JPH0365567B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a coordinate input device, and particularly to one that inputs position coordinates of an image or the like into a computer or the like using an imaging device.

[Conventional technology]

Tablets and mice are commonly used as coordinate input devices, but it is necessary to input coordinates only on a special flat surface, or to move a point pointing device with a signal cable attached, so devices such as tablets and mice are often used. It is not necessarily good in terms of operability. Further, the function is limited to inputting coordinates, and there is a problem in that it is difficult to input existing image data unless an image scanner or the like is prepared as an input device for an imaging device or the like. From this perspective,
Attempts have been made to realize a device that functions as both an image scanner and a coordinate input device using a TV camera. It is clear that imaging devices such as TV cameras have the function of image scanners, and if coordinates can be input by capturing an image of a point pointing device, it is possible to input coordinates without using a special flat table or point pointing device with a cable. , it is expected that input operations will be possible in an extremely natural state, and operability will be significantly improved.

Figure 6 shows, for example, the journal J67-D of the Institute of Electronics and Communication Engineers,
6 is a schematic configuration diagram showing the configuration of a coordinate input device using a TV camera published in No. 6, 1984. In the figure, reference numeral 11 indicates the subject, for example, a read manuscript (if the purpose is only to input coordinates, there is no need to capture the contents written on the manuscript; a blank sheet may be used; more generally, it is not a document or drawing, etc.). 12 is a writing pen as a point indicating device; 5 is a writing pen as a point indicating device;
0 is a TV camera that simultaneously images the original to be read 11 and the point indicator 12, 7 is an image memory that stores the output image signal of the TV camera 50, and 8 is a display device such as a CRT that displays the stored contents of the image memory 7 as an image. , 9 is an image processing device that processes the image data stored in the image memory 7 to detect the image of the pointing tool 12, and 6 is a controller that controls the image processing device 9.

The TV camera 50 images the entire document 11 to be read and the writing pen 12 at a rate of 30 frames per second, and the output image signal is stored in the image memory 7. The stored contents of the image memory 7 are displayed on the display device 8 and processed by the image processing device 9. The image processing device 9 is controlled by the controller 6, and when operating as an image scanner, the image processing device 9 is controlled by the image memory 7.
When the contents of the writing pen 12 are transferred as they are to a file memory (not shown) and operated as a coordinate input device, so-called image processing is performed to detect the image of the writing pen 12 from the image signal. This image processing includes, for example, threshold processing to separate the content written on the read document 11 and the image of the writing pen 12, spatial filtering such as low-frequency three waves, and a mask pattern selected based on the shape of the writing pen 12 and lighting conditions. The image processing device 9 is a dedicated device for performing these processes at high speed. Then, the image of the writing pen 12 is detected, and an address on the image memory 7 where an image signal corresponding to a specific portion such as the tip of the writing pen 12 is stored is output to the controller 6. The controller 6 obtains the coordinates of the point indicated by the writing pen 12 by converting this address into coordinates on the read document 11.
The speed of coordinate input through the above image processing (that is, the number of times coordinate values of a point are obtained per second) is determined by the imaging speed of the TV camera (30 frames per second) if the operation speed of the image processing device 9 is sufficiently large. If not, it will be determined by the image processing speed. If the image of the writing pen 12 can be detected only 15 times per second by image processing, the co-controller 6 controls the image signal in the image memory 7 to be updated only once every two frames.

[Problem that the invention seeks to solve]

Conventional coordinate input devices using TV cameras as explained above can only input coordinates at a maximum of 30 points per second because the TV camera's imaging speed of 80 frames per second is slow, and the input speed is slower than that of ordinary tablets. There is a problem in that it is difficult to use because it is too small and the movement of the point pointing device is restricted. Also, the number of scanning lines in one frame of a TV camera is about 500 lines, and if the length of the original document 11 to be read is 25 cm, there are 2 lines per frame.
The fact that coordinates can only be input with a small resolution of mm is also a problem that greatly limits practical applications.

This invention was made to solve these problems, and aims to provide a coordinate input device that uses an imaging device and has high coordinate input speed and resolution while maintaining good operability. purpose.

