JP3436500B2 - Overhead projector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overhead projector, and more particularly to an overhead projector capable of enlarging and projecting both an opaque original and a transparent original.

[0002]

2. Description of the Related Art Recently, an overhead projector (to be referred to as an OHP hereinafter) capable of enlarging and projecting an opaque original without using a conventional transparent sheet as a device for presentations used in conferences and lectures at universities. Has been proposed (for example, JP-A-7-10471).
3 gazette). In this system, a document is picked up by a TV camera, and the picked-up image is projected on a screen by a projection display device. This OHP illuminates the material surface of the original set on the original table with the illumination inside the OHP to perform imaging. The reason for adopting such a configuration is that an image can be captured without being affected by light from the outside.

[0003]

However, in the above OHP, since it is assumed that an opaque original is used, when an original created using a transparent OHP sheet is projected, the original characters are white. There are problems such as blurring and the inability to reproduce intermediate colors (intermediate gradation). Such a problem occurs because the illumination light that has passed through the transparent original is reflected by the white original cover, so that the amount of light entering the camera from the original becomes higher than in the case of an opaque original. The present invention has been made to solve the above problems, and an object of the present invention is to provide an OHP capable of enlarging and projecting not only an opaque original but also a transparent original with high clarity.

[0004]

An overhead projector of the present invention reads a document (1) placed face down on a transparent document table (4) above a projector body (2) from below the document table. It is provided with a camera (7) and a projection display device (12) for projecting an image captured by the camera onto a screen. An original cover (3) having a backlight (16) that covers the area of the original table and illuminates the upper surface of the original is provided so as to be openable and closable with respect to the original table. In addition, one configuration example of the overhead projector is a first example that performs conversion processing for gamma correction corresponding to an opaque document on input image data acquired by a camera.
Of the first look-up table (9a), the second look-up table (9b) that performs conversion processing for gamma correction corresponding to the transparent original on the input image data, and the first look-up table and the second look-up table. It has a changeover switch (10) for selecting whether or not. The changeover switch selects the second look-up table when a transparent document detection signal indicating that a transparent document is placed on the document table is input, and when the transparent document detection signal is not input, the first switch is selected. The look-up table is selected to perform gamma correction on the input image data. Further, the document cover has a pair of hinges (15a, 15b) for opening and closing operations at one end thereof, and each of the hinges is a constituent member of the jack (14a, 14b) provided around the document table of the projector body. ), And one of the posts serves as a power supply terminal to the backlight, and the other post serves as an output terminal of a transparent original detection signal.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an OHP showing an embodiment of the present invention. In FIG. 1, 1 is a document, 2 is a projector body, and 3 is a document cover.

[0006] The projector main body 2 reflects an original table 4 made of transparent glass for setting the original 1, an original illumination 5 such as a fluorescent lamp for illuminating the original 1, and light from the original 1 over the entire visible range. A total reflection mirror 6, a camera 7 that converts incident light from the total reflection mirror 6 into an analog image signal, an A / D converter 8 that converts the analog image signal output from the camera 7 into digital image data, A
Look-up tables (hereinafter referred to as LUTs) 9a and 9b for performing conversion processing for gamma correction on the image data output from the / D converter 8 and switching for selecting either output of the LUTs 9a and 9b. A switch 10, a D / A converter 11 for converting the image data output from the changeover switch 10 into an analog image signal, and a screen (not shown) for converting the image signal output from the D / A converter 11 into optical information. And the like, and a power source 13 for generating a power source voltage to be supplied to the document cover 3.
And the jacks 14a and 14b to be fitted with the post of the document cover 3 which will be described later.

FIG. 2 is an external view of the document cover 3. The original cover 3 having the purpose of pressing the original 1 and a light-shielding function when the original 1 is smaller than the original table 4 is placed on the original table 4 and hinges 15a and 15b which serve as an opening / closing mechanism of the original cover 3. A backlight unit 16 that illuminates the upper surface (back surface) of the original document 1, a dimming volume control 17 for adjusting the emission intensity of the backlight unit 16, and an original document 1 to be projected is made using an opaque sheet. The document cover power switch 18 is turned off in the case of and the document cover power switch 18 is turned on in the case of a document created using a transparent OHP sheet (hereinafter, referred to as a transparent document).

