Optical system and display device using the same

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a device for displaying a large-sized image, and more particularly, to a display device in which the optical efficiency is enhanced by using a color drum.

[0003] 2. Description of the Related Art

[0004] Recently, a flat panel display that has thin and large-sized screen attainment characteristics attracts public attention, and is anticipated to replace the conventional cathode ray tube (CRT) that has a limitation in the screen size and a large volume. As such a flat panel display, there are a liquid crystal display (LCD), a plasma display panel (PDP), a projector and the like. Among these flat panel displays, the projector that magnifies a small-sized image made by an LCD and projects the magnified image to a large-sized screen through a projection lens stands in the spotlight as a new large-sized screen display.

[0005] The projector includes a lamp system for generating light, an optical system for converging the generated light, an image display device for displaying the converged light as colors according to an inputted electric signal, and a projection system for magnifying and projecting the displayed colors. Here, the image display devices are classified into a transmission type image display device for transmitting an incident light according to an inputted electric signal and a reflection type image display device for reflecting the incident light according to the inputted electric signal. The LCD having an advantage of the slimness is mainly used as the image display device.

[0006] Recently, as a small-sized image display device is developed, various kinds of projectors are being commercialized. The projectors are generally classified into single panel type using one sheet of image display device, double panel type using two sheets of image display devices and triple panel type using three sheets of image display devices. The single panel type projector that uses one sheet of image display device to display images is currently widely used in aspects of cost and structure.

[0007] The single panel type projector can use any one of three ways to express the white color: a first way in which R, G and B color filters are attached to the image display device to express the white color, a second way in which micro lenses are attached to the image display device to split R, G and B color lights in different directions and to express the white color, and a third way in which color wheels are utilized to transmit R, G and B color lights selectively one after another in time order.

[0008]FIG. 1 illustrates a conventional projector in which color filters are attached to the image display device and FIG. 2 illustrates a conventional projector in which a micro lens is attached to the image display device.

[0009] Referring to FIG. 1, in an image display device <b>120</b>, R, G and B pixels <b>122</b> are linearly arranged and a filter <b>124</b> is attached to each pixel <b>122</b>. Light generated by a lamp system <b>100</b> is converged by an optical system <b>110</b> and incident into the image display device <b>120</b>. Here, the image display device <b>120</b> expresses the incident light as colors according to inputted electric signals. Accordingly, the converged light is expressed as colors depending on the electric signal inputted to each pixel <b>122</b> of the image display device <b>120</b>, and transmits the filter <b>124</b> or is reflected by the filters <b>124</b>. The transmitted colors are magnified and outputted onto a screen <b>140</b> by a projection lens <b>130</b>.

[0010] In such a way, however, since three pixels (R, G, B) express one white light, the total number of pixels on the image display device <b>120</b> express the white color of which the resolution is reduced to one third (⅓). Like this, since so large area is required to express one white color, the resolution is lowered. In addition, since the filters <b>124</b> attached to the image display device <b>120</b> do not have good transmission characteristics, they lower the optical efficiency.

[0011] As an alternative proposal, referring to FIG. 2, micro lenses <b>165</b> each of which corresponds to three pixels <b>161</b>, <b>162</b> and <b>163</b> of R, G and B are arranged on an image display device <b>160</b>. Separate R, G and B reflection mirrors <b>152</b>, <b>154</b> and <b>156</b> are provided between the optical system <b>110</b> and the image display device <b>160</b> in order to split the light and apply the split lights to the pixels <b>161</b>, <b>162</b> and <b>163</b> at specific angles respectively. Accordingly, the light generated by the lamp system <b>100</b> passes the optical system <b>110</b>, is split into color lights by the reflection mirrors <b>152</b>, <b>154</b> and <b>156</b>, and is then incident into the image display device <b>160</b> at different angles depending on the slopes of the reflection mirrors <b>152</b>, <b>154</b> and <b>156</b>. The image display device <b>160</b> receives the lights inputted from the reflection mirrors <b>152</b>, <b>154</b> and <b>156</b> through the micro lenses <b>165</b> and sends them to corresponding pixels <b>161</b>, <b>162</b> and <b>163</b> to express colors according to the inputted electric signal.