[Means for solving problems]

The coordinate input device according to the present invention includes a one-dimensional image sensor, a rotating scanning mirror that sequentially sends images of a subject and a pointing device on the subject to the one-dimensional image capturing element, and detects a rotation angle of the rotating scanning mirror. detector,
a controller that specifies the rotation angle and narrows down the scanning range to a specific area including the point indicator; an image memory that stores the output image signal of the one-dimensional image sensor at an address corresponding to the rotation angle; The image processing apparatus includes an image processing device that processes and detects the positional coordinates of the pointing tool, and the position of the pointing tool on the subject is determined based on this detection signal.

[Effect]

In this invention, since scanning is performed only in a specific area around the point pointing tool, the coordinate input speed is increased. Furthermore, since this specific area is scanned at high resolution, the resolution of coordinate input also becomes high.

〔Example〕

FIG. 1 is a schematic configuration diagram showing a coordinate input device according to an embodiment of the present invention. In the figure, 1 is a lens, 2 is an original 11 to be read by rotation, and a point indicator 1.
A rotary scanning mirror or galvanometer mirror 3 that sequentially sends images of 2 to a one-dimensional image sensor is a drive device that drives the rotary scan mirror, 4 is a one-dimensional image sensor, 5 is a detector that detects the rotation angle of the rotary scan mirror, and 6 7 is a controller such as a microprocessor that supplies a signal specifying the rotation angle that the rotating scanning mirror should take to the driving device 3; 7 is an image memory that stores the output image signal of the one-dimensional image sensor 4; 8 is the storage content of the image memory 9 is an image processing device that processes the image signal stored in the image memory to detect the position coordinates of the point pointing tool; This is a sub-sampling circuit that reduces the number of pixels.

In the coordinate input device configured as described above, a two-dimensional image of the original to be read 11 and the point indicator, that is, the writing pen 12, created by the lens 1 is reflected by the rotating scanning mirror 2 and captured by the one-dimensional image sensor 4. image on top. The rotating scanning mirror 2 is tilted to a specified rotation angle by a digital code or analog voltage signal that specifies the rotation angle of the rotating scanning mirror, which is generated from the controller 6 to the drive device 3, so that any part of the two-dimensional image can be tilted to a specified rotation angle. can be imaged on the one-dimensional image sensor 4, and this can also be used for sub-scanning to perform line-sequential scanning like a TV camera. The detector 5 is a mechanical or optical rotary encoder,
The current rotation angle of the rotating scanning mirror 2 is detected and a signal thereof is output, and the difference between the rotation angle specified by the controller 6 and the current rotation angle is calculated so that it can be used for rotation angle control. The primary element 4 driven by an image sensor driving circuit (not shown) performs an imaging operation in synchronization with sub-scanning, and the output image signal has only the necessary portions selected by the subsampling circuit 10. It is later stored in the image memory 7,
The stored contents are displayed on the display device 8 as an image.
At the same time, the image signal stored in the image memory 7 is processed by the image processing device 9 in the same manner as in the conventional device, and by detecting the image of the writing pen 12, writing is performed from the storage address of the specific portion. The coordinates of the point indicated by the pen 12 in the specific area are detected. The controller 6 determines the position of the writing pen 12 on the read document 11 from this detection signal, and inputs the position coordinates to a computer or the like. In addition,
The time when coordinates are input and the time when coordinates are not input are distinguished by a switch (not shown) attached to a writing pen or the like. The imaging scan in this example is conventional
Unlike a TV camera, the scanning target range and scanning resolution of the original document 11 to be read can be varied. In this embodiment, after the controller 6 sets the rotation angle of the rotary scanning mirror 2 at the boundary of the scanning target range in the document 11 to be read, the controller 6 sets the rotation angle to be changed stepwise by minute amounts. It generates a rotation angle designation signal at a high speed and performs line sequential scanning.

At this time, the size of the scanning target range in the sub-scanning direction corresponds to the rotation angle range of the rotary scanning mirror 2, and the scanning resolution corresponds to the minute step size of the rotation angle.

