Method and apparatus for processing three-dimensional image data

An apparatus comprising:

• an input for receiving three-dimensional image data comprising a plurality of voxels;
• and
• processing logic, arranged:
• to apply a lower-bound-generating function to the image data to generate a lower bound for each voxel in the image data;
• to apply an upper-bound-generating function to the image data to generate an upper bound for each voxel in the image data;
• for a predetermined opacity transfer function and a predetermined viewpoint, to determine, for each voxel in the image data, whether there exists:
• (i) a value, between the lower bound and the upper bound for that voxel, at which the voxel is not completely transparent under the opacity transfer function;
• and
• (ii) a set of values for a set of sample points lying along or adjacent a viewing ray between the viewpoint and said voxel, each value of the set being between a lower bound and an upper bound for the respective sample point, according to the lower- and upper-bound-generating functions for the sample point, wherein the set of values is such that said voxel is not completely occluded from the viewpoint when the opacity transfer function is applied to the sample points along the viewing ray;
• and
• to apply a predetermined processing operation to those voxels for which both determinations are true, to generate processed image data suitable for volume rendering from the viewpoint,
• wherein the bound-generating functions and the predetermined processing operation are such that, for any three-dimensional image data, the value of a voxel after the processing operation is applied to the image data will always be between the lower bound and the upper bound given by the bound-generating functions when applied to that voxel.

A non-transitory computer-readable medium comprising software instructions which, when executed by a processing system, causes the processing system:

• to apply a lower-bound-generating function to three-dimensional image data, comprising a plurality of voxels, to generate a lower bound for each voxel in the image data;
• to apply an upper-bound-generating function to the image data to generate an upper bound for each voxel in the image data;
• for a predetermined opacity transfer function and a predetermined viewpoint, to determine, for each voxel in the image data, whether there exists:
• (i) a value, between the lower bound and the upper bound for that voxel, at which the voxel is not completely transparent under the opacity transfer function;
• and
• (ii) a set of values for a set of sample points lying along or adjacent a viewing ray between the viewpoint and said voxel, each value of the set being between a lower bound and an upper bound for the respective sample point, according to the lower- and upper-bound-generating functions for the sample point, wherein the set of values is such that said voxel is not completely occluded from the viewpoint when the opacity transfer function is applied to the sample points along the viewing ray;
• and
• to apply a predetermined processing operation to those voxels for which both determinations are true, to generate processed image data suitable for volume rendering from the viewpoint,
• wherein the bound-generating functions and the predetermined processing operation are such that, for any three-dimensional image data, the value of a voxel after the processing operation is applied to the image data will always be between the lower bound and the upper bound given by the bound-generating functions when applied to that voxel.