JPH07104713A - Overhead projector - Google Patents

Abstract

PURPOSE:To provide an overhead projector without copying an original on a transparent film and capable of clearly enlarging and projecting even the halftone original. CONSTITUTION:The contents of an original 1 are picked up by an imaging device 5, the signal Si of an A/D converter 6a in which an image signal is A/D-converted and a compensated threshold signal Sh2 are compared by means of a comparator 6b and binarized. The compensated threshold signal Sh2 is generated in a compensation pattern memory 6d based on a compensated pattern in accordance with the illuminated state of the original from a reference threshold value Sh1. The output of a halftone color compensating circuit 6 is converted into a liquid crystal driving signal in a signal processing circuit 7, outputted to a liquid crystal panel 10 and the contents of the original 1 are displayed on the liquid crystal panel 10. A light beam emitted from a lamp 8 is introduced to the liquid crystal panel 10 by means of a cold mirror 9. By reflecting the light beam passing through the liquid crystal panel 10 by means of a total reflection mirror 11 and projecting it by means of a projection lens 12, the original 1 is projected on a screen.

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 an opaque original as it is.

[0002]

2. Description of the Related Art Conventionally, there is an overhead projector (hereinafter referred to as OHP) which projects light onto a transparent film from below, for example, and projects it onto a screen or the like by a projection lens and a mirror. In such an OHP, an original is once copied onto a transparent film for OHP, and the original is enlarged and projected by irradiating the transparent film with light from a lamp. There is also a type called a reflection type, in which strong light is applied to a document and the reflected light is projected by a lens.

[0003]

Since the conventional OHP projects the original document as described above, there is a problem that the original document of plain paper must be copied onto a transparent film. Also, with a reflection type OHP, it is not necessary to make a copy on the film, but since it is projected by the reflected light from the original, it is difficult to see in the shade of an intermediate color original such as that written on straw half-paper, and it becomes difficult to see, and the amount of light that hits the original is reduced. Due to the unevenness, there is a problem that the clarity of the projected original differs within the original. SUMMARY OF THE INVENTION It is an object of the present invention to provide an overhead projector capable of enlarging and projecting a document of an intermediate color with high clarity without having to copy the document on a transparent film in order to solve the above problems.

[0004]

According to the present invention, there are provided an illumination for illuminating a document, an image sensor for reading the document, an A / D converter for A / D converting an image signal output from the image sensor, and a reference threshold value. A reference threshold value generator that generates a signal, a correction pattern storage device that stores a correction pattern according to the illumination state of a document and converts the reference threshold value signal into a correction threshold value signal based on this correction pattern, A / D A comparator for comparing the output signal of the converter with the correction threshold signal to binarize the output signal;
In the light source, an intermediate color correction circuit including a D / A converter for D / A converting the output of the comparator, a signal processing circuit for converting an output signal of the D / A converter of the intermediate color correction circuit into a liquid crystal drive signal, and a light source It has a certain lamp, a liquid crystal panel which is arranged so that the light from the lamp is incident and performs display based on a liquid crystal drive signal, and a projection lens which projects the light passing through the liquid crystal panel onto a screen.

[0005]

According to the present invention, a document is imaged by the image pickup device and converted into an image signal, which is A / D converted by the A / D converter in the intermediate color correction circuit and A / D by the comparator. The output signal of the converter is compared with the correction threshold signal to binarize the output signal. At this time, the correction threshold value signal is generated in the correction pattern storage unit from the reference threshold value signal output from the reference threshold value generator based on the correction pattern according to the illumination state of the document. Then, the output of the comparator is D / A converted by the D / A converter, and D
The output signal of the / A converter is converted into a liquid crystal drive signal by the signal processing circuit and output to the liquid crystal panel. Then, the light emitted from the lamp enters the liquid crystal panel, and the light passing through the liquid crystal panel is projected on the screen by the projection lens.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) shows an OHP showing one embodiment of the present invention.
FIG. 1B is a block diagram of the OHP intermediate color correction circuit. In FIG. 1A, 1 is a document, 2 is a document glass for setting the document 1, 3 is document illumination such as a fluorescent lamp for illuminating the document 1, and 4 is light reflected from the document 1 over the entire visible range. Total reflection mirror,
Reference numeral 5 is an image pickup element for converting the incident light from the total reflection mirror 4 into an image signal, and 6 is an intermediate color correction circuit for binarizing the image signal output from the image pickup element 5 in order to clearly project the original 1 of the intermediate color. , 7 are signal processing circuits for converting the output signals of the intermediate color correction circuit 6 into liquid crystal drive signals.