FIG. 2 is an explanatory diagram illustrating the imaging operation of the coordinate input device according to an embodiment of the present invention, and FIG.
is an example in which the scan target range is variable, and shows that the entire read document 11 may be the scan target range, or a part of the specific area 21 can be the scan target range. Further, FIGS. 2b and 2c are examples of variable scanning resolution, and FIG. 2b shows an example in which the scanning target range is scanned over the entire document 10 to be scanned at a relatively sparse scanning line density. Second
FIG. c shows a case where the scanning target range is narrowed down to a specific area 21 and scanning is performed with a relatively dense scanning line density.
In Fig. 2b, the minute step size of the rotation angle is increased to achieve high-speed scanning despite the large scanning target range, and in Fig. 2c, the minute step size of the rotation angle is decreased to achieve a small scanning target range. Scan at high resolution. FIG. 2d shows that the latter high-resolution scan of a small area causes the specific area 21 to be stored in the image memory 7 in an enlarged manner compared to the former wide-area high-speed scan. Further, FIGS. 2e and 2f are diagrams showing examples of image signal storage states in the image memory 7. The storage address of the image memory 7 is determined by the number of scanning lines to be searched, which is determined from the rotational angle range of the rotating scanning mirror 2 and the minute step size of the rotational angle, and the amount of image signals included in each scanning line, that is, the number of pixels per scanning line. are associated with each scanning line. Figure 2e shows an example of the storage state when the entire reading manuscript 11 is scanned with a large step size, and one line is 512 pixels.
Remember the line. The size of the original to be read 11 is
If it is 25cm x 25cm, this is about 2 in both length and width.
This corresponds to scanning with a resolution of pixels/mm, that is, a resolution comparable to that of a TV camera. In order to store the image signal of this resolution, the subsampling circuit 10
Now, a process of thinning out the output image signal of the one-dimensional image sensor 4 is performed. The reason for this is that since the one-dimensional image sensor 4 itself has a fixed number of picture elements, the output image signal is appropriately subsampled to obtain image signals with approximately the same resolution in the vertical and horizontal directions. For example, if the number of picture elements of the one-dimensional image sensor 4 is 2048, in order to obtain an image signal of 512 pixels in one line, one
A pixel is selected and stored in the image memory 7. On the other hand, the second
FIG. f shows an example of the storage state when the specific area 21 is scanned with small rotational angle steps. The ratio of the specific area 21 to the entire read document 11 is 1/2 horizontally,
Assuming that the height is 1/4, if this is the scanning target range and the resolution is approximately 5 pixels/mm, which is 2.5 times the above, an image signal of 640 horizontal pixels x 320 vertical lines will be stored in the image memory 7 as shown in Figure 2 f. be remembered. Note that in the figure, the shaded area is the blank area of the memory. At this time, in the main scanning direction (horizontal direction), the one-dimensional image sensor 4 captures an image of the entire width of 25 cm of the document 11 to be read, and the sampling circuit 10
640 pixels are obtained by subsampling so as to select 5 pixels from 8 pixels of the output image signal, and truncating 1/2 pixels outside the range of the specific area 21. Alternatively, by adjusting the focus of the lens 1, etc., a width of 40 cm including the entire document 11 to be read is captured by the one-dimensional image sensor 4.
The sub-sampling circuit 10 selects 640 pixels from the output image signal of the one-dimensional image sensor 4 by discarding pixels other than those within the specific area 21 and stores them in the image memory 7.
In other words, if the entire read document 11 is imaged in the specific area 21 with a sufficient main scanning resolution, it can be converted to the required resolution by the subsampling circuit 10. The sub-sampling operation corresponding to the size of the scanning target range and the scanning resolution as described above is performed by the controller 6 on the range (width) that can be imaged by the one-dimensional image sensor 4 and on the specific area 21.
This is usually done by a well-known method by giving the subsampling circuit 10 a signal that converts the position and size of the pixel array on the one-dimensional image sensor 4 to the required subsampling ratio. .

Furthermore, what should be added to the description of the imaging operation in FIG. 2 is the high speed of scanning using the rotating scanning mirror 2, especially the high speed when changing the scanning target range. The rotating scanning mirror 2 is lightweight and can reach the rotational angle specified by the controller 6 by the drive device 3 at high speed and precisely by being equipped with the detector 5, so that it can access any scanning target range. It takes only a short time, and it is also possible to perform minute steps in the rotation angle for line-sequential scanning at high speed, making it easy to achieve a scanning speed faster than that of a TV camera (512 lines x 30 frames per second). Rather, the upper limit of the scanning speed is determined by the operating speed of the one-dimensional image sensor 4 and the image processing device 9. Furthermore, it should be noted that even when scanning at high resolution, if the range to be scanned is appropriately limited, it is possible to scan the entire document 11 to be read at a higher speed than scanning at a resolution comparable to that of a TV camera. In the example shown in FIG. 2, if the operating speed of the one-dimensional image sensor 4 is the same, scanning the entire document 11 requires 512 lines of sub-scanning, while scanning the specific area 21 requires 320 lines of sub-scanning. Since scanning is sufficient, if the image processing device 9 is capable of real-time processing, a frame rate of 1.6 times, that is, a coordinate input speed can be realized, and the resolution is also 2.5 times higher.