The hinges 15a and 15b are composed of hinge boxes 19a and 19b fixed to the original cover 3, and posts 20a and 20b rotatably attached to the hinge boxes 19a and 19b by pins (not shown).
As shown in FIG. 3A, the posts 20a and 20b are jacks 1 provided around the document table of the projector body 2.
4a, 14b can be detachably fitted.

The posts 20a and 20b are connected to the jack 14a,
14b to fit the original cover 3 into the projector main body 2
3 is attached to the original cover 3 as shown in FIG.
As shown in (c), the hinges 15a and 15b are supported so as to be openable and closable with the pins (not shown) as rotating shafts. Also, jacks 14a, 14b and hinges 15a, 15b
Serves as a mechanical opening / closing mechanism for the document cover 3 and serves as a terminal for electrically connecting the projector body 2 and the document cover 3.

That is, the power source 13 of the projector main body 2
The power source voltage for the backlight unit 16 is supplied from the document cover 3 to the document cover 3 via the jack 14a and the post 20a, and when the document 1 is a transparent document, the post 20 is used.
A transparent original detection signal is supplied to the control input terminal of the change-over switch 10 via the jack b and the jack 14b. The backlight unit 16 is illumination using an FL (Fluorescent Lamp) panel or an EL (Electro-Luminescence) panel.

Next, as such an operation of OHP, a case where an opaque original 1 is enlarged and projected will be described. O
The user of the HP places the document 1 on the document table 4 with the document face down and closes the document cover 3. At this time, the user turns off the side for designating an opaque original, that is, the original cover power switch 18.

The document surface (lower surface) of the manuscript 1 is a manuscript illumination 5
Illuminated by The total reflection mirror 6 reflects the light from the set original 1 and makes it enter the camera 7. The camera 7 converts incident light into an analog image signal, and the A / D converter 8 converts the analog image signal into digital image data.

Next, the LUTs 9a and 9b perform the following conversion processing for gamma correction on the image data output from the A / D converter 8. FIG. 4A shows the LUT 9
FIG. 4B is a diagram showing the conversion characteristic of a and FIG. 4B is a diagram showing the conversion characteristic of the LUT 9b. LUTs 9a and 9b are shown in FIG.
4A is a memory for performing data conversion as shown by the solid line in FIG. 4B, and outputs image data of the same number of bits according to input image data of multiple bits. Note that FIG.
The input / output data value of indicates that the larger the value, the higher the brightness. Further, in FIG. 4, as an example of the process, 8
I / O data of bits (0 to 255) is handled,
It goes without saying that other numbers of bits may be used.

The change-over switch 10 selects one of the outputs of the LUTs 9a and 9b according to the signal input from the jack 14b to the control input terminal. At this time, since the original cover power switch 18 is in the state of designating an opaque original, that is, in the off state, the transparent original detection signal is not output. As a result, the changeover switch 10 becomes
Select the output of 9a.

The LUT 9a performs conversion processing as shown by the characteristic of FIG. 4A for gamma correction corresponding to the opaque original 1. The conversion characteristics of the LUT 9a are such that the luminance on the low luminance side is emphasized and the luminance on the high luminance side is saturated with respect to the linear input / output characteristic shown by the broken line in FIG. 4 (a). Due to such characteristics, good gradation characteristics can be obtained when the opaque original 1 is projected.

The D / A converter 11 converts the image data output from the LUT 9a via the change-over switch 10 into an analog image signal and outputs the analog image signal to the projection display device 12. The projection display device 12 converts the input analog image signal into optical information and projects it on a screen (not shown). In this way, the content of the original 1 can be enlarged and projected.