[0012] However, even in such a way, since three pixels express one white color like the way in which filters are attached to the image display device (shown in FIG. 1), the resolution is lowered.

[0013] To solve the lowering problem in the resolution appearing in the ways of FIGS. 1 and 2, a way shown in FIG. 3 has been suggested.

[0014]FIG. 3 illustrates a conventional projector using a color wheel.

[0015] Referring to FIG. 3, an image display device <b>180</b> includes white pixels <b>182</b>, <b>183</b> and <b>184</b> arranged to express one white color by one pixel and a color wheel <b>170</b> between a lamp system <b>100</b> and an optical system <b>110</b>. The color wheel <b>170</b> has R, G and B transmission filters <b>174</b><i>a, </i><b>174</b><i>b </i>and <b>174</b><i>c </i>arranged on predetermined areas of a rotation disk.

[0016] As the light generated by the lamp system <b>100</b> is incident into the color wheel <b>170</b>, the color wheel <b>170</b> is rotated by a motor <b>172</b> to split the incident light into color lights sequentially and transmit the split color lights to the optical system <b>110</b>. Then, the optical system <b>110</b> converges the split color lights to one white pixel of the image display device <b>180</b> to express a white color.

[0017] Since the above method can express one white color by one white pixel, the resolution is enhanced by three times compared with the related arts shown in FIGS. 1 and 2 but the brightness is contrary decreased to one third (⅓). This is because the color wheel <b>170</b> transmits only the corresponding lights of the respective transmission filter <b>174</b><i>a, </i><b>174</b><i>b </i>and <b>174</b><i>c </i>and the remaining light is not transmitted but lost to decrease the amount of light so. Accordingly, the light efficiency is decreased.

[0018] According to the way described above, the resolution is good but the brightness is bad. To this end, there is being developed a technology which is based on the way shown in FIG. 3 and in which the light reflected from the color wheel and lost is reused to enhance the light efficiency.

[0019]FIG. 4 illustrates a conventional projector provided with a road lens.

[0020] Referring to FIG. 4, a conventional projector includes a lamp system <b>210</b> for generating light, a road lens <b>220</b> shaped in a rectangular, for receiving the light generated from the lamp system <b>210</b>, totally reflecting and outputting the generated light, and totally reflecting and outputting the re-inputted light, a color wheel <b>230</b> for selectively transmitting the light outputted from the road lens <b>220</b>, a converging lens <b>240</b> for converging the transmitted light from the color wheel <b>230</b>, an image display device <b>250</b> for expressing the converged light in colors, and a projection lens for magnifying and projecting the colors expressed by the projection lens <b>250</b> onto a screen <b>270</b>.

[0021] The lamp system <b>210</b> includes a light source <b>212</b> for generating the light and an elliptic reflecting mirror <b>214</b> for controlling the generated light to be inputted to the road lens <b>220</b>. Accordingly, all the light generated by the converging lens <b>210</b> is incident into the road lens <b>220</b>.

[0022] The road lens <b>220</b> includes an inside made of optical glass or optical plastic. Alternatively, the inside of the road lens <b>220</b> may be a vacant space. Also, the outer wall of the road lens <b>220</b> is coated with a total reflection material. In addition, an opening <b>224</b> is formed in an input surface <b>222</b> so that the light generated by the lamp <b>210</b> can be incident into the inside of the road lens <b>220</b>. The remaining region <b>226</b> except for the opening <b>224</b> is coated with a reflection material. Like this, it is desirable that the region <b>26</b> is coated with a reflection material such that the light reflected by the color wheel <b>230</b> and inputted into the road lens <b>220</b> is reflected again and outputted onto the color wheel <b>230</b>. Accordingly, the road lens <b>220</b> receives the light generated by the lamp system <b>210</b> through the opening <b>224</b>, totally reflects it therein and outputs it to the color wheel <b>230</b> through an output surface <b>228</b>.