From the above explanation, it has been made clear that the coordinate input device of the above embodiment can perform high-speed scanning of the original document 11 by making the scanning range and scanning resolution variable. Due to this property, it goes without saying that by using a TV camera as an image scanner in the same way as a conventional coordinate input device using a TV camera, superior performance can be obtained compared to one using a TV camera. In this way, more obvious advantages can be realized as a coordinate input device.

FIG. 8 is an explanatory diagram of the operation of a coordinate input device performed by an embodiment of the present invention having the configuration shown in FIG. Here, for simplicity, writing pen 12
First, a case in which drawing is not performed on the read original 11 will be explained. In that case, the position of the tip of the writing pen 12 can be determined by a method such as pattern matching by processing the image signal in the image memory 7 obtained by the scanning and imaging described above in the image processing device 9. The point coordinates are entered once in each frame. In FIG. 8a, the original to be read 1
In the process of moving the writing pen 12 relative to the
A specific area 31 is set that is about 4/1 the size of the original 11 both vertically and horizontally, and the coordinates of point 32 are input in the previous frame, and the coordinates of point 33 are input in the frame before that. It is assumed that At this time, the controller 6 calculates the moving direction of the writing pen 12 from the point 33 to the point 32, and sets the scanning target range in the next frame in that direction.
That is, the position of the specific area 31 is determined so as to sufficiently include the coordinates predicted to be detected in the next frame if the writing pen 12 continues to move, and is set as the scanning target range. The simplest position prediction method is to set the specific area 31 so as to sufficiently include a point symmetrical position with respect to the point 33 with respect to the point 32. The size of the specific area and the predicted relative position to the next position of the writing pen 12 should be determined based on the moving direction of the writing pen 12 and the magnitude of change in the moving speed. Here, it is assumed that a specific area 31 having a size of 1/4 of the length and width of the read document is simply set centered on a point 32 at the position of the writing pen in the immediately previous frame. When the coordinates of the point 34 are input by scanning the specific area 31 set in this way and image processing,
As shown in FIG. 3b, the scan target range for the next frame is set to a specific area 3 centered on the point 34.
5, and the point 36, which is the next position of the writing pen 12, is detected. In this way, the position of the specific area to be scanned next is determined according to the position of the writing pen 12 obtained by scanning the specific area once and performing image processing, so that the specific area tracks the writing pen 12. Coordinates are input in this way. As can be easily inferred from the explanation of FIG. 2, if the size of the specific area and the scanning resolution within it are appropriate, it is possible to input coordinates faster and with higher resolution than by repeatedly scanning the entire document 11 to be read. becomes. In this case, the rotating scanning mirror 2 changes the rotation angle range for scanning one frame after another in accordance with the rotation angle designation signal output from the controller 6, so that the same rotation angle becomes a minute step size. The sub-sampling circuit 10 also truncates pixels outside the area and performs sub-sampling in accordance with a signal output from the controller 6 indicating the range of the specific area and the sub-sampling ratio. Processing within the image processing device 9 is similar to that of conventional devices.

FIG. 4 is a flow chart showing an outline of the operation of the controller 6 according to an embodiment of the present invention as described above.

The controller 6 sets the rotation angle range and rotation angle step size to be taken by the rotary scanning mirror 2 in steps 61 and 62 in accordance with the scan target range of the original document 11 to be read. For example, when scanning the entire document 10 at high speed or when scanning a small area with high resolution, different starting angles (corresponding to the starting edge of the scanning target range) and ending angles (corresponding to the ending edge of the scanning target range) are used. )・Set the step size.
Further, in step 63, a signal indicating the ratio of subsamples and the effective range of the signal to be stored in the image memory 7 is output to the subsampling circuit 10, and further in step 64, the image signal to be stored in the image memory 7 is outputted. A signal indicating the update frequency or timing of the update is output.

