Projection image correction method using changing position of control point and projection system

A projection system comprising:

• a projector that displays a pattern image containing a plurality of control points on a projection surface;
• an imaging apparatus that captures images of the projection surface;
• a pointing element that irradiates the projection surface with light that satisfies a condition corresponding to a user's operation;
• and
• one or more processors,
• wherein the one or more processors each
• selects at least one of the plurality of control points as a second control point when light that satisfies a third condition and with which the projection surface is irradiated via the pointing element in a group of captured images including a plurality of captured images produced by the imaging apparatus through capture of images of the projection surface when the light which satisfies the third condition is detected in the group of captured images;
• selects the second control point as a first control point based on a position of light which satisfies a first condition and with which the projection surface is irradiated via the pointing element in the group of captured images when the light which satisfies the first condition is detected in the group of captured images,
• changes a position of the first control point based on a change in a position of light which satisfies a second condition different from the first condition and with which the projection surface is irradiated via the pointing element in the group of captured images when the light which satisfies the second condition is detected in the group of captured images, and
• displays the pattern image in which the position of the first control point is changed on the projection surface, wherein
• the second control point is a control point located at a position that is not changed based on a change in the position of the light that satisfies the second condition, and
• the first condition, the second condition, and the third condition are different from each other and each relates to irradiation condition of light projected from the pointing element.