[0023] Although the light generated by the lamp system <b>210</b> has a low uniformity in brightness, it is outputted uniformly through the output surface <b>228</b> by the total reflection in the inside of the road lens <b>220</b>. Here, the brightness uniformity is changed depending on the length of the road lens <b>220</b> and a kind of the medium.

[0024] The light outputted from the road lens <b>220</b> passes the color wheel <b>230</b> or is reflected by the color wheel <b>230</b>. At this time, the light reflected by the color wheel <b>230</b> is again incident into the road lens <b>220</b>, is totally reflected inside the road lens <b>220</b> and is again outputted to the color wheel <b>230</b>. Here, the light outputted to the color wheel <b>230</b> has a different light path than the light outputted from the road lens <b>220</b>. This is because the angle of the light reflected by the color wheel <b>230</b> and the position of the light reflected totally in the road lens <b>220</b> are different from those of the first outputted light. For example, if the first outputted light is inputted to the color wheel <b>230</b> via the center of the output surface <b>228</b> of the road lens <b>220</b>, the light reflected by the color wheel <b>230</b> can be again inputted to the position other than the center of the output surface <b>228</b> of the road lens <b>220</b> according to the reflection angle. Also, since the re-inputted lights are reflected totally at different locations inside the road lens <b>220</b>, the final position of the light outputted to the output surface <b>228</b> of the road lens <b>220</b> becomes different from the position of the light first outputted to the color wheel <b>230</b>. Similarly, since the first light outputted to the color wheel <b>230</b> is different from the final light outputted to the color wheel <b>230</b>, each color light can be transmitted.

[0025] The color wheel <b>230</b> is arranged to face the output surface <b>228</b> of the road lens <b>220</b> at the same area. The R, G and B transmission filters are formed in a spiral configuration. By forming the transmission filters in a spiral configuration, R, G and B color lights can be outputted through the transmission filters uniformly.

[0026] Thus, when the color wheel <b>230</b> is comprised of spiral filters, the color lights outputted through the color wheel <b>230</b> have curved boundary surfaces <b>234</b> and <b>236</b>.

[0027] As shown in FIG. 5, when the color wheel <b>230</b> is rotated by a motor <b>232</b>, R, G and B transmission filters move sequentially to pass the corresponding color lights selectively. After that, if the passed color lights are incident into the image display device <b>250</b> through the converging lens <b>240</b>, color lights having the curved boundary surfaces <b>234</b> and <b>236</b> appear.

[0028] To this end, there is required an algorithm for converting the color lights having the curved boundary surfaces <b>234</b> and <b>236</b> to a linear type of color lights. However, the algorithm for converting the color lights having the curved boundary surfaces <b>234</b> and <b>236</b> to a linear type of color lights is very complex, which is problematic.

[0029] In the meanwhile, to convert the color lights having the curved boundary surfaces <b>234</b> and <b>236</b> to a linear type of color lights, it is desirable that the color wheel is made as great as possible. However, the use of the great color wheel causes a problem that the volume of the color wheel increases. Of course, even if the color wheel is made great, the boundary surfaces <b>234</b> and <b>236</b> are not perfectly converted to a linear arrangement.

[0030] Also, as shown in FIG. 6, the flat color wheel <b>230</b> of the conventional projector faces the output surface <b>228</b> of the road lens <b>220</b>. To this end, in case the lights outputted through edges of the road lens <b>220</b> are reflected by the color wheel <b>230</b>, the reflected lights are not re-inputted to the road lens but are lost outside the road lens <b>220</b>. As a result, the loss of the light outputted through edges of the road lens reduces the whole light brightness.

SUMMARY OF THE INVENTION

[0031] Accordingly, the present invention is directed to an optical system and display device using the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[0032] An object of the present invention is to provide a display device in which a cylindrical color drum is used to reduce light loss occurring between a road lens and the color drum as great as possible and thus enhance light efficiency.