After the above settings have been made, first, in step 65, a starting angle is set as the target value of the rotation angle that the rotating scanning mirror 2 should take, and in step 66, a signal specifying the target angle is given to the drive device 3. As a result, the rotating scanning mirror 2 rotates to take the target rotation angle, so in step 67 the output of the detector 5 is input to know the current rotation angle, and in step 68 it is confirmed that this matches the target angle. The same rotation angle designation signal is output until If the current angle matches the target angle, it is checked in step 69 whether it has reached the final angle. If the terminal angle has not been reached, step 7
At 0, the rotation step size is added to the current angle, this is set as the next target angle, and the process returns to step 66. By repeating steps 66 to 70, the range to be scanned is sequentially scanned from the beginning to the end at a predetermined step size.

If it is determined in step 69 that the current angle has reached the terminal angle, in step 71 the controller 6 receives the detected position of the image of the point indicator 12 (address on the image memory) from the image processing device 9, and Using information such as range and step size, the position on the read document, that is, the coordinates of the designated point, is calculated from the address on the image memory. This means that one coordinate input has been obtained. If the coordinate input state continues at step 72, the process advances to scanning for the next coordinate input, and if the coordinate input state is not present, the coordinate input ends. In order to input the next coordinates, in step 73, the coordinates of the point pointing tool 12 detected in the image captured by the previous scan (the previous frame) and the image captured by the current scan (the current frame) are entered. The direction of movement of the pointing tool 12 is calculated from the position, and based on this, the next scanning target range is determined in step 74, and the process returns to step 61 to start the next scanning.

As can be seen from the above explanation, the portion surrounded by the broken line in FIG.
8) corresponds to the operation of accessing the scanning position using the rotating scanning mirror 2, and the part surrounded by the dashed line (from step 61 to step 70) corresponds to the operation of line sequential scanning using the rotating scanning mirror 2. do. It is also possible to perform a random access operation using the access operation, or to perform trace scanning using line sequential scanning.

Note that in the above description, the rotation step size is not necessarily constant even during one scan. This is because the step size of the rotation angle of the rotary scanning mirror 2 may need to be changed minutely in accordance with the absolute value of the rotation angle in order to perform scanning on the original document 11 with a constant step size. . In such a case, the controller 6 stores changes in the step size of the rotation angle as a table, or calculates the step size from the absolute value of the rotation angle, and in step 70 stores the stored value or calculated value. Then, the next target angle is set using the following method.

Further, FIG. 5 is an explanatory diagram of a coordinate input operation in a coordinate input device according to an embodiment of the present invention, and unlike the case in FIG. do. In this case as well, the method for setting the position of the specific area is the same as that shown in FIG. A part of the process is illustrated. In the figure, the symbols attached to points and specific areas are the same as in Figure 8, but the image of the writing pen 12 (the diagonal line) and the drawing content (the solid line in the trajectory of the tip of the writing pen) are captured. and
In the specific area 31, the drawing content up to point 34 and the image 41 of the writing pen (the image signal of this frame is A) are obtained, and in the specific area 5, the drawing content up to point 36 and the writing pen image 42 (this frame , the image signal of which is denoted by B) is obtained. From image signal A and image signal B, a circuit performs a logical operation to obtain ・B (logical product of the inverted image of A and B. Here, A and B are assumed to be signals of binary logical values). If executed in a consistent manner, the drawing content up to the previous frame and the image of the writing pen 12 will be canceled out, and the drawing content from the newly drawn line 34 to point 36 and the new drawing content in the new frame will be canceled as shown in FIG. 5b. Only the writing pen image 42 remains, and the thin line (from point 34 to point 3), which is the new drawing content, remains.
6) and the image 42 of the writing pen can be easily separated by spatial filtering that eliminates thin lines, so the coordinates of the point 36 indicated by the tip of the writing pen are determined by the specific area 35 by image processing similar to conventional methods. The detected frame will be detected and input.