Further, 8 is a lamp which is a light source for projection, and 9 is a lamp.
Is a cold mirror that reflects visible light and transmits infrared light in the light emitted from the lamp 8, 10 is a liquid crystal panel, 1
Reference numeral 1 is a total reflection mirror that reflects the light that has passed through the liquid crystal panel 10, 12 is a projection lens for projecting the light from the total reflection mirror 11 onto a screen (not shown), and 13 is a casing.

In FIG. 1B, 6a is an A / D converter which outputs a signal Si obtained by A / D converting the image signal output from the image pickup device 5, and 6b is an output signal of the A / D converter 6a. A comparator for binarizing the output signal Si by comparing Si with the correction threshold signal Sh2, 6c is a reference threshold generator for generating a reference threshold signal Sh1 having a constant level value, and 6d is A correction pattern storage unit that stores a correction pattern corresponding to the illumination state of the original 1 and converts the reference threshold value signal Sh1 into a correction threshold value signal Sh2 based on this correction pattern, and 6e is the output signal So of the comparator 6b. It is a D / A converter that performs A / A conversion and outputs to the signal processing circuit 7.

Next, the operation of such an OHP will be described. First, the original 1 is set face down on the original glass 2 placed on the casing 13. The document surface of the set document 1 is illuminated by the document illumination 3. Then, the total reflection mirror 4 reflects the light from the document 1 and makes it enter the image pickup device 5.

The image pickup device 5 picks up the content of the original 1 and converts it into an image signal, which is output to the intermediate color correction circuit 6. Next, the intermediate color correction circuit 6 outputs the image signal output from the image pickup device 5 in order to clearly project the content of the original 1 of the intermediate color, for example, the original 1 of which the shade is unclear written on the straw half-paper. Is binarized as follows.

FIG. 2 is a diagram showing a document surface of a document 1 for explaining the operation of the intermediate color correction circuit 6, and FIG. 3 is a diagram showing signals of respective parts of the intermediate color correction circuit 6. 2 (a) is shown in FIG.
The original surface of the blank original 1 which is set face down in the OHP of (a) and is illuminated by the original illumination 3 is shown, and since the light from the original illumination 3 is not uniform, the original 1 is slightly bright and dark. There is a difference between. The shaded area on the original 1 is the dark area. In addition, FIG. 2B shows a manuscript 1 in which the letter “A” is written.
The case is shown as in FIG. 2 (a).

FIGS. 3A to 3D show signals of the intermediate color correction circuit 6 in one horizontal scanning section of the image pickup device 5. Since these are signals after A / D conversion by the A / D converter 6a, they are originally discrete signals,
Here, it is represented as a continuous signal.

The A / D converter 6a in the intermediate color correction circuit 6 converts the image signal output from the image pickup device 5 into, for example, a 256-tone digital signal Si. Here, the image sensor 5
If the horizontal scanning of is performed from left to right in FIG.
The signal Si output from the A / D converter 6a as a result of the image of the blank original document 1 in FIG. 2A has a level variation as shown in FIG. It occurs and does not reach a certain level as it should be.

Similarly, the signal Si when the original 1 in FIG. 2 (b) is imaged is as shown in FIG. 3 (b) in the horizontal scanning section at the position H in FIG. 2 (b). That is, in addition to the portion of the signal Si having a low signal level due to the letter “A”,
The same level fluctuation as in (a) will occur.

The comparator 6b compares such a signal Si with a correction threshold value signal Sh2, which will be described later, and binarizes it.
The binarized signal So is output. Normally, binarization converts an input signal into "0" or "1" at an appropriate threshold value of a constant level. For example, the signal Si of FIG. When the digitization is performed, the value becomes “0” even in the portion other than the character “A” due to the level variation as described above.