[0033] Another object of the present invention is to provide a display device in which a rectangular transmission filter is provided on a cylindrical color drum to output a linear boundary surface and thus simplify the signal processing of the display device.

[0034] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0035] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an optical system. The optical system includes: a road lens for totally reflecting light inputted from an outside, changing a path of the light and outputting the light; a cylindrical color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light so that the light outputted from the road lens is transmitted selectively; and a converging lens for converging the light transmitted through the color drum.

[0036] According to the optical system, the road lens includes: an input surface having an opening for transmitting the light inputted form the outside and a reflection region coated with a reflection material; side portions for totally reflecting the light inputted though the input surface; and an output surface for outputting the total reflected light from one of the side portions. Here, the road lens further includes a reflecting surface slanted by a predetermined angle from the output surface to change the path of the light inputted though the input surface. Also, the output surface includes an opening sized to at least include the plurality of cell filters of the color drum.

[0037] The plurality of cell filters of the color drum have surfaces arranged to face the output surface in the form of a curved surface. Alternatively, the plurality of cell filters are arranged in a linear type.

[0038] According to the optical system, the road lens includes: a side portion; an input surface formed at a predetermined region of the side portion, the input surface having an opening through which the light inputted from the outside is transmitted and a reflection region, the side portion totally reflecting the light inputted though the input surface; and an output surface for outputting the total reflected light. The road lens further includes a reflecting surface slanted by a predetermined angle from the output surface to change the path of the light inputted through the input surface.

[0039] In another aspect of the present invention, there is provided a display device of magnifying and projecting a small-sized image to display a large-sized image, the device includes: a lamp system for generating light and converging the light; an optical system including a road lens for uniformly outputting the light converged by the lamp system, a color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light outputted from the road lens, and a converging lens for converging the light transmitted through the color drum; an image display device for expressing the light converged by the optical system in colors according to an applied electric signal; and a projecting system for magnifying and projecting the colors expressed by the image display device.

[0040] According to the display device, the road lens includes: an input surface to which the light generated by the lamp system is inputted; a side portion for totally reflecting the light inputted through the input surface; an output surface for projecting the light reflected totally by the side portion to the color drum; and a reflecting surface slanted by a predetermined angle from the output surface, for changing a path of the light inputted from the lamp system.

[0041] Also, the road lens includes: an input surface to which the light generated by the lamp system is inputted; a reflecting surface slanted by a predetermined angle from the input surface, for changing the path of the light inputted from the lamp system; a side portion for totally reflecting the light the path of which is changed by the reflecting surface, the input surface being formed on a predetermined region of the side portion; and an output surface for outputting the light reflected totally by the side portion to the color drum.

[0042] In another aspect of the present invention, there is provided a display device of magnifying and projecting a small-sized image to display a large-sized image. The device includes: a lamp system for generating light and converging the light; a road lens for uniformly and totally reflecting the light converged by the lamp system; a color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light outputted from the road lens; a converging lens for converging the light transmitted through the color drum; an image display device for expressing the light converged from the optical system in colors according to an electric signal; and a projecting system for magnifying and projecting the colors expressed by the image display device.

[0043] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

[0045]FIG. 1 illustrates a conventional projector in which color filters are attached to an image display device;

[0046]FIG. 2 illustrates a conventional projector in which a micro lens is attached to an image display device;

[0047]FIG. 3 illustrates a conventional projector using a color wheel;

[0048]FIG. 4 illustrates a conventional projector which includes a road lens;

[0049]FIG. 5 illustrates a scroll according to a rotation of the color wheel of the projector shown in FIG. 4;

[0050]FIG. 6 illustrates that light is transmitted through and is reflected by the color wheel of the projector shown in FIG. 4;

[0051]FIG. 7 is a schematic view of a projector using a color drum according to a preferred embodiment of the present invention;

