Medical image processing apparatus and medical image pickup system

A medical image processing apparatus of the present invention is a medical image processing apparatus to which a plurality of color components corresponding to frame-sequentially picked-up images of an object are time-sequentially inputted while maintaining periodicity thereof, including a color component storage section that can store a first color component inputted to the medical image processing apparatus at one timing and a second color component, which is a component of the same wavelength band as that of the first color component inputted to the medical image processing apparatus at timing preceding the one timing by one cycle or more, and an image correction processing section that simultaneously reads the first color component and the second color component stored in the color component storage section and performs image correction processing.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a medical image processing apparatus and a medical image pickup system, and more particularly, to a medical image processing apparatus and a medical image pickup system capable of frame-sequentially acquiring color components of an object.

2. Description of the Related Art

Medical systems made up of an endoscope and a medical image processing apparatus or the like are conventionally mainly used by an operator or the like to observe the inside of a living body as an object to be examined. Examples of the endoscope system used for the above described application include an electronic endoscope apparatus proposed in Japanese Patent Application Laid-Open Publication No. 5-237059.

The electronic endoscope apparatus described in Japanese Patent Application Laid-Open Publication No. 5-237059 has a configuration based on a so-called frame sequential image pickup method (hereinafter referred to as “frame sequential method”), and to be more specific, is configured by including illumination means for time-sequentially illuminating an object with a plurality of illumination lights of different wavelength bands, a solid image pickup device that picks up an image of the object illuminated with the illumination lights from the illumination means and reading means for dividing information of the solid image pickup device into information of odd-numbered fields and information of even-numbered fields through interlace scanning and alternately reading the information.

SUMMARY OF THE INVENTION

A medical image processing apparatus according to the present invention is a medical image processing apparatus to which a plurality of color components corresponding to frame-sequentially picked-up images of an object are time-sequentially inputted while maintaining periodicity thereof, including a color component storage section that can store a first color component inputted to the medical image processing apparatus at one timing and a second color component, which is a component of the same wavelength band as that of the first color component inputted to the medical image processing apparatus at timing preceding the one timing by one cycle or more, and an image correction processing section that simultaneously reads the first color component and the second color component stored in the color component storage section and performs image correction processing.

A medical image pickup system according to the present invention includes a light source section that time-sequentially outputs a plurality of illumination lights of different wavelength bands, a color component acquiring section that can receive returned light from an object illuminated with the illumination lights and acquires color components of the object corresponding to the returned light, a color component storage section that can store a first color component acquired at one timing corresponding to a cycle in which light of the same wavelength band is outputted from the light source section and a second color component, which is a component of the same wavelength band as that of the first color component acquired at timing preceding the one timing by one cycle or more and an image correction processing section that simultaneously reads the first color component and the second color component stored in the color component storage section and performs image correction processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIGS. 1 to 7are related to the embodiment of the present invention.FIG. 1is a diagram illustrating an example of a configuration of main parts of an endoscope apparatus as a medical image pickup system for which a medical image processing apparatus according to the present embodiment is used.FIG. 2is a diagram illustrating an example of a configuration of a rotation filter of the endoscope apparatus inFIG. 1.FIG. 3is a diagram illustrating an example of transmission characteristics of each filter of the rotation filter inFIG. 2.FIG. 4is a diagram illustrating an example of a configuration of the color component storage circuit according to the present embodiment.FIG. 5is a diagram illustrating write timing and read timing of each color component in the color component storage circuit inFIG. 4.FIG. 6is a diagram illustrating an example different from that inFIG. 4of the configuration of the color component storage circuit according to the present embodiment.FIG. 7is a diagram illustrating write timing and read timing of each color component in the color component storage circuit inFIG. 6.

As shown inFIG. 1, an endoscope apparatus1as a medical image pickup system of the present embodiment is configured by including, as main components, an endoscope2that can be inserted into a living body, picks up an image of an object such as living tissue existing in the living body and outputs the image of the living tissue as an image pickup signal, a light source apparatus3that supplies illumination light for illuminating the object to the endoscope2via a light guide6inserted in the endoscope2, a video processor4that performs signal processing according to the image pickup signal outputted from the endoscope2and outputs the image pickup signal after the signal processing as a video signal and a monitor5that displays the image of the object picked up by the endoscope2based on the video signal outputted from the video processor4.

