# US 9,039,194 B2 · Method and device for controlling a video projector in a video projection system comprising multiple video projectors > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,039,194 B2 - Document ID: US9039194B2 - Status: Granted - Kind: B2 - Application number: 13/722,745 - Filed: 2012-12-20 - Published: 2013-07-04 - Granted: 2015-05-26 - Earliest claimed: 2011-12-22 - Assignees: Canon Kabushiki Kaisha - Applicants: Canon Kabushiki Kaisha - Inventors: Falk Tannhäuser; Pascal Rousseau - Web page: https://patentgrep.com/patent/US9039194B2 ## CPC - H04N 9/3194: {including sensor feedback} - H04N 9/3147: {Multi-projection systems (video walls G06F3/1446)} - H04N 9/3188: {Scale or resolution adjustment (scaling in general G06T3/40; resolution modifying circuits for displays in general G09G5/391)} - G03B 21/147: {Optical correction of image distortions, e.g. keystone} - G03B 33/10: Simultaneous recording or projection (G03B33/02, G03B33/04 G03B33/06 take precedence) - H04N 9/3185: {Geometric adjustment, e.g. keystone or convergence (optical or mechanical adjustment of convergence H04N9/317; using scanning means H04N3/22; optical or mechanical adjustments of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/14)} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION - G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D) ## Abstract Controlling at least one video projector of a video projection system comprising multiple video projectors having a modifiable focal length and adapted to project sub-images. After determining a first calibration parameter associated with a first predetermined focal length of the video projectors, a second calibration parameter corresponding to a second predetermined focal length of the video projectors is computed, the second calibration parameter computed as a function of the first calibration parameter and the second predetermined focal length different from the first one. A display parameter is computed for a video projector, the display parameter being computed as a function of second calibration parameter, and a sub-image to be projected by the video projector is calculated according to the computed display parameter. Necessary display parameters are determined during an initial calibration step and used during a projection session whenever the user issues an “optical zoom” command, without repeating the calibration. ## Claims ### Claim 1 A method for controlling at least one video projector in a video projection system comprising multiple video projectors amongst which is the at least one video projector, each of the video projectors of the video projection system having a modifiable focal length and being adapted to project sub-images of the images to be projected by the video projection system, the method comprising: determining at least one first calibration parameter associated with a first predetermined focal length of the video projectors; computing at least one second calibration parameter corresponding to a second predetermined focal length of the video projectors, the at least one second calibration parameter being computed as a function of the at least one first calibration parameter, the second predetermined focal length being different from the first predetermined focal length; computing at least one display parameter for at least the at least one video projector, the at least one display parameter being computed as a function of the at least one second calibration parameter; and calculating at least one sub-image to be projected by the at least one video projector, according to the at least one computed display parameter. ### Claim 2 (depends on 1) The method of claim 1, wherein the at least one first and second calibration parameters comprise positions of predetermined points of sub-images projected by video projectors of a set of the video projectors, the set of video projectors comprising the at least one video projector and wherein the at least one display parameter relates to a projection position of a sub-image to be projected by the at least one video projector. ### Claim 3 (depends on 2) The method of claim 2, wherein the step of determining at least one first calibration parameter comprises a step of analysing a picture representing sub-images projected by the video projectors of the set of video projectors. ### Claim 4 (depends on 1) The method of claim 1, wherein the step of computing at least one display parameter uses a keystone distortion correction algorithm. ### Claim 5 (depends on 1) The method of claim 1, wherein the step of computing at least one display parameter comprises the two determining steps of determining at least one sub-image that is to be projected by the at least one video projector and determining the projection position of the at least one sub-image that is to be projected by the at least one video projector, wherein the two determining steps are based upon the at least one second calibration parameter. ### Claim 6 (depends on 5) The method of claim 5, wherein the at least one display parameter comprises parameters of partitioning, re-scaling, and geometric distortion correction of images to be displayed by the video projection system for each of the video projectors of the video projection system. ### Claim 7 (depends on 1) The method of claim 1, wherein the step of computing at least one display parameter further comprises a step of determining at least one blending area in a projection area associated with the at least one video projector, common to projection areas associated with other video projectors of the video projection system, so that the luminance of pixels projected in the at least one blending area is constant. ### Claim 8 (depends on 1) The method of claim 1, wherein the first predetermined focal length of the video projectors is the minimum focal length of the projectors' zoom lenses. ### Claim 9 (depends on 1) The method of claim 1, wherein the at least one first calibration parameter is determined for at least two distinct calibration focal lengths. ### Claim 10 (depends on 9) The method of claim 9, wherein the at least two distinct calibration focal lengths comprise the minimum and maximum focal lengths of the projectors' zoom lenses. ### Claim 11 (depends on 1) The method of claim 1, wherein the step of calculating at least one sub-image to be projected by the at least one video projector comprises a step of up-scaling a part of an image to be projected by the video projection system, interpolating points of the part of the image, and down-scaling the part of the image. ### Claim 12 (depends on 1) A non-transitory computer readable medium having stored thereon a program that causes an apparatus to execute the method according to claim 1. ### Claim 13 An apparatus for controlling at least one video projector in a video projection system comprising multiple video projectors amongst which is the at least one video projector, each of the video projectors of the video projection system having a modifiable focal length and being adapted to project sub-images of the images to be projected by the video projection system, the apparatus comprising at least one microprocessor configured for carrying out the steps of, determining at least one first calibration parameter associated with a first predetermined focal length of the video projectors; computing at least one second calibration parameter corresponding to a second predetermined focal length of the video projectors, the at least one second calibration parameter being computed as a function of the at least one first calibration parameter and the second predetermined focal length being different from the first predetermined focal length; computing at least one display parameter for the at least one video projector, the at least one display parameter being computed as a function of the at least one second calibration parameter; and calculating at least one sub-image to be projected by the at least one video projector according to the at least one computed display parameter. ### Claim 14 (depends on 13) The apparatus of claim 13, wherein at least one of the at least one microprocessor is common to a plurality of video projectors of the video projection system. ### Claim 15 (depends on 13) The apparatus of claim 13, wherein at least one of the at least one microprocessor is dedicated to one of the video projectors of the video projection system. ### Claim 16 (depends on 13) The apparatus of claim 13 wherein the at least one microprocessor is further configured for carrying out a step of analysing a picture representing sub-images projected by the video projectors of the set of video projectors when carrying out the step of determining at least one first calibration parameter. ### Claim 17 (depends on 13) The apparatus of claim 13 wherein the at least one microprocessor is further configured for implementing a keystone distortion correction algorithm when carrying out the step of computing at least one display parameter. ### Claim 18 (depends on 13) The apparatus of claim 13 wherein the at least one microprocessor is further configured for carrying out determining steps of determining at least one sub-image that is to be projected by the at least one video projector and determining the projection position of the at least one sub-image that is to be projected by the at least one video projector, when computing at least one display parameter, wherein the two determining steps are based upon the at least one second calibration parameter. ### Claim 19 (depends on 13) The apparatus of claim 13 wherein the at least one microprocessor is further configured for carrying out a step of determining at least one blending area in a projection area associated with the at least one video projector, common to projection areas associated with other video projectors of the video projection system, when carrying out the step of computing at least one display parameter, so that the luminance of pixels projected in the at least one blending area is constant. ### Claim 20 (depends on 13) The apparatus of claim 13 wherein the at least one microprocessor is further configured for carrying out a step of up-scaling a part of an image to be projected by the video projection system, interpolating points of the part of the image, and down-scaling the part of the image, when carrying out the step of calculating at least one sub-image to be projected by the at least one video projector.