[0052]FIG. 8 is a schematic view of the color drum of the projector shown in FIG. 7;

[0053]FIG. 9 illustrates that light travels between the road lens and the color drum in the projector shown in FIG. 7;

[0054]FIG. 10 illustrates that light is transmitted through and reflected by the color drum of the projector shown in FIG. 7;

[0055]FIG. 11 illustrates a scroll according to a rotation of the color drum of the projector shown in FIG. 7;

[0056]FIG. 12 is a schematic view of a projector using a color drum according to another preferred embodiment of the present invention; and

[0057]FIG. 13 is a schematic view of a projector using a color drum according to another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0058] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0059]FIG. 7 is a schematic view of a projector that includes a color drum according to a preferred embodiment of the present invention.

[0060] Referring to FIG. 7, the projector includes a lamp system <b>410</b> for generating light and converging the generated light around a focus, a road lens <b>420</b> for totally reflecting the light inputted from the lamp system <b>410</b>, changing a path of the light and outputting the lights, a scroll unit <b>430</b> having cell filters arranged orderly in a cylindrical construction and facing the path of the light so as to transmit the light outputted from the road lens <b>420</b> selectively, a converging lens <b>440</b> for converging the light transmitted through the scroll unit <b>430</b>, an image display device <b>450</b> for expressing colors by using the light of the converging lens <b>440</b> according to an applied electric signal, and a projecting system <b>460</b> for magnifying and projecting the colors expressed by the image display device <b>450</b>. Here, the scroll unit <b>430</b> is preferably provided with a color drum <b>436</b> that is rotatable by a motor <b>432</b>.

[0061] The lamp system <b>410</b> includes a light source <b>412</b> for generating the light and an elliptic reflecting mirror <b>414</b> for controlling the generated light to be inputted to the road lens <b>420</b>. In other words, the elliptic reflecting mirror <b>414</b> has a geometrical structure such that all the light generated by and inputted from the light source <b>412</b> is reflected and focused in the vicinity of an input surface of the road lens <b>420</b>.

[0062] The road lens <b>420</b> is shaped in a rectangular, and includes an input surface <b>421</b>, a side portion <b>424</b>, a reflecting surface <b>428</b> and an output surface <b>426</b>. The input surface <b>421</b>, as shown in FIG. 9, consists of an opening <b>422</b> through which light generated from the lamp system <b>410</b> is passed, and a reflection region <b>423</b> for reflecting the light, which is reflected by the scroll unit <b>430</b> and returns to the inside of the road lens <b>420</b>, and outputting the reflected light to the scroll unit <b>430</b>. The reflection region <b>423</b> is a region other than the opening <b>422</b> and is coated with a reflection material.

[0063] The side portion <b>424</b> includes the output surface <b>426</b> formed at a predetermined region thereof. The output surface <b>426</b> outputs the light inputted to the inside of the road lens <b>420</b> to the scroll unit <b>430</b>. Here, it is desirable that the output surface <b>426</b> includes an opening. Usually, the opening of the output surface <b>426</b> is greater than the opening <b>422</b> of the input surface <b>421</b>. This is because the opening <b>422</b> of the input surface <b>421</b> is required to pass only the light converged by the lamp system <b>410</b> but the opening <b>422</b> of the output surface <b>426</b> is required to output to the outside all the lights which is reflected by the reflecting surface <b>428</b> to have a wide reflection angle distribution. In other words, it is desirable that the opening of the output surface <b>426</b> is as big as a size including three cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>of the color drum <b>436</b> at least. Or, it is desirable that the opening of the output surface <b>426</b> is as big as a size including the number of the cell filters of the used colors R, G and B.