The endoscope2is configured by including an illumination optical system21that outputs illumination light supplied from the light source apparatus3and transmitted by the light guide6, an objective optical system22that forms an image of the object illuminated with illumination light outputted from the illumination optical system21and a CCD (charge coupled device)23placed at an image forming position of the objective optical system22.

The progressive scanning (non-interlace scanning) CCD23picks up an image of the object illuminated with illumination light time-sequentially outputted from the illumination optical system21and outputs the image of the object as an image pickup signal. Thus, the CCD23as the image pickup device outputs information of odd-numbered fields and information of even-numbered fields of one color component acquired for one exposure period as an image pickup signal during a read period after the exposure period.

That is, the CCD23has a function as a color component acquiring section that can receive returned light from the object illuminated with illumination light time-sequentially outputted from the illumination optical system21and acquires color components of the object according to the returned light.

The light source apparatus3as a light source section has a lamp31, a heat radiation cut filter32that cuts heat radiation of white color light emitted from the lamp31, a diaphragm apparatus33, a rotation filter34that transforms the white color light that has passed through the diaphragm apparatus33into frame sequential illumination light, a condensing optical system35that condenses the frame sequential illumination light that has passed through the rotation filter34and outputs the illumination light to the light guide6, a rotation filter motor36that drives the rotation filter34to rotate and a rotation filter control circuit37.

The lamp31is a light source that can emit white color light and is made up of, for example, a xenon lamp.

The diaphragm apparatus33adjusts the light amount of the white color light that has passed through the heat radiation cut filter32based on a diaphragm control signal outputted from the video processor4.

As shown inFIG. 2, the rotation filter34is configured into a disk shape, the center of which is the axis of rotation. Furthermore, as shown inFIG. 2, the rotation filter34is configured by including an R filter34rthat allows light in a red color wavelength band to transmit therethrough, a G filter34gthat allows light in a green color wavelength band to transmit therethrough and a B filter34bthat allows light in a blue color wavelength band to transmit therethrough, each filter being provided in a circumferential direction of the perimeter.

The R filter34ris configured so as to allow light in the red color wavelength band, for example, light from 600 nm to 700 nm as shown inFIG. 3to transmit therethrough.

The G filter34gis configured so as to allow light in the green color wavelength band, for example, light from 500 mm to 600 mm as shown inFIG. 3to transmit therethrough.

The B filter34bis configured so as to allow light in the blue color wavelength band, for example, light from 400 nm to 500 nm as shown inFIG. 3to transmit therethrough.

The rotation filter control circuit37controls the rotation driving of the rotation filter motor36and outputs a synchronization signal synchronized with the rotation of the rotation filter34to the video processor4. With the respective sections of the light source apparatus3having the aforementioned configurations, the white color light that has transmitted through the R filter34r, the G filter34gand the B filter34bis condensed by the condensing optical system35as frame sequential illumination light made up of R (red) light, G (green) light and B (blue) light and then outputted to the light guide6.

The video processor4is provided with a CCD driver41that drives the CCD23of the endoscope2, an amplifier42that amplifies an image pickup signal outputted from the CCD23, a process circuit43that applies processing such as correlation double sampling to the image pickup signal outputted from the amplifier42and an A/D converter44that converts the image pickup signal outputted from the process circuit43to a digital image signal.

Furthermore, the video processor4is provided with a color component storage circuit61that stores the image signal outputted from the A/D converter44for each color component and a calculation processing circuit62.

As shown inFIG. 4, the color component storage circuit61as a color component storage section is configured by including a selector61sthat selectively outputs color components included in the image signal from the A/D converter44based on a timing signal outputted from a timing generator49, an R component storage circuit61rthat stores an R component included in the image signal from the selector61s, a G component storage circuit61gthat stores a G component included in the image signal from the selector61sand a B component storage circuit61bthat stores a B component included in the image signal from the selector61s.

The R component storage circuit61rhas memories61r1and61r2to store two R components; a first R component inputted at predetermined timing and a second R component inputted at timing preceding the predetermined timing by one cycle.

