fig2 is a block diagram of a conventional computer video subsystem . fig3 a and 3b are perspective and side views , respectively , of a laptop computer with a rear projection display . fig4 is a schematic view of a standard three cell image projector . fig5 a and 5b are perspective and side views , respectively , of a laptop computer with a rear projection display . fig6 a , 6 b , and 7 are side views of laptop computers with projection displays . fig8 a and 8b are perspective views of self contained computers each with a single housing and a projection display . referring to fig3 a and 3b , image projection is used to improve the display qualities of a computer 40 , including but not limited to a portable ( e . g ., laptop ) computer or any other self - contained computer ( i . e ., a computer in which the central processor and the display reside in a common housing or in attached housings ). instead of an lcd panel and the accompanying electronics , the computer 40 includes a base housing 44 containing an image projection engine 42 ( as well as a microprocessor 43 and an alphanumeric input device , such as a keyboard 47 ) and a lid 45 comprising a rear projection screen 46 and a reflective flap 48 . the projection engine 42 projects an image beam 49 containing an image 50 onto the reflective flap 48 , which in turn reflects the beam 49 toward the screen 46 . when the beam 49 impinges upon the screen 46 , the screen 46 transmits the image 50 toward the user . to insure that the image 50 is directed toward the user 52 regardless of the angle at which the beam 49 hits the screen 46 , the screen 46 must be an angle transforming screen , such as the microsharp ™ screen made by nashua corporation , which is used to produce wide angle viewing screens . the reflective flap 48 includes a body 54 , which is made of a relatively rigid material such as hard plastic to protect the screen when the lid 45 is closed , and a reflective layer 56 , such as a mirror or other optically reflective material , that covers the front surface 55 of the body 54 . the reflective layer 56 may be attached to the body 54 by any suitable means , such as an adhesive glue . the flap 48 is mounted to the screen 46 by a hinge 58 that spans most of the width w of the screen 46 or , alternatively , by multiple hinges ( not shown ) distributed across the width w of the screen 46 . preferably , the flap 48 is detachable from the lid 45 so that the image 50 may be displayed on a wall 64 ( fig3 b ) or any other surface that is not attached to and / or is distant from the computer 40 . likewise , the lid 45 is mounted to the base 44 by hinges 62 a , 62 b . when the lid 45 is fully opened , the screen 46 and the reflective flap 48 must mechanically articulate such that the optical path from the projection engine 42 to the screen 46 keeps the image 50 on the screen 46 , in focus , and properly sized . this may be accomplished , e . g ., by using hinges with mechanical stops that lock the hinges 58 , 62 a , 62 b when the lid 45 is fully opened . for the reflective flap 48 , a releasable latch 60 may be used in lieu of or in addition to the locking hinge 58 to control the position of the flap 48 . when the screen 46 and the flap 48 are positioned properly , the image 50 fills essentially all of the screen &# 39 ; s surface ( e . g ., between 90 % and 100 % of the surface ). referring to fig4 the projection engine 42 is a standard three cell , color , lcd projector reduced to a scale small enough for portable applications . for a laptop computer , the dimensions of the projection engine should be approximately 1 . 0 ″× 1 . 0 ″× 2 . 5 ″ but may differ depending upon the application . light in the projection engine is generated by a light source 66 that emits a light beam 67 having wavelengths in at least the red , green , and blue ranges . a light source that produces light ranging from infrared to ultraviolet wavelengths also may be used . when light is emitted from the source 66 , the light passes through a polarizer 68 , which polarizes the light at each wavelength to the angle required by the lcd cells ( discussed below ) in the projection engine 42 . the required polarization angle depends upon the types of lcd cells ( light valves ) used . the polarized light then encounters a series of dielectric coated optical devices 70 a - 70 c that act as reflective bandpass filters ( i . e ., each device reflects substantially all light in a given frequency band and transmits substantially all other light ). the first filter 70 a , which reflects red light and transmits substantially all other wavelengths , is positioned to direct red light toward a first light valve 72 a , described below . likewise , the second filter 70 b reflects substantially all green light toward a second light valve 72 b and transmits substantially all other light . the third filter 70 c in turn reflects substantially all remaining blue light toward a third light valve 72 c . after the red , green , and blue wavelengths are separated , the light in each range is filtered by the corresponding light valve 72 a - 72 c . each light valve 72 a - 72 c is a standard transmissive lcd cell scaled to a size small enough for portable applications ( e . g ., typically having approximately a 1 . 3 ″ diagonal ). each lcd cell 72 a - 72 c comprises an array of pixels ( e . g ., 800 × 600 pixels , 1024 × 768 pixels , etc .) controlled by a video subsystem that includes a standard color lcd controller 74 . as light of each color passes through the corresponding light valve 72 a 72 c , the lcd controller 74 alters the properties of the liquid crystal elements at each pixel to appropriately attenuate the magnitude of the corresponding color at the pixel . the light emerging from the light valves 72 a - 72 c then encounters a second set of reflective bandpass filters 76 a - 76 c that recombine the filtered light into a single image beam 78 . the color and brightness of the image 78 at each pixel is determined by the combined output of the light valves 72 a - 72 c at the pixel . before the image leaves the projection engine 42 , it typically passes through magnifying optics 80 . the required magnification value of the optics 80 is determined by three factors : 1 ) the size of the lcd cells in the projection engine , 2 ) the surface area of the