Image processing apparatus, image processing method, and storage medium
An image processing apparatus performs first noise reduction processing on a plurality of radiation images corresponding to mutually-different radiation energies, generates a decomposition image by energy subtraction processing using the plurality of radiation images obtained by performing the first noise reduction processing, and performs second noise reduction processing on the decomposition image, wherein the second noise reduction processing uses a filter that differs from a filter used in the first noise reduction processing in at least one of size and type.
1. An image processing apparatus comprising:
a first processing unit configured to perform first noise reduction processing on a plurality of radiation images corresponding to mutually-different radiation energies;
a generating unit configured to generate a decomposition image by energy subtraction processing using the plurality of radiation images obtained by performing the first noise reduction processing; and
a second processing unit configured to perform second noise reduction processing on the decomposition image, the second noise reduction processing using a filter that differs from a filter used in the first noise reduction processing in at least one of size and type.
2. The image processing apparatus according to claim 1 ,
wherein the first noise reduction processing and the second noise reduction processing include at least one of a spatial filter and a temporal filter, and a kernel or a filter coefficient of the filter used in the second noise reduction processing is greater than a kernel or a filter coefficient of the filter used in the first noise reduction processing.
3. The image processing apparatus according to claim 1 ,
wherein in the first noise reduction processing, one of a spatial filter and a temporal filter is used, and in the second noise reduction processing, another of the spatial filter and the temporal filter is used.
4. The image processing apparatus according to claim 1 ,
wherein the decomposition image is a third decomposition image obtained by combining a thickness image of a first material, the thickness image of the first material being a first decomposition image obtained from the energy subtraction processing, with a thickness image of a second material, the thickness image of the second material being a second decomposition image, and
the third decomposition image is an image of a sum of a thickness of the first material and a thickness of the second material, one of the first material and the second material is bone, and another of the first material and the second material is soft tissue.
5. The image processing apparatus according to claim 1 ,
wherein the first processing unit performs the first noise reduction processing on the plurality of radiation images such that an edge of a structure detected from a radiation image to which the energy subtraction processing is not applied is maintained.
6. The image processing apparatus according to claim 1 ,
wherein the decomposition image is a third decomposition image obtained by combining a first decomposition image and a second decomposition image obtained from the energy subtraction processing, and
the generating unit generates an image corresponding to the first decomposition image or the second decomposition image based on a radiation image to which the energy subtraction processing is not applied and the third decomposition image to which the second noise reduction processing is applied, or generates an image corresponding to the second decomposition image based on the radiation image to which the energy subtraction processing is not applied and the first decomposition image to which the second noise reduction processing is applied.
7. The image processing apparatus according to claim 1 ,
wherein using a radiation image to which the energy subtraction processing is not applied and a predetermined constraint, the generating unit generates a pseudo decomposition image corresponding to the decomposition image obtained from the energy subtraction processing, and
a combining ratio pertaining to combining of the decomposition image obtained by performing the second noise reduction processing and the pseudo decomposition image is determined using a second decomposition image obtained from the energy subtraction processing.
8. The image processing apparatus according to claim 7 ,
wherein the generating unit generates an image corresponding to the second decomposition image based on an image obtained from the combining at the combining ratio determined and the radiation image to which the energy subtraction processing is not applied.
9. An image processing apparatus comprising:
a generating unit that generates a decomposition image by energy subtraction processing using a plurality of radiation images corresponding to mutually-different radiation energies, and generates a pseudo decomposition image using a radiation image to which the energy subtraction processing is not applied and a predetermined constraint; and
a determining unit that, using the decomposition image, determines a combining ratio pertaining to combining the decomposition image and the pseudo decomposition image.
10. The image processing apparatus according to claim 9 ,
wherein the determining unit determines a combining ratio pertaining to combining a third decomposition image, obtained by combining a first decomposition image and a second decomposition image obtained from the energy subtraction processing, with the pseudo decomposition image, using the second decomposition image.
11. The image processing apparatus according to claim 10 ,
wherein the first decomposition image is a thickness image of a first material, and the second decomposition image is a thickness image of a second material, and
the generating unit generates the pseudo decomposition image using an assumption that a thickness of the second material is 0 as the predetermined constraint.
12. The image processing apparatus according to claim 10 ,
wherein the determining unit determines the combining ratio based on a comparison of each of pixel values in the second decomposition image with a threshold.
13. The image processing apparatus according to claim 10 ,
wherein the determining unit determines the combining ratio to be a first value when a pixel value in the second decomposition image exceeds a predetermined threshold and determines the combining ratio to be a second value different from the first value in other cases, or changes the combining ratio from a first value to a second value different from the first value in accordance with a pixel value in the second decomposition image changing from a first threshold to a second threshold.
14. The image processing apparatus according to claim 10 , further comprising:
a processing unit that applies noise reduction processing to the second decomposition image,
wherein the determining unit determines the combining ratio based on the second decomposition image from after the noise reduction processing.
15. The image processing apparatus according to claim 9 ,
wherein the plurality of radiation images are generated using a plurality of radiation images obtained by sampling and holding at a plurality of timings including during radiation emission and a timing after completion of emission, with respect to a single instance of radiation emission, and
a radiation image obtained at the timing after completion of emission is used as the radiation image to which the energy subtraction processing is not applied.
16. The image processing apparatus according to claim 9 ,
wherein the radiation image to which the energy subtraction processing is not applied is generated by weighting and combining the plurality of radiation images, or one of the plurality of radiation images is used as the radiation image to which the energy subtraction processing is not applied.
17. An image processing method comprising:
performing first noise reduction processing on a plurality of radiation images corresponding to mutually-different radiation energies;
generating a decomposition image by energy subtraction processing using the plurality of radiation images obtained by performing the first noise reduction processing; and
performing second noise reduction processing on the decomposition image, the second noise reduction processing using a filter that differs from a filter used in the first noise reduction processing in at least one of size and type.
18. A non-transitory computer readable storage medium storing a program for causing a computer to execute steps in the method according to claim 17 .
19. An image processing method comprising:
generating a decomposition image by energy subtraction processing using a plurality of radiation images corresponding to mutually-different radiation energies;
generating a pseudo decomposition image using a radiation image to which the energy subtraction processing is not applied and a predetermined constraint; and
determining, using the decomposition image, a combining ratio pertaining to combining of the decomposition image and the pseudo decomposition image.
20. A non-transitory computer readable storage medium storing a program for causing a computer to execute steps in the method according to claim 19 .