[0064] The road lens <b>420</b> further includes a reflecting surface <b>428</b> between the input surface <b>421</b> and the output surface <b>426</b> to change a light path. It is desired that the reflecting surface <b>428</b> is slanted from the output surface <b>426</b> by a predetermined angle. Accordingly, the light inputted through the input surface <b>421</b> is reflected by the reflecting surface <b>428</b> with a predetermined angle and outputted to the scroll unit <b>430</b> through the output surface <b>428</b>. Or the reflection surface <b>428</b> may be coated with total refection material or have a piece of total reflection mirror. The light inputted through the input surface <b>421</b> is reflected totally by the side portion <b>424</b> and outputted through the output surface <b>426</b> via the reflection surface <b>428</b>.

[0065] The road lens <b>420</b> is provided with the reflecting surface <b>428</b> for changing light path between the input surface <b>421</b> and the output surface <b>426</b>. The reflecting surface <b>428</b> is preferably inclined to have a predetermined angle with respect to the output surface <b>426</b>. Accordingly, the light that is inputted through the input surface <b>421</b> is reflected at a predetermined angle and is then outputted to the scroll unit <b>430</b> through the output surface <b>426</b>. Or, the reflecting surface <b>428</b> may be configured to be coated with a total reflection material and have an attached piece of a total reflection mirror. The light inputted through the input surface <b>421</b> may be totally reflected at the side portion and be outputted through the output surface <b>426</b> via the reflecting surface <b>428</b>.

[0066] In the meanwhile, some of the light outputted through the output surface <b>426</b> is transmitted by the scroll unit <b>430</b> and others of the light are reflected and inputted into the inside of the road lens <b>420</b> through the output surface <b>426</b>. At this time, the light inputted through the output surface <b>426</b> is reflected by the reflecting surface <b>428</b>, totally reflected by the side portion <b>424</b>, reflected at the reflecting area <b>423</b> of the input surface <b>421</b>, reflected by the reflecting surface <b>428</b> and outputted to the scroll unit <b>430</b>. Thus, the light reflected by the scroll unit <b>430</b> is totally reflected by the road lens <b>420</b> and is transmitted through the scroll unit <b>430</b>, which means that the reuse of the light becomes possible and thus the light efficiency is enhanced.

[0067] As shown in FIG. 8, the scroll unit <b>430</b> includes a motor <b>432</b> for generating a rotational force, a color drum <b>436</b> rotating by the rotational force of the motor <b>432</b>, and a coupler <b>434</b> which is an intermediate to connect the color drum <b>436</b> to the motor <b>432</b>. The color drum <b>436</b> is cylindrical to surround the side portion <b>424</b> of the road lens <b>420</b>. As shown in FIG. 9, the color drum <b>436</b> may have R, G and B cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>arranged in a cylindrical shape or in a combination of a plurality of color cell filters. It is desirable that the cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>are arranged in a linear shape. At this time, it is desirable that the surfaces of the R, G and B cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>face the output surface <b>426</b> of the road lens <b>420</b>.

[0068] Accordingly, the light outputted through the output surface <b>426</b> of the road lens <b>420</b> is inputted to one of the R, G and B cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c. </i>At this time, when the transmission condition is satisfied, the light is transmitted and inputted to the converging lens <b>440</b>. When the transmission condition is not satisfied, the light is reflected and returns to the inside of the road lens <b>420</b> through the output surface <b>426</b>. The returning light is reused by the road lens <b>420</b> and is outputted to the color drum <b>436</b>. For example, if the light outputted from the road lens <b>420</b> is inputted to the R cell filter <b>438</b><i>c, </i>the R color light is transmitted but the other color lights are not transmitted but reflected and inputted to the road lens <b>420</b>. Continuously, if the light that is reflected totally by the road- lens <b>420</b> and outputted again is inputted to the G cell filter <b>438</b><i>b, </i>the G color light is transmitted but the other color lights are reflected and inputted to the road lens <b>420</b> again. Through such a procedure, the corresponding color light can continue to be transmitted through the corresponding cell filter.

