CORRECTION OF A PROJECTED IMAGE BASED ON A REFLECTED IMAGE
 Image projection systems may be used to enlarge a still or video image, or to enable the image to be viewed simultaneously by a large or small audience. As both projection devices and the personal computers used to drive them have become increasingly smaller and more portable, it has become possible to give sophisticated visual presentations in venues that were previously inaccessible.
 Unfortunately, although modern projection equipment may now require only a power socket, many rooms may lack a suitable projection surface. Bringing along a projection screen, however, may compromise the portability of modern projection apparatus. The alternative, projection of an image onto even a lightly colored wall, may detract from the content of the presentation. A projection system that actively compensates for the color characteristics of a projection surface thus would be desirable.
 A method is provided, including providing image data for a desired image, projecting the desired image onto a surface to produce a reflected image, comparing the reflected image to the image data to determine an observed difference, and modifying the projected image to reduce the observed difference.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is an isometric view of a display system according to an embodiment of the invention.
 FIG. 2 is a schematic representation of the display system of FIG. 1.
 FIG. 3 is a flowchart depicting a method of colorcorrecting a projected image, according to an embodiment of the invention.
 Referring initially to FIG. 1, a display system according to an embodiment of the present invention is shown generally at 10. Specifically, FIG. 1 illustrates a display system including a projector 12 adapted to produce an image 14 on a display surface 16. Projector 12 typically is associated with a source of image data, depicted in FIG. 1 as a laptop computer 18. Projector 12 thus may be configured to project an image 14 derived from the image data received from computer 18 onto display surface 16.
 The projector may take the form of a digital projector, or any other suitable projection device. It should be appreciated that many types of projection systems may be suitable for the purposes of this disclosure. The projector itself may include, but is not limited to, digital overhead projectors, active liquid crystal display (LCD) projection devices, and micromirror-based projection devices. The images projected by the image projector may include still images or video images. Both still and video images will be referred to herein simply as projected images.
 Projector 12 typically includes a light engine 20. Light engine 20 is typically configured to direct and transmit
light to display surface 16 so as to generate a projected image that is derived from, and therefore generally corresponds to, the image data received from computer 18. Light engine 20 may include any suitable illumination source adapted to optically address display surface 16, including single white light sources (such as a mercury lamp, plasma lamp, incandescent lamp, etc.) and/or multiple white or single color light sources (such as light emitting diodes (LEDs), laser diodes, etc.). Additionally, projector 12 may include optics, spatial light modulators, scanning mirrors, focusing devices, color-generation devices, controllers, etc. which may accommodate production of a multi-color image on the display surface.
 As depicted schematically in FIG. 2, display system 10 may also include a processor 22 that is configured to receive the image data from image data source and to convert the image data into commands appropriate for driving light engine 20. Processor 22 may be included with projector 12, as shown, or may be an independent processor that is associated with the projector. Processor 22 may be in communication with a memory 24 that serves as temporary (or long term) storage of data such as calibration information, color information, and other data needed by processor 22 to operate projector 12.
 The image data source 18 may be, without limitation, a personal computer, such as a notebook computer, a personal digital assistant, or a mainframe computer such as a file server. The data connection between the image data source and the projector processor may include a hardwire connection, or may be a wireless data connection. Where the data connection is a hardwire connection, the hardwire connection may be a cable, in a local area network or a large area network. Alternatively, the data connection may include a wireless connection that utilizes modulated radiation, typically an infrared or rf (radio frequency) signal. Alternatively, projector 12 may create the projected image from image data stored internally by the projector, for example, using memory 24, so that connection to an external data source is unnecessary. Similarly, projector 12 may include a disk drive or other auxiliary memory device, enabling image data to be received by processor 22 directly.
 In response to commands from the processor, light engine 20 typically directs and transmits visible light in the form of a projected image 26 to display surface 16 to produce reflected image 28, where reflected image 28 nominally is related to the projected image as a mirror image. Such relationship assumes, however, that light engine 20 perfectly produces the color characteristics defined by the image data received by the projector, and that display surface 16 provides a perfectly neutral and reflective display surface. This may not necessarily be the case in every instance.
 Color characteristics, as used herein, may include the hue, intensity, and brightness of all or a portion of an image. Such color characteristics may be represented and accurately defined with reference to the coordinates of a particular color space. A color space is typically a mathematical construction that permits color information to be described numerically and/or plotted graphically. Various color spaces may reference color values such as hue, lightness, brightness, value, reflectance, vividness, saturation, or chroma, among others.