The G component storage circuit61ghas memories61g1and61g2to store two G components; a first G component inputted at predetermined timing and a second G component inputted at timing preceding the predetermined timing by one cycle.

The B component storage circuit61bhas memories61b1and61b2to store two B components; a first B component inputted at predetermined timing and a second B component inputted at timing preceding the predetermined timing by one cycle.

The calculation processing circuit62sequentially reads at different timing the two R components (first R component and second R component) stored in the R component storage circuit61r, the two G components (first G component and second G component) stored in the G component storage circuit61gand the two B components (first B component and second B component) stored in the B component storage circuit61bsequentially at different timings based on timing signals outputted from the timing generator49, applies image correction processing such as noise reduction processing and/or motion interpolation processing or the like to information on the read color components and then outputs the color component signals after the image correction processing to a white balance circuit45.

Furthermore, the video processor4is provided with the white balance circuit45that applies white balance processing to the color component signals outputted from the calculation processing circuit62, a synchronization circuit46that temporarily stores and synchronizes the color component signals sequentially outputted from the white balance circuit45, an image processing circuit47, a D/A converter48, the timing generator49that outputs timing signals corresponding to synchronization signals outputted from the rotation filter control circuit37of the light source apparatus3to the respective sections of the aforementioned video processor4and a dimming circuit52.

The synchronization circuit46is configured by including a selector46a, and memories46b,46cand46d.

The selector46asequentially outputs the color component signals outputted from the white balance circuit45to the memories46b,46cand46dbased on the timing signals outputted from the timing generator49.

The memories46b,46cand46dare configured as an R channel memory, a G channel memory and a B channel memory respectively. That is, the color component signal inputted to the memory46bis stored as a red component, the color component signal inputted to the memory46cis stored as a green component and the color component signal inputted to the memory46dis stored as a blue component.

The memories46b,46cand46dstore and synchronize the color component signals outputted from the selector46abased on the timing signals outputted from the timing generator49.

The image processing circuit47reads color component signals corresponding to one frame out of the respective color component signals stored in the synchronization circuit46, performs processing such as gamma correction processing on the color component signals corresponding to one frame and then outputs the processed color component signals corresponding to one frame to the D/A converter48.

The D/A converter48converts the respective color component signals outputted from the image processing circuit47to analog video signals and outputs the analog video signals.

The dimming circuit52outputs a diaphragm control signal for performing brightness control according to an observation of white color light based on the image pickup signal outputted from the process circuit43to the diaphragm apparatus33.

Next, operations of the endoscope apparatus1will be described.

First, the operator et al. turns on power to the respective sections of the endoscope apparatus1, that is, the endoscope2, the light source apparatus3, the video processor4and the monitor5to activate the respective sections.

When the light source apparatus3is started, frame sequential illumination light made up of R light, G light and B light is outputted to the light guide6. Furthermore, along with the starting of the light source apparatus3, a synchronization signal synchronized with the rotation of the rotation filter34is outputted from the rotation filter control circuit37to the video processor4.

The frame sequential illumination light made up of R light, G light and B light is outputted to an object via the light guide6and the illumination optical system21.

The image of the object illuminated with the frame sequential illumination light made up of R light, G light and B light is formed by the objective optical system22, picked up by the CCD23and then sequentially outputted to the video processor4as an image pickup signal.

The image pickup signal outputted to the video processor4is amplified by the amplifier42, subjected to processing such as correlation double sampling by the process circuit43, converted to a digital image signal by the A/D converter44, and then inputted to the color component storage circuit61.

Here, write timing and read timing of each color component in the color component storage circuit61will be described. Immediately after the starting of the video processor4(initial state), suppose none of the color components is stored in each memory of the R component storage circuit61r, the G component storage circuit61gand the B component storage circuit61b. Hereinafter, suppose the selector61sperforms a write (“Write” shown inFIG. 5) to the color component storage circuit61and the calculation processing circuit62performs a read (“Read” shown inFIG. 5) from the color component storage circuit61.

