Equatorial stitching of hemispherical images in a spherical image capture system
Hyper-hemispherical images may be combined to generate a rectangular projection of a spherical image having an equatorial stitch line along of a line of lowest distortion in the two images. First and second circular images are received representing respective hyper-hemispherical fields of view. A video processing device may project each circular image to a respective rectangular image by mapping an outer edge of the circular image to a first edge of the rectangular image and mapping a center point of the circular image to a second edge of the first rectangular image. The rectangular images may be stitched together along the edges corresponding to the outer edge of the original circular image.
1. A method of performing equatorial stitching, comprising:
capturing a first image and a second image;
mapping first pixels of the first image to a first f-theta projection based on a calibration;
mapping second pixels of the second image to a second f-theta projection based on the calibration;
offsetting a first center and a first orientation of the first f-theta projection based on the calibration;
offsetting a second center and a second orientation of the second f-theta projection based on the calibration;
back-projecting the first pixels of the first image and the second pixels of the second image to a sphere centered on a midpoint of the first f-theta projection and the second f-theta projection;
mapping the sphere to an equirectangular projection comprising an equator; and
stitching the equirectangular projection at the equator to create a stitched polar view image.
2. The method of claim 1 , where the equirectangular projection has zero distortion at the equator.
3. The method of claim 1 , further comprising equidistant feathering.
4. The method of claim 1 , where mapping the sphere to the equirectangular projection comprises:
mapping the first center to a top edge of the equirectangular projection; and
mapping the second center to a bottom edge of the equirectangular projection.
5. The method of claim 1 , where mapping the sphere to the equirectangular projection comprises:
mapping a first outer edge of the first f-theta projection to the equator of the equirectangular projection; and
mapping a second outer edge of the second f-theta projection to the equator of the equirectangular projection.
6. The method of claim 1 , further comprising:
dividing the stitched polar view image into a first portion and a second portion;
rotating the first portion and the second portion; and
combining the first portion and the second portion to generate a stitched equatorial view image.
7. An imaging apparatus configured to equatorial stitching, the imaging apparatus comprising:
a processor;
a first camera facing a first direction;
a second camera facing a second direction different from the first direction; and
a non-transitory computer-readable apparatus comprising computer instructions, the computer instructions configured to, when executed by the processor, cause the imaging apparatus to:
capture a first image via the first camera and a second image via the second camera;
map the first image to a first f-theta projection and the second image to a second f-theta projection;
offset a first center and a first orientation of the first f-theta projection and a second center and a second orientation of the second f-theta projection;
back-project the first image and the second image to a sphere centered on a midpoint of the first f-theta projection and the second f-theta projection;
map the sphere to an equirectangular projection comprising an equator; and
stitch the equirectangular projection at the equator to create a stitched polar view image.
8. The imaging apparatus of claim 7 , where the first camera is a front facing hyper-hemispherical camera, the second camera is a back facing hyper-hemispherical camera, and the first camera and the second camera overlap along a meridian line.
9. The imaging apparatus of claim 8 , where the first center and the first orientation are offset from the second center and the second orientation based on a physical disparity between the first camera and the second camera.
10. The imaging apparatus of claim 8 , where the first camera and the second camera comprise video cameras, and where the stitched polar view image is part of a spherical video.
11. The imaging apparatus of claim 7 , where the non-transitory computer-readable apparatus further comprises computer instructions configured to, when executed by the processor, cause the imaging apparatus to:
divide the stitched polar view image into a first portion and a second portion;
rotate the first portion and the second portion; and
combine the first portion and the second portion to generate a stitched equatorial view image.
12. The imaging apparatus of claim 7 , where the computer instructions configured to cause the imaging apparatus to map the first image to the first f-theta projection and the second image to the second f-theta projection comprise computer instructions that cause the imaging apparatus to:
map a first outer edge of the first f-theta projection to the equator of the equirectangular projection; and
map a second outer edge of the second f-theta projection to the equator of the equirectangular projection.
13. The imaging apparatus of claim 7 , where the computer instructions configured to cause the imaging apparatus to stitch the equirectangular projection at the equator performs a conventional stitching algorithm designed for rectangular images.
14. A non-transitory computer-readable medium comprising one or more instructions which, when executed by a processor, causes the processor to:
map a first image to a first f-theta projection and a second image to a second f-theta projection;
offset a first center and a first orientation of the first f-theta projection and a second center and a second orientation of the second f-theta projection;
back-project the first image and the second image to a sphere centered on a midpoint of the first f-theta projection and the second f-theta projection;
map the sphere to an equirectangular projection comprising an equator; and
stitch the equirectangular projection at the equator to create a stitched polar view image.
15. The non-transitory computer-readable medium of claim 14 , where the one or more instructions configured to cause the processor to stitch the equirectangular projection at the equator performs a conventional stitching algorithm designed for rectangular images.
16. The non-transitory computer-readable medium of claim 14 , where the one or more instructions configured to cause the processor to stitch the equirectangular projection are not sphere-aware.
17. The non-transitory computer-readable medium of claim 14 , where the one or more instructions are further configured to cause the processor to convert the stitched polar view image to a stitched equatorial view image.
18. The non-transitory computer-readable medium of claim 14 , where the one or more instructions configured to cause the processor to map the first image to the first f-theta projection and the second image to the second f-theta projection comprise computer instructions that cause the processor to:
map the first center to a top edge of the equirectangular projection; and
map the second center to a bottom edge of the equirectangular projection.
19. The non-transitory computer-readable medium of claim 18 , where the one or more instructions configured to cause the processor to map the first image to the first f-theta projection and the second image to the second f-theta projection comprise computer instructions that cause the processor to:
map a first outer edge of the first f-theta projection to the equator of the equirectangular projection; and
map a second outer edge of the second f-theta projection to the equator of the equirectangular projection.