction circuit 55 in the odd or even field period, respectively, as described below.

[0049] In the following, with reference to Fig. 8 describes the method for processing image signals that have been converted into image signals representing pseudo-frames in the odd field period of the first frame period. In the other half periods, the pseudo-frames are processed in the same way as in the odd field period of the first frame period, so a description of this is omitted here.

[0050] In the AGC circuit 54, a gain adjustment is performed such that the luminance level of the standard image signals WL1 matches that of the fluorescence image signals FL0. Thus, first, both the average of the luminance values ​​(luminance signals) of the pixel signals contained in the standard image signals WL1 and the average of the luminance values ​​(luminance signals) of the pixel signals contained in the fluorescence image signals FL0 are calculated. Subsequently, the gain of the luminance signals contained in the fluorescence image signals is adjusted. The individual luminance values ​​(luminance signals) of the pixel signals contained in the fluorescence image signals FL0 are multiplied by a coefficient so that the average of the luminance values ​​in the fluorescence image signals FL0 matches the average of the luminance values ​​in the standard image signals WL1.Generally, the luminance value of the fluorescence image is smaller than that of the standard image, so the above coefficient is set to be greater than 1 and the gain of the luminance signals in the fluorescence image signals FL0 is usually increased.

[0051] After the gain adjustment described above, the standard image signals WL1 and the fluorescent image signals FL0 are fed to the noise reduction circuit 55. The noise present in the fluorescent image signals FL0 inevitably increases in the AGC circuit 54 because the fluorescent image signals FL0 are amplified there. The noise reduction circuit 55 therefore reduces the noise present in the fluorescent image signals FL0. For this purpose, the noise reduction circuit 55 is, for example, a median filter. After this noise reduction, the fluorescent image signals FL0 are fed to the image synthesis circuit 56. In contrast, the noise present in the standard image signals WL1 is not increased in the AGC circuit 54 because the standard image signals WL1 are not amplified in the AGC circuit 54. Accordingly, the standard image signals WL1 are supplied to the image synthesis circuit 56 without their noise being reduced by the noise reduction circuit 55.

[0052] In the image synthesis circuit 56, the standard image signals WL1 are combined with the fluorescent image signals FL0 to form synthesis image signals. The color difference signals Cb and Cr of each pixel signal contained in the synthesis image signals are set to be equal to the color difference signals of the corresponding pixel signal contained in the standard image signals WL1.

[0053] On the other hand, the luminance signal Ys of each pixel signal included in the synthesized image signal is generated by mixing the luminance signal Yw of the corresponding pixel signal in the standard image signal WL1 and the luminance signal Yf of the corresponding pixel signal in the fluorescent image signal FL0 at a predetermined ratio. Thus, the luminance signal Ys of each pixel signal included in the synthesized image signal is generated according to the following formula (1). Ys=α×Yw+β×Yf(α+β=1, α≥0,β≥0)

[0054] According to formula (1), the luminance level of the synthesized image signals is maintained at the matching luminance level set in the AGC circuit 54 because α + β is set equal to 1. The values ​​of α and β can be set by an input to the level switch 61.

[0055] The synthesized image signals generated in the image synthesis circuit 56 are fed to a signal post-processing circuit 58, where they are converted into analog signals. The analog synthesized image signals are displayed as a synthesized image 74 on the monitor 46.

[0056] As in Fig. 6, the normal tissue C reflects the white light W when it is incident on the normal tissue C. In addition, the normal tissue C is capable of emitting strong fluorescence radiation when irradiated with the excitation light F. The normal tissue C is therefore displayed as a relatively bright area in the synthesis image 74.

[0057] Similar to normal tissue C, abnormal tissue E also reflects white light W when illuminated with white light W. In contrast, abnormal tissue E is unable to emit strong fluorescence radiation when irradiated with excitation light F. Therefore, abnormal tissue E is displayed as a comparatively dark area in synthesis image 74. Abnormal tissue E can therefore be distinguished from normal tissue C in synthesis image 74.

