In conventional scanning projector display devices, such as a scanning micro-electro-mechanical system (MEMS) type projector display device, for each frame an image is scanned from left-to-right and then back from right-to-left, and so on, in a zigzag manner. This scanning technique results in limited vertical resolution on both the left and right sides of the image. More specifically, the vertical resolution on the sides is essentially half of the original vertical resolution, as can be appreciated from FIG. 1. In the example of FIG. 1, where the original horizontal by vertical resolution is 25×25 pixels, the vertical resolution at the left and right sides of the image is only 12 or 13 pixels. For another example, where the original horizontal by vertical resolution is 1280×720 pixels, the vertical resolution at the left and right sides of an image is only 360 pixels. For still another example, where original the horizontal by vertical resolution is 1366×768 pixels, the vertical resolution at the left and right sides of an image is only 384 pixels.
This reduction (halving) of the vertical resolution occurs because a scan beam is continuous when it changes its scanning direction, which has the effect of the scan beam not having even vertical spacing between the current scan line and the previous scan line. In fact, as can be appreciated from FIG. 1, the right most position of a left-to-right scan is essentially at the exact same vertical position as the right most position of the next right-to-left scan. In other words, the position at the end of one scan line is at substantially the same position that begins the next scan line. Accordingly, conventionally, for a given mechanical setup with a periodic driving scheme, there are vertical spacing gaps that will never be scanned.
FIGS. 2A and 2B illustrate an exemplary conventional MEMS driving scheme, which can be used to achieve the scanning pattern shown in FIG. 1. In FIGS. 2A and 2B, the horizontal (H) control signal is used for horizontal control of a scanning mirror. The vertical (V) control signal is used for vertical control of a scanning mirror. A single scanning mirror can be used (which is often referred to as a bi-axial mirror), in which case the H control signal and the V control signal are used to control the same mirror. Alternatively, two uni-axial scanning mirrors can be used, in which case the H control signal controls one mirror, and the V control signal controls another mirror. FIG. 2B illustrates additional details of the portions of FIG. 2A encircled by dashed oval lines.
It would be beneficial to improve the vertical resolution at the left and right sides of an image produced by a scanning MEMS type projector display device.