Next, the case of enlarging and projecting a transparent original will be described. When enlarging and projecting a transparent original, the user of the OHP turns on the side that specifies the transparent original, that is, the original cover power switch 18. As a result, the power supply voltage from the power supply 13 is supplied to the backlight unit 16 via the jack 14a, the post 20a, and the document cover power switch 18, and the backlight unit 16 is turned on.

The power supply voltage that has passed through the document cover power supply switch 18 is supplied to the control input terminal of the changeover switch 10 via the post 20b and the jack 14b. The voltage input to the changeover switch 10 is the transparent original detection signal. When the transparent original detection signal is input, the changeover switch 10 selects the output of the LUT 9b.

The LUT 9b performs a conversion process as shown by the characteristic of FIG. 4B for gamma correction corresponding to the transparent original 1. The conversion characteristics of the LUT 9b are more linear input / output characteristics than the characteristics of the LUT 9a. this is,
This is because if the luminance is emphasized like in the LUT 9a, the intermediate gradation cannot be expressed well. Thus, when the transparent original 1 is projected, good gradation characteristics can be obtained. The subsequent operation is the same as the case of the opaque current 1.

As described above, in the present invention, the original cover 3
By providing the backlight unit 16 in and using the document cover 3 as a kind of Shark Sten, it is possible to deal with a transparent document. By adjusting the brightness of the backlight unit 16 using the dimming control volume 17, the gradation characteristics of the input image captured by the camera 7 can be adjusted more appropriately according to the actual transparent original.

[0021]

According to the present invention, by providing a backlight on the document cover, the brightness and gradation characteristics of the input image (transparent document) captured by the camera can be made good. As a result, when the transparent original is projected, the problem that the original characters are blurred or the intermediate color (intermediate gradation) cannot be reproduced does not occur.

Further, by providing the first and second look-up tables and the changeover switch to switch the look-up table for gamma correction between the case of an opaque original and the case of a transparent original, it is possible to obtain a better floor. It is possible to obtain tonality characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram of an OHP showing an embodiment of the present invention.

FIG. 2 is an external view of a document cover.

FIG. 3 is a diagram showing a method of attaching the document cover and an opening / closing operation of the document cover.

FIG. 4 is a diagram showing conversion characteristics of a lookup table.

[Explanation of symbols]

1 ... manuscript, 2 ... projector body, 3 ... manuscript cover, 4
... manuscript table, 5 ... manuscript illumination, 6 ... total reflection mirror, 7 ... camera, 8 ... A / D converter, 9a, 9b ... look-up table, 10 ... changeover switch, 11 ... D / A converter, 1
2 ... Projection display device, 13 ... Power supply, 14a, 1
4b ... Jack, 15a, 15b ... Hinge, 16 ... Backlight unit, 17 ... Dimming volume, 18 ... Original cover power switch, 19a, 19b ... Hinge box, 20a, 20b ... Post.

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Claims (3)

(57) [Claims] 1. A camera for reading an original placed on a transparent original table on the upper side of a projector main body from the lower side of the original table, and a projection display device for projecting an image captured by the camera on a screen. An overhead projector provided with the document projector, wherein a document cover provided with a backlight that covers a region of the document table and illuminates an upper surface of the document is provided so as to be openable and closable with respect to the document table. 2. The overhead projector according to claim 1, wherein the input image data obtained by the camera is subjected to a conversion process for gamma correction corresponding to an opaque document, and the input image is obtained. A second look-up table that performs conversion processing for gamma correction corresponding to a transparent original on data, and a changeover switch that selects either the first look-up table or the second look-up table are provided. , A second look-up table is selected when a transparent original detection signal indicating that a transparent original is placed on the original table is input, and a first look-up table is selected when the transparent original detection signal is not input. An overhead projector, wherein an up table is selected to perform gamma correction on the input image data. 3. The overhead projector according to claim 2, wherein the manuscript cover has a pair of hinges for the opening / closing operation at one end thereof, and each hinge serves as a constituent member thereof.
It has a post that is detachably fitted to a jack provided around the document table of the projector main body, one post serves as a power supply terminal to the backlight, and the other post receives the transparent document detection signal. An overhead projector characterized by being an output terminal.