[0058] The luminance value of the synthesized image 74 depends not only on the luminance value of the fluorescence image, but also on the luminance value of the standard image. Therefore, in the synthesized image 74, the abnormal tissue E is brighter than the lumen D. The abnormal tissue E can therefore be distinguished from the lumen D in the synthesized image 74 because the lumen D neither emits autofluorescence radiation nor reflects white light.

[0059] The color difference signals Cb and Cr contained in the synthesis image signals are the same as in the standard image 71, so that the color reproduction of the synthesis image 74 is just as good as that of the standard image 71.

[0060] The luminance of a bleeding body part in the synthesis image 74 is similarly low to that of the abnormal tissue E, since the bleeding body part is not capable of emitting strong fluorescence. Therefore, the bleeding body part cannot be distinguished from the abnormal tissue E based solely on the luminance values ​​present in the synthesis image 74.

[0061] However, the bleeding body part is displayed in pure red, while the abnormal tissue E is displayed in the normal color, similar to the normal tissue C. This allows the bleeding body part to be distinguished from the abnormal tissue E in the synthesis image 74.

[0062] Since the values ​​for α and β can be set as desired by the operator using the level switch 61, the operator is able to determine the ratio in which the fluorescence image is synthesized or mixed into the resulting image.

[0063] The following describes the display image displayed when the operation mode is set to a mode other than the synthetic image mode. When the selected operation mode is the dual image mode, similarly to the image synthesis mode, either the white light W or the excitation light F is emitted in alternating sequence in each of the two field periods included in each frame period. Accordingly, the object is illuminated with the white light W in the odd field period, so that the standard image signals are generated in the odd field period. Conversely, the object is illuminated with the excitation light F in the even field period, so that the fluorescent image signals are generated in the even field period. The alternately generated standard image signals and fluorescent image signals are combined or synthesized to form the dual image 73.

[0064] The method for generating the double image 73 is described below. In the odd field period of the odd frame period, the standard image signals WLn output from the imaging device 14 are stored in the first memory 52a. In the even field period of the odd frame period, the fluorescent image signals FLn output from the imaging device 14 in the manner described above are stored in the first memory 52a.

[0065] In the odd field period of the even frame period, the standard image signals WLn output from the imaging device 14 are stored in the second memory 52b. In the even field period of the even frame period, the fluorescent image signals FLn output from the imaging device 14 in the manner described above are stored in the second memory 52b.

[0066] Both the standard image signals WLn and the fluorescent image signals FLn stored in the first memory 52a in the odd frame period are read out from the first memory 52a in the following even frame period. During image signal readout, the standard image signals WLn corresponding to one line and the fluorescent image signals FLn corresponding to one line are alternately and continuously read out and compressed into image signals corresponding to half a line. The standard image signals WLn corresponding to the half line are combined with the fluorescent image signals FLn corresponding to the half line to generate image signals corresponding to one line consisting of the standard image signals WLn corresponding to the half line and the fluorescent image signals FLn corresponding to the half line.This reading and combining is carried out continuously so that the double image signals are generated which correspond to the double image 73 consisting of the standard image and the fluorescence image arranged side by side, as shown. Fig. 5 shows.

[0067] Similarly, the standard image signals WLn and the fluorescent image signals FLn stored in the memory 52b in the even field period are read out and combined into the double image signals corresponding to the double image 73.

[0068] The double image signals are output to the monitor 46 in the form of the double image 73 via the AGC circuit 54, the noise reduction circuit 55, the image synthesis circuit 56, and the signal post-processing circuit 58. In this case, the AGC circuit 54 adjusts the gain of the double image signals, and the noise reduction circuit 55 reduces the noise of the double image signals; however, the image synthesis circuit 58 does not process the double image signal. The signal post-processing circuit 58 converts the double image signals into analog signals.

[0069] The following describes the case where the standard mode is selected as the operating mode. In this case, the white light W is continuously irradiated onto the object, so that the imaging device 14 generates the standard image signals in both the odd and even field periods. Accordingly, the standard image signals are processed in a predetermined manner without being converted into image signals representing the pseudo frames in the dummy image block 52. The standard image data is output to the monitor 46 as a standard image.

[0070] Similarly, when the fluorescence mode is selected as the operating mode, the excitation light F is continuously irradiated onto the object and the fluorescence image 72 is displayed on the monitor 46.