First, as shown inFIG. 5, immediately after the starting of the video processor4, a color component R1corresponding to the image of the object of R light at the first rotation (first cycle) of the rotation filter34is written to the memory61r1, a color component G1corresponding to the image of the object of G light at the first rotation (first cycle) of the rotation filter34is written to the memory61g1and a color component B1corresponding to the image of the object of B light at the first rotation (first cycle) of the rotation filter34is written to the memory61b1.

After that, as shown inFIG. 5, a color component R2corresponding to the image of the object of R light at the second rotation (second cycle) of the rotation filter34is written to the memory61r2.

As shown inFIG. 5, the color components R1and R2stored in the memory61r1and the memory61r2are read at the same timing as a color component G2corresponding to the image of the object of G light at the second rotation (second cycle) of the rotation filter34is written to the memory61g2.

As shown inFIG. 5, the color components G1and G2stored in the memories61g1and61g2are read at the same timing as a color component B2corresponding to the image of the object of B light at the second rotation (second cycle) of the rotation filter34is written to the memory61b2.

As shown inFIG. 5, the color components B1and B2stored in the memories61b1and61b2are read at the same timing as a color component R3corresponding to the image of the object of R light at the third rotation (third cycle) of the rotation filter34is overwritten to the memory61r1.

As shown inFIG. 5, the color components R3and R2stored in the memories61r1and61r2are read at the same timing as a color component G3corresponding to the image of the object of G light at the third rotation (third cycle) of the rotation filter34is overwritten to the memory61g1.

As shown inFIG. 5, the color components G3and G2stored in the memories61g1and61g2are read at the same timing as a color component B3corresponding to the image of the object of B light at the third rotation (third cycle) of the rotation filter34is overwritten to the memory61b1.

The above described writes and reads are repeatedly performed, and two R components; the first R component inputted at predetermined timing and the second R component inputted at timing preceding the predetermined timing by one cycle are thereby stored in the memories61r1and61r2.

The above described writes and reads are repeatedly performed, and two G component; the first G component inputted at predetermined timing and the second G component inputted at timing preceding the predetermined timing by one cycle are thereby stored in the memories61g1and61g2.

The above described writes and reads are repeatedly performed, and two B components; the first B component inputted at predetermined timing and the second B component inputted at timing preceding the predetermined timing by one cycle are thereby stored in the memories61b1and61b2.

On the other hand, the calculation processing circuit62sequentially reads the first and second R components, the first and second G components, and the first and second B components at the aforementioned different timings with reference toFIG. 5and then applies image correction processing to the information on the read color components.

Here, noise reduction processing will be described as an example of image correction processing performed by the calculation processing circuit62. Suppose the following descriptions on the image correction processing will be given by taking mainly the processing on the first and second R components as an example.

After acquiring a difference image between the first and the second R components, the calculation processing circuit62applies a Fourier transform to the difference image, and thereby converts the difference image from real space data to spatial frequency data. That is, a motion component of real space data having high correlation with neighboring pixels is converted as a peak component which is intensively distributed on a specific frequency domain of spatial frequency data. On the other hand, a noise component of real space data having low correlation with neighboring pixels is converted as a component substantially uniformly distributed over each frequency domain of spatial frequency data.

After extracting each component remaining after removing the peak component as a noise component of the real space data, the calculation processing circuit62performs processing of subtracting each brightness value included in the noise component from the second R component. The calculation processing circuit62then outputs the second R component after applying the processing to the white balance circuit45as a color component signal.

The above described noise reduction processing is applicable not only to the R component but also to the G component and the B component likewise.

The calculation processing circuit62can improve S/N for each color component by performing the above described noise reduction processing as image correction processing.

Furthermore, motion interpolation processing will be described as an example of image correction processing performed by the calculation processing circuit62.

After acquiring a difference image between the first R component and the second R component, the calculation processing circuit62extracts a region surrounded by a portion where the brightness value is not 0 as a region where a motion component is estimated to have been generated.

The calculation processing circuit62acquires a reference region of the second R component as a block based on the extracted region and then detects a region having the highest similarity to the block in the first R component. The calculation processing circuit62then calculates a motion vector M(dx, dy) of the block based on the coordinate position of the block and the coordinate position of the region having the highest similarity to the block.

