Method for calibrating a stereoscopic photography device
View Patent ↗The present invention concerns the field of stereoscopic photography devices and more precisely calibration thereof. The invention proposes a method for calibrating a stereoscopic photography device that calculates a set of correction parameters for the images. These parameters are classed according to an order of importance. The first-order correction parameters are estimated first, the second-order correction parameters secondly. Advantageously, the first-order parameters are refined by taking account of the estimation values of the second-order parameters. Advantageously, a measurement of the relevance of the scene is carried out before the actual calibration.
1. Calibration method for calibrating a stereoscopic photography device having a right camera for capturing a right-hand image and a left camera for capturing a left-hand image, at least four orders from lowest to highest of defects appearing between the right and left hand images, the defects comprising at least a global translation offset of the image, a horizontal and vertical trapezium deformation, a rotation, and a zoom factor, each of these defects being able to be corrected by applying a transformation to at least one of the two captured images, the method comprising the steps of:
calculating a relevance index to determine a scene for implementing the calibration method, and for the determined scene performing the following:
a) estimating the correction parameters for the defects of at least one lower order;
b) estimating the correction parameters for the defects of a higher order using the estimated correction parameters for the defects of the at least one lower order;
c) re-estimating the correction parameters for the defects of the at least one lower order using the estimated correction parameters for the defects of the higher order;
d) re-estimating the correction parameters for the defects of the higher order using the re-estimated correction parameters for the defects of the at least one lower order; and
e) estimating the correction parameters for the defects of a next higher order using the re-estimated correction parameters for the at least two lower orders.
2. Calibration method according to claim 1 , further comprising a fifth order of defects to be corrected of
a barrel or pincushion distortion.
3. Calibration method according to claim 1 , characterized in that the calculation of an index of relevance of the scene comprises the steps of:
calculating histograms of the right and left images, each histogram comprising a spread relating to the level of detail of a scene;
calculating, for each area of the plurality of areas of the left and right images, a parallax index and a correlation reliability index;
calculating, from the spreads of the histograms and from the correlation reliability indices, a detail index of the scene;
calculating, from the parallax indices, a distance index that will be greater, the more the parallax indices are uniformly low; and
calculating, from the detail index and the distance index the relevance index.
4. Calibration method according to claim 1 , further comprising a step of repeating steps c) and d) until convergence of the estimation of the parameters is obtained, before proceeding to step e).
5. Calibration method according to claim 1 , further comprising a step of displaying the calculated relevance index on a screen of the device.
6. Calibration method according to claim 5 , wherein the relevance index is a relevance bar the length of which is proportional to the relevance index.
7. Calibration method according to claim 6 , wherein the color of the bar is used to determine zones for the relevance index.