This technology projects one big picture onto a cylinder using multiple projectors. Calibration is easy and we can easily project an image without misalignment or distortion.
* Currently under development
The applications of Ricoh projectors are not limited to business. Ricoh also offers projector-based signage solutions to the art and advertisement fields (Figure 1).
Figure 1 Multi projection
Projection mapping is a signage solution that uses multiple projectors to project images onto solid bodies and spaces of varied shapes.
Projection mapping requires the projectors to be calibrated beforehand. If you merely lined up multiple projectors and projected images, the images would be misaligned and deformed.
In the past, calibration for projection mapping was done by professional installers or using semi-automatic products. There were, however, many problems –special techniques and experience were needed to manually align the images and produce special content, and semi-automatic products could not handle wide-angle projections beyond 180 degrees. Solving these problems will increase projection mapping applications; no expertise will be needed to install and maintain projection mapping systems.
Cylindrical projection mapping uses multiple ultra-short-throw projectors to project a big image onto a cylinder. The image is projected as if it were appended onto the cylinder.
If you were to project an image onto a solid body of an arbitrary shape, you would need to produce special content for the shape. However, if you project an image onto a cylinder, you can use a generic rectangular image as is. Projecting an image onto the outside of a cylinder produces a 360-degree digital signage. Projecting an image onto the inside produces a wide-angle immersive display for the viewer to get submerged in.
Figure 2 Applications of cylindrical projection mapping
(Left: 360-degree digital signage, right: wide-angle immersive display)
To make cylindrical projection mapping easy, Ricoh has combined two technologies: 1) integration of separately measured 3D data and 2) distortion compensation. Calibration is semi-automatic. The combined technology simplifies the installation while enabling cylindrical projection beyond 180 degrees without misalignment or distortion.
The following describes the calibration and projection workflow to project a rectangular image onto the internal wall of a cylinder.
1) As shown in Figure 3, multiple projectors are positioned so that portions of the projected images overlap with one another.
Figure 3 Projecting calibration patterns
2) An off-the-shelf 3D sensor equipped with a camera is used to measure the shape of the cylinder. Because we must capture how the projected rays reach the cylinder, the patterns of Figure 3 are kept projected on the wall during the measurement.
From this point on, no manual work is necessary. The following steps are automatically performed using a PC.
3) It is difficult to measure the shape of the cylinder from a single point for a span of 180 degrees or wider. So the 3D sensor is moved to measure the cylinder from multiple points. The separately measured 3D data is then integrated*.
*Technology to integrate separately measured 3D data: To integrate the coordinate systems of values measured from multiple points, we need to find corresponding points between the measured values that are to be integrated. A cylinder, however, does not have any geometric feature that can be used to determine the correspondence. So patterns are projected onto the cylinder and captured by a camera from multiple points; some areas are redundant in the captures from adjacent points, and the patterns in these areas are used as groups of corresponding points. Thus, coordinates are converted.
4) To clarify the specific cylindrical shape represented by the obtained 3D measurement data, a cylindrical model is fitted to the data to estimate the shape. The estimate clarifies the size of the cylinder and its position relative to the projectors. A virtual development diagram is then generated for the inner side wall of the cylinder.
5) The development diagram of the inner side wall of the cylinder includes the patterns projected from the projectors during 3D measurement (Figure 3). Using the patterns as points of reference, the image can be corrected to eliminate distortion. The compensation process is identical to that for multi projection on a standard plane as shown in Figure 1. Specifically, brightness is adjusted where projections overlap, and the misalignment and distortions are eliminated from the image.
Figure 4 Processing of calibration and projection
Figures 3 and 5 show images projected from six Ricoh ultra-short-throw projectors onto a cylinder, 2 meters in diameter. The six projectors cover approximately 290 degrees inside the cylinder.
As shown in Figure 3, the image is significantly distorted before calibration. Figure 5 shows the result of the processing described in steps 1) to 5) above –a clear image without distortion or misalignment.
Figure 5 Result of projection
Projection using Ricoh's ultra-short-throw projectors is now possible with an angle beyond 180 degrees inside a cylinder. The 3D measurement and multi-projection technologies greatly shorten the installation time.
The scope of cylindrical projection mapping goes beyond ordinary panoramic images. It would make a good match with spherical images from the RICOH THETA camera, computer graphics (CG), and more.
Projector-based signage solutions are a fine addition to the applications of Ricoh's original technologies. Ricoh will continue to increase the value delivered to the customers in this area, too.