Imaging data processing apparatus and method
An image processing apparatus comprises processing circuitry configured to: obtain an irradiance volume representative of virtual light cast into a volumetric imaging data set, the irradiance volume comprising a respective irradiance value for each of a plurality of points in the irradiance volume; determine, for each of a plurality of reference points in the irradiance volume, a respective value for an accuracy measure, wherein the value for the accuracy measure at each reference point is representative of an accuracy with which irradiance has been determined at or near that reference point; and perform a rendering process using the irradiance volume, wherein the rendering process is performed in dependence on the determined values for the accuracy measure.
1. An image processing apparatus comprising:
processing circuitry configured to:
obtain an irradiance volume representative of virtual light cast into a volumetric imaging data set, the irradiance volume comprising a respective irradiance value for each of a plurality of points in the irradiance volume;
determine, for each of a plurality of reference points in the irradiance volume, a respective value for an accuracy measure, wherein the value for the accuracy measure at each reference point is representative of an accuracy with which irradiance has been determined at or near that reference point; and
perform a rendering process using the irradiance volume, wherein the rendering process is performed in dependence on the determined values for the accuracy measure, and wherein the rendering process further comprises:
rendering an image from the irradiance volume,
determining a respective pixel accuracy value for each of a plurality of pixels in the rendered image based on the determined values for the accuracy measure for the plurality of reference points,
determining, based on the pixel accuracy values, at least one lower-accuracy region of the image, and
applying a filtering process to the image, wherein the applying of the filtering process is at least partially different for the lower-accuracy region of the image than for at least one further region of the image.
2. The apparatus according to claim 1 , wherein the irradiance volume is obtained from the volumetric imaging data set using stochastic lighting simulation.
3. The apparatus according to claim 1 , wherein the rendering process further comprises determining whether to refine the image at a higher resolution based on at least some of the determined pixel accuracy values.
4. The apparatus according to claim 1 , wherein, for each pixel, the determining of the pixel accuracy value for that pixel comprises:
casting a respective sample ray into the irradiance volume; and
accumulating values for the accuracy measure along said respective sample ray to obtain the pixel accuracy value for the pixel.
5. The apparatus according to claim 4 , wherein accumulating values for the accuracy measure along said respective sample ray comprises, for each of a plurality of sample points along said respective sample ray:
determining a value for the accuracy measure at the sample point based on the values for the accuracy measure at neighboring reference points; and
calculating
Accuracy
final
=
∑
i
=
1
N
Accuracy
i
α
i
∏
j
=
0
i
-
1
(
1
-
α
j
)
where Accuracy final is the pixel accuracy value for the sample ray, N is the number of sample points on the sample ray, Accuracy i is the value for the accuracy measure at sample point i of the sample ray, and α i is a value for opacity at sample point i of the sample ray.
6. The apparatus according to claim 4 , wherein the processing circuitry is further configured to determine a color value for each pixel by accumulating color values along the sample rays.
7. The apparatus according to claim 1 , wherein the processing circuitry is configured to obtain the irradiance volume by casting a plurality of virtual photon rays into the volumetric imaging data set.
8. The apparatus according to claim 7 , wherein the determining of the values for the accuracy measure is in dependence on positions of the virtual photon rays.
9. The apparatus according to claim 8 , wherein the accuracy measure comprises a distance to a nearest one of the plurality of virtual photon rays.
10. The apparatus according to claim 8 , wherein the accuracy measure comprises a local density of virtual photon rays.
11. The apparatus according to claim 1 , wherein the applying of the filtering process to the image comprises filtering the at least one lower-accuracy region more strongly than the at least one further region.
12. The apparatus according to claim 1 , wherein the applying of the filtering process to the image comprises modifying at least one parameter of a filter such that it differs between the at least one lower-accuracy region and the at least one further region.
13. The apparatus according to claim 12 , wherein the filter comprises at least one of a diffusion filter, a bilateral filter, a non-local means filter.
14. The apparatus according to claim 1 , wherein the applying of the filtering process to the image comprises applying a diffusion filter to the image, wherein a value for a strength parameter of the diffusion filter in the at least one lower-accuracy region is different from the value for the strength parameter of the diffusion filter in the at least one further region.
15. The apparatus according to claim 1 , wherein the applying of the filtering process to the image comprises using a first filter on the at least one lower-accuracy region and using a second, different filter on the at least one further region.
16. The apparatus according to claim 1 , wherein the determining of the at least one lower-accuracy region of the image comprises processing the determined pixel accuracy values to obtain a guide image that is representative of the at least one lower-accuracy region.
17. The apparatus according to claim 16 , wherein the processing of the determined pixel accuracy values comprises thresholding the pixel accuracy values to obtain a set of lower-accuracy pixels, and dilating and/or smoothing the set of lower-accuracy pixels to obtain the guide image.
18. An image processing method comprising:
obtaining an irradiance volume representative of virtual light cast into a volumetric imaging data set, the irradiance volume comprising a respective irradiance value for each of a plurality of points in the irradiance volume;
determining, for each of a plurality of reference points in the irradiance volume, a respective value for an accuracy measure, wherein the value for the accuracy measure at each reference point is representative of an accuracy with which irradiance has been determined at or near that reference point; and
performing a rendering process using the irradiance volume, wherein the rendering process is performed in dependence on the determined values for the accuracy measure, wherein the rendering process further comprises:
rendering an image from the irradiance volume,
determining a respective pixel accuracy value for each of a plurality of pixels in the rendered image based on the determined values for the accuracy measure for the plurality of reference points,
determining, based on the pixel accuracy values, at least one lower-accuracy region of the image, and
applying a filtering process to the image, wherein the applying of the filtering process is at least partially different for the lower-accuracy region of the image than for at least one further region of the image.