screen , and 3 ) the optical path length between the projection engine and the screen ( i . e ., the distance from the engine to the flap plus the distance from the flap to the screen ). as described above , the lens must magnify the image at a rate that allows the image to fill all or nearly all of the screen ( see fig3 a and 3 b ). in addition , the projection engine 42 must project the image so that it is properly aligned with the screen . distortion correction optics ( e . g ., keystone optics ) may be used correct distortions in the image . projection engines other than a standard three cell engine also may be used . for example , the image projector may be a standard reflective polymer dispersed liquid crystal ( pdlc ) engine , a single filter sub - pixelated lcd engine , a single filter sub - pixelated engine with a color separator , or a color stack engine ( i . e ., a subtractive color system ), all of which are known in the art . referring to fig5 a and 5b , a mirror 82 may be used instead of a reflective flap to reflect images onto the screen 84 of a portable computer 81 . a projection engine 86 in the base 88 of the computer 81 projects an image 90 toward the mirror 82 . the mirror 82 in turn reflects the image 90 toward the screen 84 . if the mirror 82 has optical power ( i . e ., is a rounded or magnifying mirror ), it may magnify the image 90 to fill essentially all of the screen . the required magnification and thus the mirror &# 39 ; s shape are determined by four factors : 1 ) the size of the lcd cells in the projection engine , 2 ) the surface area of the screen , 3 ) the optical path length from the mirror to the screen , and 4 ) the magnification rate of other power elements that may be in the optical path . the magnifying mirror 82 mounts to a retractable tray 92 that slides through a slot 93 in the base 88 of the computer 81 . the slot 93 is wider than the tray so that teeth 94 a , 94 b may protrude from the tray 92 . when the tray 92 is fully extended , the teeth 94 a , 94 b abut the rear wall 96 of the computer 81 to prevent the tray 92 from exiting the base 88 entirely . the projection engine 86 , which is housed in the base 88 of the computer 81 , projects light through an opening 98 in the rear wall 96 toward the mirror 82 when the tray 92 is extended . when the tray 92 retracts into the base 88 , the mirror 82 enters the opening 98 and occupies the space between the projection engine 86 and the rear wall 96 . a back panel 100 of the tray 92 closes the opening 98 and protects the mirror 82 when the tray 92 is in this position . referring to fig6 a and 6b , front projection may be used instead of rear projection to display computer - generated images . in fig6 a , a projection engine 112 located in the base 114 of a laptop computer 110 projects an image beam 116 through an opening 117 in the base 114 and directly onto the front surface 118 of the screen 120 . the screen 120 , which consists of any suitable reflection - type , refracting material , reflects the image toward the user 122 . the projection engine 112 must magnify the image 116 rapidly enough to fill essentially all of the front surface 118 of the screen 120 , as discussed above . in addition , the screen 120 should be mounted to the base 114 by a locking hinge 124 to ensure that while the computer is in use , the screen 120 remains at a proper angle to allow the image 116 to fill essentially all of the screen 120 and to prevent any of the image 116 from missing the screen 120 entirely . distortion correcting optics ( e . g ., keystone optics ) may be used to correct distortions that may occur in the image 116 . in fig6 b , the projection engine 112 initially projects the image beam 116 away from the screen 120 and toward a reflective surface 126 , such as a mirror . the mirror 126 in turn reflects the image beam 116 through the opening 117 in the base and onto the front surface 118 of the screen 120 . again , a locking hinge 124 should mount the screen 120 to the base 114 and the magnification rate of the projection engine 112 should be sufficiently large to allow the image to fill essentially all of the front surface 118 of the screen 120 . if the mirror 126 is an optical power element ( e . g ., a magnifying mirror ), the mirror itself may magnify the image to fill essentially all of the screen &# 39 ; s surface 118 . referring to fig7 a self - contained display assembly 130 mounted by a locking hinge 131 to a laptop computer 132 serves as a lid to the computer 132 . the display assembly 130 includes a screen 134 and a projection engine 136 mounted against an edge of the screen . the projection engine 136 receives image data from the computer 132 through a cable 138 that runs along one side of the screen 134 and terminates at a connector 140 that attaches to the computer 132 . a retractable tray 142 that extends from the computer 132 holds a magnifying mirror 144 . when the locking hinge 131 holds the display assembly 130 in the fully - opened position , the projection engine 136 projects an image beam 146 toward the magnifying mirror 144 . the magnifying mirror 144 in turn reflects the image 146 onto the rear surface 148 of the screen 134 , magnifying the image 146 to fill essentially all of the screen 134 . when the computer 132 is not in use , the tray 142 may be pushed into the computer 132 to protect the magnifying mirror 144 . if the hinge 131 is a detachable hinge , the display assembly 130 may be removed from the computer 132 and used with another computer system . referring to fig8 a and 8b , image projection may be used in - a self - contained computer 150 having a microprocessor 152 , a keyboard 154 , an image projector 156 , and a screen 158 all in a common housing . preferably , the projector has a resolution of at least 800 × 600 pixels and is approximately 1 . 5 ″ high , 4 ″ wide , and 5 ″ long . in fig8 a , the image projector 156 projects an image beam 160 toward a reflective surface 162 , which in turns reflects the image beam 160 onto a rear projection screen . in fig8 b , the image projector 156 projects the image beam 160 directly onto the front surface of a front projection screen . other embodiments are within the scope of the following claims . for example , the light source in the projection engine of fig4 may use color lasers .