[0069] In the related art, the color wheel is formed to be flat as shown in FIG. 6. Therefore, if the light outputted to the color wheel is reflected, some of the light is not inputted to the road lens and lost to outside. However, if the light outputted to the color drum <b>436</b> does not satisfy the transmission condition and is reflected, the cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>of the color drum <b>436</b> form a curved surface with respect to the output surface <b>426</b> even though the light outputted from the road lens <b>420</b> as shown in FIG. 10 is reflected by the color drum <b>436</b>. So, the reflection angle of the color drum <b>436</b> becomes smaller and the light that is used to be lost to outside can be again inputted to the road lens <b>420</b>. Accordingly, the amount of the lost light is reduced compared with that of the related art and the light efficiency is enhanced to implement an image having a uniform brightness.

[0070]FIG. 10 illustrates a scroll according to the rotation of the color drum of the projector. As shown in FIG. 10, while the color drum <b>436</b> is rotated, the corresponding color lights are transmitted through the cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>of the color drum <b>436</b>. Here, since the cell filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>arranged on the color drum <b>436</b> are arranged in a linear shape as shown in FIG. 8, the boundary surfaces <b>437</b> and <b>438</b> between the color lights transmitted through the color filters <b>438</b><i>a, </i><b>438</b><i>b </i>and <b>438</b><i>c </i>are all in a linear shape as shown in FIG. 11. The use of these linear type color lights enables the image display device <b>450</b> to use the linear scroll illumination, so that the signal process of the image display device <b>450</b> can be simplified.

[0071]FIG. 12 is a schematic view of a projector that includes a color drum according to another preferred embodiment of the present invention.

[0072] Referring to FIG. 12, a projector according to another preferred embodiment of the present invention includes a reflecting surface <b>477</b> slanted by a certain angle from an input surface <b>471</b> of a road lens <b>470</b> and changes the path of the light inputted to the input surface <b>471</b>. By constructing the road lens <b>470</b> as above, the road lens <b>470</b> can be completely inserted into the color drum <b>436</b>, so that the size of the projector can be reduced.

[0073] Here, the input surface <b>471</b> of the road lens <b>470</b> is formed at a predetermined region of a side portion <b>473</b>. Like that shown in FIG. 7, an opening is formed at the center of the road lens <b>470</b>, and a region, i.e., reflection region other than the opening, is coated with a reflection material. An output surface <b>475</b> is formed on the light path formed between the reflecting surface <b>477</b> and the color drum <b>436</b>. The output surface <b>475</b> consists of the opening to output the light reflected by the reflecting surface <b>477</b>.

[0074]FIG. 13 is a schematic view of a projector that includes a color drum according to another preferred embodiment of the present invention. As shown in FIG. 13, the projector according to another preferred embodiment of the present invention is a modified fashion of the projector shown in FIG. 7, in which the image display device is changed from the transmission type to the reflection type. Accordingly, the light converged by the converging lens <b>440</b> is expressed in colors by an image display device <b>480</b> and is reflected. The reflected light is then magnified and projected onto the projecting system <b>460</b>. Since the lamp system <b>410</b>, the road lens <b>420</b> and the color drum <b>436</b> have the same structure of those shown in FIG. 7, their detailed description will be omitted.

[0075] Thus, the projector according the present invention can be applied to all of the reflection type image display device and the transmission type image display device.

[0076] As described above, according to the display device of the present invention, there is provided a color drum on which cell filters are arranged to face the output surface in a curved surface shape. In addition, the cell filters are arranged cylindrically to surround the road lens. The cell filters of the color drum are formed in a linear shape.

[0077] Thus, since the cell filters are arranged in a curved surface shape, the loss of the light reflected by the color drum to the outside is prevented to the maximum extent to improve the light efficiency. Accordingly, the light brightness is enhanced further.

[0078] In addition, the linear scroll is possible due to the existence of the cell filters that are linear-shaped, so that separate linear scroll illumination is not required and the signal process can be simplified.

[0079] Furthermore, the road lens can be installed in the cylindrical color drum to reduce the overall size of the device, which enables the device to meet the current trend of the thin characteristic.

[0080] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.