[0071] As described above, the image processing block 50 is capable of generating the standard image 71, the fluorescence image 72, the double image 73, and the synthesis image 74 without requiring complicated circuitry.

[0072] In this embodiment, the standard image is captured when the subject is illuminated with white light W, that is, normal light or standard light. Visible light other than white light W can also be used as the standard light emitted onto the subject. However, white light or visible light, which can largely be considered white light, is preferable.

[0073] The gain adjustment performed in the AGC circuit 54 can also be performed by methods other than the described method. For example, the individual luminance values ​​(luminance signals) of the pixel signals contained in the fluorescent image signals FL0 can each be multiplied by a coefficient so that the highest luminance value of all the pixel signals contained in the standard image signals WL1 matches the corresponding value of the fluorescent image signals FL0, in order to bring the luminance level of the standard image signals WL1 into line with that of the fluorescent image signals FL0. However, such a method does not promise more precise gain adjustment than the method described above, since a luminance value due to noise may represent the highest luminance value in the fluorescent image or the standard image.

[0074] In this embodiment, the color difference signals Cb and Cr are used as color signals. However, other types of color difference signals, such as color difference signals (U, V) or color difference signals (a, b), may also be used as color signals.

Claims

[1] Electronic endoscope system (10), comprising: - a video observation part (11); - an illumination device (21, 26, 31, 34) which emits standard light or excitation light from the video observation part (11) onto an object, wherein the standard light is reflected by the object and the excitation light brings the object into an excited state in which the object emits fluorescent radiation; - an imaging device (14) arranged in the video observation part (11) and receiving the reflected standard light and the fluorescent radiation to record a standard image (71) or a fluorescent image (72); - an image synthesis processor (56) that combines the standard image (71) and the fluorescence image (72) into a synthesis image (74) such that a color signal of the synthesis image (74) is equal to a color signal of the standard image (71) and a luminance signal of the synthesis image (74) is a mixture of a luminance signal of the standard image (71) and a luminance signal of the fluorescence image (72) in a predetermined ratio; and an adjustment processor (54) that adjusts the gain of the luminance signal of the standard image (71) and / or the fluorescence image (72). [2] Electronic endoscope system (10) according to claim 1, wherein - the adjustment processor (54) adjusts the gain of the luminance signal of the standard image (71) and / or the fluorescence image (72) so that the luminance level of the standard image (71) matches that of the fluorescence image (72), - wherein the luminance level of the synthesis image (74) is maintained at said matching luminance level. [3] The electronic endoscope system (10) according to claim 2, wherein the adjustment processor (54) adjusts the gain of the luminance signal so that the mean luminance value of the standard image (71) matches the mean luminance value of the fluorescence image (72). [4] An electronic endoscope system (10) according to any preceding claim, wherein the illumination device (21, 26, 31, 34) emits the standard image (71) in a predetermined period and the excitation light in another predetermined period; and the imaging device (14) captures the standard image (71) in this predetermined period and the fluorescence image (72) in this other predetermined period. [5] Electronic endoscope system (10) according to claim 4, wherein the illumination device (21, 26, 31, 34) alternately emits either the standard light or the excitation light in one of two regularly successive periods, so that the imaging device (14) alternately records either the standard image (71) or the fluorescence image (72) in one of the two regularly successive periods, and the image synthesis processor (56) combines the standard image (71) recorded in one of the two regularly successive periods with the fluorescence image (72) recorded in the subsequent or previous period. [6] Electronic endoscope system (10) according to claim 5, wherein the period is a field period. [7] An electronic endoscope system (10) according to claim 5 or 6, wherein standard image signals related to the standard image (71) which are acquired in said period are supplied to the image synthesis processor (56) not only in said period but also in the period following said period, fluorescence image signals related to the fluorescence image (72) which are recorded in said other period are supplied to the image synthesis processor (56) not only in this other period but also in the period following this other period, and the image synthesis processor (56) combines the standard image signals and the fluorescence image signals supplied to it in the same period. [8] Electronic endoscope system (10) according to one of the preceding claims, wherein the predetermined ratio is adjustable via an input switch (61).

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