In this case, when the brightness value at a position (x, y) of a second R component Ri is assumed to be Ri(x, y) and the brightness value at a position (x, y) of a first R component Ri+1 is assumed to be Ri+1(x, y), the relationship expressed by the following equation (1) holds between Ri(x, y), Ri+1(x, y) and motion vector M(dx, dy).
Ri+1(x,y)=Ri(x+dx,y+dy)  (1)

Since the above described equation (1) holds, when, for example, the aforementioned motion vector M(dx, dy) is trisected, a brightness value Rit1(x, y) at a position (x, y) of a first intermediate image Rit1interpolated between the second R component and the first R component is expressed by the following equation (2).
Rit1(x,y)=Ri(x+dx×1/3,y+dy×1/3)  (2)

Furthermore, a brightness value Rit2(x, y) at a position (x, y) of a second intermediate image Rit2interpolated between the second R component and the first R component is expressed by the following equation (3).
Rit2(x,y)=Ri(x+dx×2/3,y+dy×2/3)  (3)

However, when each intermediate image interpolated between the second R component and the first R component is calculated by the above described equation (2) and equation (3), there is a possibility that any one of an overlapping pixel through which the block passes a plurality of times and a gap pixel through which the block never passes may occur according to the deviation of the motion vector M(dx, dy). (The number of times the block passes therethrough can be regarded as having the same value as the number of times the motion vector M crosses, for example). The presence of the overlapping pixel and the gap pixel causes pixels having wrong brightness values to be outputted when each intermediate image is calculated.

Therefore, the calculation processing circuit62performs processing of assigning a brightness value of the pixel at the same position of the second R component to the brightness values of the overlapping pixel and the gap pixel in each intermediate image detected based on the number of times the block passes. This allows the calculation processing circuit62to avoid outputting of pixels having wrong brightness values when each intermediate image is calculated.

Here, timing at which each intermediate image is calculated will be described by taking the timing chart inFIG. 5as an example.

The calculation processing circuit62reads the color components R1and R2at substantially the same timing as the color component R2corresponding to the image of the object of R light at the second rotation (second cycle) of the rotation filter34is written to the memory61r2, calculates a brightness value R1(x, y) at a position (x, y) of the color component R1, a brightness value R2(x, y) at a position (x, y) of the color component R2and the motion vector M(dx, dy) and outputs the color component R1to the white balance circuit45as a color component signal.

Furthermore, the calculation processing circuit62performs the calculation using the above described equation (2) at timing at which the color component G2corresponding to the image of the object of G light at the second rotation (second cycle) of the rotation filter34is written to the memory61g2, thereby generates a first intermediate image R1t1interpolated between the color component R1and the color component R2and outputs the first intermediate image R1t1to the white balance circuit45as a color component signal.

Furthermore, the calculation processing circuit62performs the calculation using the above described equation (3) at timing at which the color component B2corresponding to the image of the object of B light at the second rotation (second cycle) of the rotation filter34is written to the memory61b2, thereby generates a second intermediate image R1t2interpolated between the color component R1and the color component R2and outputs the second intermediate image R1t2to the white balance circuit45as a color component signal.

The calculation processing circuit62then reads the color components R3and R2at substantially the same timing as the color component R3corresponding to the image of the object of R light at the second rotation (third cycle) of the rotation filter34is written to the memory61r1, calculates a brightness value R2(x, y) at a position (x, y) of the color component R2, a brightness value R3(x, y) at a position (x, y) of the color component R3and a new motion vector M(dx, dy) and outputs the color component R2to the white balance circuit45as a color component signal.

That is, when the timing chart inFIG. 5is taken as an example, the calculation processing circuit62generates (and outputs) two intermediate images of R1t1and R1t2in synchronization with the timing at which a color component other than the R component is written to the color component storage circuit61after the color component R1is outputted until the color component R2is outputted and thereby performs motion interpolation on the R component.

The above described motion interpolation processing is applicable not only to the R component but also to the G component and the B component likewise.

The calculation processing circuit62performs the above described motion interpolation processing as image correction processing, and can thereby improve time resolution in each color component.

As the image correction processing, the calculation processing circuit62of the present embodiment may perform any one of noise reduction processing and motion interpolation processing or may perform motion interpolation processing after performing noise reduction processing.