In the example shown in FIG. 5, it is necessary to know the corresponding parts of the image signals for the two frames in order to perform a logical operation between the two frames. Therefore, it is easy to correlate and calculate the image signals of successive frames on the image memory 7.
In the description of the embodiments so far, the case where the point pointing tool is a writing pen and its shape is detected by the image processing device 9 has been taken as an example, but the point pointing tool 12 is separated from the image signal by the image processing device. It may be any type of property as long as it can be identified. For example, using a thin cross-shaped object, an image processing device may be used to detect the intersection of the crosses.
A light-emitting element such as an LED is attached to the pen tip and an image processing device is used to detect a high brightness peak in the image signal, or a one-dimensional image sensor 4 that can input colors (for example, a one-dimensional image sensor with a color filter) ), it is natural that it is possible to detect the point pointing device and input coordinates by using a pen-shaped point pointing device of a different color from the original to be read and identifying the color with an image processing device. be.

In addition, in the explanation of the above embodiment, the setting of the size and position of the specific area to be moved was explained using a specific example so as to track a point pointing tool, but these are not limited to the exemplified size and setting method. Needless to say, it can be selected appropriately depending on how the point pointing tool is moved. Further, in the above embodiment, the subsampling circuit 10 is used to reduce the amount of image signals stored in the image memory 7, but the image memory itself has a sufficiently large storage capacity.
In addition, if necessary sub-sampling processing and high-speed processing are executed in the display and image processing stages, the sub-sampling circuit 10 between the one-dimensional image sensor 4 and the image memory 7 to reduce the number of pixels is unnecessary. Of course, it will be. Further, the coordinate input device according to the present invention can be used as a normal image scanner, and has the effect of providing a device that also functions as a coordinate input device.

〔Effect of the invention〕

As described above, the coordinate input device according to the present invention includes a one-dimensional image sensor, a rotating scanning mirror that sequentially sends images of a subject and a pointing device on the subject to the one-dimensional image capturing element, and a rotating scanning mirror that rotates to sequentially send images of a subject and a pointing device on the subject to the one-dimensional imaging device. A detector that detects the rotation angle, a controller that specifies the rotation angle and narrows down the scanning range to a specific area including the point indicator, and stores the output image signal of the one-dimensional image sensor at an address corresponding to the rotation angle. The image processing apparatus includes an image memory and an image processing device that processes the image signal to detect the position coordinates of the point pointing tool, and the position of the point pointing tool on the subject is determined based on the detection signal. Therefore, compared to the conventional coordinate input device using a TV camera, it is possible to obtain a device that can input coordinates at high speed and with high resolution.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a coordinate input device according to an embodiment of the invention, FIG. 2 is an explanatory diagram showing an imaging operation in the coordinate input device according to an embodiment of the invention, and FIG. Explanatory diagram showing the coordinate input operation in the coordinate input device according to the embodiment, 4th
FIG. 5 is a flowchart showing the operation of the controller according to an embodiment of the present invention, FIG. 5 is an explanatory diagram showing image processing for coordinate input operation of the coordinate input device according to the embodiment of the present invention, and FIG. 1 is a schematic configuration diagram showing a conventional coordinate input device. In the figure, 1 is a lens, 2 is a rotating scanning mirror, 3 is a driving device, 4 is a one-dimensional image sensor, 5 is a detector, and 6
1 is a controller, 7 is an image memory, 8 is a display device, 9 is an image processing device, 10 is a subsampling circuit, 11 is a reading document, and 12 is a writing pen. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A one-dimensional image sensor, a rotating scanning mirror that sequentially sends images of a subject and a pointing device on the subject to the one-dimensional image capturing device, and a detection device that detects the rotation angle of the rotating scanning mirror. a controller that specifies the rotation angle and narrows down the scanning range to a specific area including the point indicator, an image memory that stores the output image signal of the one-dimensional image sensor at an address corresponding to the rotation angle, and the image A coordinate input device comprising an image processing device that processes a signal to detect the positional coordinates of the pointing tool, and determines the position of the pointing tool on the subject based on the detection signal. 2. The coordinate input device according to claim 1, wherein the controller has a function of determining a specific area to be scanned next according to the position of the pointing tool and tracking the movement of the pointing tool. 3. The coordinate input device according to claim 1 or 2, wherein the controller changes the resolution by changing the step size of the rotation of the rotating scanning mirror. 4. The image forming apparatus according to any one of claims 1 to 3, comprising a sub-sampling circuit, which reduces the number of pixels of an output image signal of a one-dimensional image sensor to a predetermined resolution and stores the resulting image signal in an image memory. Coordinate input device.