Therefore, in order to correct the above-mentioned problem in the binarization for making the original 1 clear, the reference threshold value generator 6c and the correction pattern memory 6d make the uneven illumination as follows. Corrected threshold signal Sh2 considering
To occur. First, the reference threshold generator 6c is
0 if the converter 6a performs 256-tone A / D conversion
Correction threshold value signal Sh2
The reference threshold signal Sh1 which is the source of the signal is generated.

Next, the correction pattern storage unit 6d is shown in FIG.
A correction pattern according to the illumination unevenness as shown in (a) is stored in advance, and the reference threshold value signal Sh1 output from the reference threshold value generator 6c is used as the correction threshold value signal Sh2 based on this correction pattern. And output to the comparator 6b.

Therefore, as shown in FIG. 3 (b), the correction threshold value signal Sh corresponding to the level variation of the illumination unevenness with respect to the signal Si is obtained.
2 is output, the signal Si and the correction threshold value signal Sh2 are compared by the comparator 6b, as shown in FIG.
As shown in FIG. 2, the correct output signal So according to the content of the original 1 in FIG. 2B can be obtained.

Therefore, a correction pattern corresponding to the uneven illumination of the original 1 is stored in advance in the correction pattern storage device 6d, and the value of the reference threshold value signal Sh1 output from the reference threshold value generator 6c is supplied from the outside, for example. If it is changed according to the content of the original 1 by the operation, the level of the correction threshold value signal Sh2 is set to the reference threshold value signal S2.
Since it changes vertically in parallel according to h1, it is possible to perform binarization according to the original 1 in consideration of uneven illumination.

Thus, the binarized signal So is output from the comparator 6b to the D / A converter 6e, and the D / A converter 6
It is D / A converted by e and output to the signal processing circuit 7. Then, the output signal of the intermediate color correction circuit 6 is converted into a liquid crystal drive signal by the signal processing circuit 7 and output to the liquid crystal panel 10. In this way, the content of the original 1 is displayed on the liquid crystal panel 10.

On the other hand, the light emitted from the lamp 8 which is a light source is guided to the liquid crystal panel 10 by the cold mirror 9. At this time, the cold mirror 9 transmits harmful infrared rays and reflects only visible light. Therefore, the total reflection mirror 11 reflects the light passing through the liquid crystal panel 10 and the projection lens 12 projects the light, whereby the original 1 is projected on a screen or the like not shown.

[0022]

According to the present invention, it is not necessary to copy an opaque plain paper original on a transparent film, and the enlarged projection can be performed with high clarity as it is, and binarization is performed in consideration of uneven illumination. As a result, it is possible to perform a clear enlarged projection without unevenness even on a document having an unclear intermediate color.

[Brief description of drawings]

FIG. 1 is a block diagram of an OHP showing an embodiment of the present invention and a block diagram of an intermediate color correction circuit of the OHP.

FIG. 2 is a diagram showing a document surface illuminated by a document illumination.

FIG. 3 is a diagram showing signals of respective parts of an intermediate color correction circuit.

[Explanation of symbols]

 1 Original 3 Original Illumination 4 Total Reflection Mirror 5 Image Sensor 6 Intermediate Color Correction Circuit 7 Signal Processing Circuit 8 Lamp 10 Liquid Crystal Panel 11 Total Reflection Mirror 12 Projection Lens 6a A / D Converter 6b Comparator 6c Reference Threshold Generator 6d Correction pattern memory 6e D / A converter

Claims (1)

[Claims] 1. An illumination for illuminating an original, an image sensor for reading the original, and an A / D converter for A / D converting an image signal output from the image sensor.
A D converter, a reference threshold value generator for generating a reference threshold value signal, and a correction pattern corresponding to the illumination state of the document are stored, and the reference threshold value signal is converted into a correction threshold value signal based on this correction pattern. Correction pattern storage device, the A / D
A comparator for comparing the output signal of the converter with the correction threshold signal to binarize the output signal, and the output of this comparator is D /
An intermediate color correction circuit composed of a D / A converter for A conversion, a signal processing circuit for converting an output signal of the D / A converter of the intermediate color correction circuit into a liquid crystal drive signal, a lamp as a light source, and a light from the lamp An overhead projector comprising: a liquid crystal panel, which is arranged so as to enter the liquid crystal display device and performs a display based on the liquid crystal drive signal; and a projection lens which projects light passing through the liquid crystal panel onto a screen.