On the other hand, each color component signal outputted from the calculation processing circuit62is subjected to white balance processing by the white balance circuit45, synchronized by the synchronization circuit46, subjected to processing such as gamma correction processing by the image processing circuit47, converted to an analog video signal by the D/A converter48and then outputted to the monitor5.

As described above, the endoscope apparatus1of the present embodiment has a frame sequential configuration capable of time-sequentially acquiring color components having information on odd-numbered fields and information on even-numbered fields and performing image correction processing using a first color component at one timing according to the rotation cycle of the rotation filter of the light source apparatus and a second color component having the same color (wavelength band) as the first color component at timing preceding the one timing by one cycle. As a result, the endoscope apparatus1of the present embodiment can appropriately perform image correction processing in a frame sequential configuration.

In the frame sequential configuration, when image correction processing is performed every timing at which all color components of one frame are updated, it is not until a period combining at least a period until information corresponding to a total of 6 fields made up of information on odd-numbered fields and information on even-numbered fields of three color components of red (R), green (G) and blue (B) is acquired and a period used for calculation of the image correction processing elapses that it is possible to obtain one image after the image correction processing for the first time. That is, in the frame sequential configuration, when image correction processing is performed every timing at which all color components of one frame are updated, there are problems such as a reduction of the number of times processing is performed per unit time and/or a reduction of frame rate when a moving image is outputted.

On the other hand, unlike image correction processing that is performed every timing at which all color components of one frame are updated, the endoscope apparatus1of the present embodiment is configured, as described above, to start image correction processing at a point in time when both the first color component at one timing corresponding to the rotation cycle of the rotation filter of the light source apparatus and the second color component of the same color (wavelength band) as that of the first color component at timing preceding the one timing by one cycle are present. Therefore, the endoscope apparatus1of the present embodiment can improve the number of times image correction processing is performed per unit time while suppressing the reduction of frame rate when a moving image is outputted.

Instead of the color component storage circuit61only applicable to a case where the CCD23is a progressive scanning (non-interlace scanning) CCD, the video processor4of the present embodiment may also be provided with, for example, a color component storage circuit61A shown inFIG. 6capable of appropriately performing image correction processing when the CCD23is an interlace scanning CCD.

As shown inFIG. 6, the color component storage circuit61A as the color component storage section is configured by including a selector61sthat selectively outputs a color component included in an image signal from the A/D converter44based on a timing signal outputted from the timing generator49, an R component storage circuit161rthat stores an R component included in the image signal from the selector61s, a G component storage circuit161gthat stores a G component included in the image signal from the selector61sand a B component storage circuit161bthat stores a B component included in the image signal from the selector61s.

The R component storage circuit161rhas memories61r1,61r2,61r3and61r4for storing four R components; an R component of a first odd-numbered field inputted at predetermined first timing, an R component of a second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles, an R component of a first even-numbered field inputted at predetermined second timing and an R component of a second even-numbered field inputted at timing preceding the predetermined second timing by two cycles.

The G component storage circuit161ghas memories61g1,61g2,61g3and61g4for storing four G components; a G component of the first odd-numbered field inputted at predetermined first timing, a G component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles, a G component of the first even-numbered field inputted at predetermined second timing and a G component of the second even-numbered field inputted at timing preceding the predetermined second timing by two cycles.

The G component storage circuit161ghas memories61g1,61g2,61g3and61g4for storing four G components; a G component of the first odd-numbered field inputted at predetermined first timing, a G component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles, a G component of the first even-numbered field inputted at predetermined second timing and a G component of the second even-numbered field inputted at timing preceding the predetermined second timing by two cycles.

The B component storage circuit161bhas memories61b1,61b2,61b3and61b4for storing four B components; a B component of the first odd-numbered field inputted at predetermined first timing, a B component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles, a B component of the first even-numbered field inputted at predetermined second timing and a B component of the second even-numbered field inputted at timing preceding the predetermined second timing by two cycles.

Here, write timing and read timing of each color component in the color component storage circuit61A will be described. In an initial state, suppose none of the color components is stored in each memory of the R component storage circuit161r, the G component storage circuit161gand the B component storage circuit161b. Hereinafter, suppose the selector61sperforms a write (“Write” shown inFIG. 7) to the color component storage circuit61A and the calculation processing circuit62performs a read (“Read” shown inFIG. 7) from the color component storage circuit61A.

