Background correction for birefringence measurements

A computer system, comprising:

• a logic subsystem;
• and
• a storage subsystem comprising instructions executable by the logic subsystem to read birefringent data from a storage medium by
• receiving an image of a voxel of the storage medium, the image comprising higher frequency image information arising from a birefringence state of the voxel and lower frequency image information arising from one or more birefringent regions of the storage medium other than the voxel;
• applying a first low-pass filter with a first cutoff frequency to the image of the voxel to obtain a first background image;
• applying a second low-pass filter with a second cutoff frequency to the image of the voxel to obtain a second background image, the second cutoff frequency being different than the first cutoff frequency;
• determining an enhanced background image from the first background image and the second background image;
• determining birefringence values for the enhanced background image;
• determining birefringence values for the image of the voxel;
• and
• correcting the birefringence values for the image of the voxel based upon the birefringence values for the enhanced background image.

A computer-readable storage device comprising instructions that are executable by a computing system to read birefringent data from a storage medium by

• receiving an image of a voxel of the storage medium, the image comprising higher frequency image information arising from a birefringence state of the voxel and lower frequency image information arising from one or more birefringent regions of the storage medium other than the voxel;
• applying a first low-pass filter with a first cutoff frequency to the image of the voxel to obtain a first background image;
• applying a second low-pass filter with a second cutoff frequency to the image of the voxel to obtain a second background image, the second cutoff frequency being different than the first cutoff frequency;
• determining an enhanced background image from the first background image and the second background image;
• determining birefringence values for the enhanced background image;
• determining birefringence values for the image of the voxel;
• and
• correcting the birefringence values for the image of the voxel based upon the birefringence values for the enhanced background image.