First, as shown inFIG. 7, in an initial state, a color component Ro1of the odd-numbered field corresponding to the image of the object of R light at the first rotation (first cycle) of the rotation filter34is written to the memory61r1, a color component Go1of the odd-numbered field corresponding to the image of the object of G light at the first rotation (first cycle) of the rotation filter34is written to the memory61g1and a color component Bo1of the odd-numbered field corresponding to the image of the object of B light at the first rotation (first cycle) of the rotation filter34is written to the memory61b1.

Furthermore, as shown inFIG. 7, a color component Re1of the even-numbered field corresponding to the image of the object of R light at the second rotation (second cycle) of the rotation filter34is written to the memory61r2, a color component Gel of the even-numbered field corresponding to the image of the object of G light at the second rotation (second cycle) of the rotation filter34is written to the memory61g2and a color component Be1of the even-numbered field corresponding to the image of the object of B light at the second rotation (second cycle) of the rotation filter34is written to the memory61b2.

After that, as shown inFIG. 7, a color component Ro2of the odd-numbered field corresponding to the image of the object of R light at the third rotation (third cycle) of the rotation filter34is written to the memory61r3.

As shown inFIG. 7, the color components Ro1and Ro2stored in the memories61r1and61r3are read at the same timing as the color component Go2of the odd-numbered field corresponding to the image of the object of G light at the third rotation (third cycle) of the rotation filter34is written to the memory61g3.

As shown inFIG. 7, the color components Go1and Go2stored in the memories61g1and61g3are read at the same timing as the color component Bo2of the odd-numbered field corresponding to the image of the object of B light at the third rotation (third cycle) of the rotation filter34is written to the memory61b3.

As shown inFIG. 7, the color components Bo1and Bo2stored in the memories61b1and61b3are read at the same timing as the color component Re2of the even-numbered field corresponding to the image of the object of R light at the fourth rotation (fourth cycle) of the rotation filter34is written to the memory61r4.

By repeating writes and reads related to the above described R component of the odd-numbered field, two R components are stored in the memories61r1and61r3; the R component of the first odd-numbered field inputted at predetermined first timing and the R component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles. Furthermore, by repeating writes and reads related to the above described R component of the even-numbered field, two R components are stored in the memories61r2and61r4; the R component of the first even-numbered field inputted at predetermined second timing and the R component of the second odd-numbered field inputted at timing preceding the predetermined second timing by two cycles.

By repeating writes and reads related to the above described G component of the odd-numbered field, two G components are stored in the memories61g1and61g3; the G component of the first odd-numbered field inputted at predetermined first timing and the G component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles. Furthermore, by repeating writes and reads related to the above described G component of the even-numbered field, two G components are stored in the memories61g2and61g4; the G component of the first even-numbered field inputted at predetermined second timing and the G component of the second odd-numbered field inputted at timing preceding the predetermined second timing by two cycles.

By repeating writes and reads related to the above described B component of the odd-numbered field, two B components are stored in the memories61b1and61b3; the B component of the first odd-numbered field inputted at predetermined first timing and the B component of the second odd-numbered field inputted at timing preceding the predetermined first timing by two cycles. Furthermore, by repeating writes and reads related to the above described B component of the even-numbered field, two B components are stored in the memories61b2and61b4; the B component of the first even-numbered field inputted at predetermined second timing and the B component of the second odd-numbered field inputted at timing preceding the predetermined second timing by two cycles.

The endoscope2of the present embodiment is not limited to one having an (e.g., elongated) insertion portion that allows the light guide6for transmitting red, green and blue illumination light time-sequentially supplied from the light source apparatus3to be inserted therein, but the endoscope2may also be a capsule-shaped one that incorporates red, green and blue LEDs that time-sequentially emit light.

Furthermore, in the present embodiment, any one of R light, G light and B light as frame sequential light may be substituted by special light such as excitation light for generating fluorescent light from living tissue or light in an infrared region.

The present invention is not limited to the aforementioned embodiment and it goes without saying that various modifications and applications can be made without departing from the spirit and scope of the invention.