OPTICAL TOUCH SYSTEM AND IMAGE PROCESSING METHOD THEREOF
An optical touch system includes an image sensor module and a processor. The image sensor module includes a plurality of image sensing elements that can be independently controlled to achieve different exposure times. The plurality of image sensor elements can produce a picture including a plurality of pixel groups. The processor is configured to extract an intensity value of each pixel group and to select a set of successive pixel groups as an object image according to the intensity values of the pixel groups.
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The present application is based on, and claims priority from, Taiwan Patent Application Serial Number 100121547, filed on Jun. 21, 2011, the disclosure of which is hereby incorporated by reference herein in its entirety.
BACKGROUND1. Technical Field
The present invention relates to an optical touch system and an image processing method thereof.
2. Related Art
An optical touch system generally comprises an imaging device, an illuminating device, and a computing device for determining the touch position of an object. Typically, the object may be a finger, a stylus, or the like. The imaging device is configured to view a touch zone above a touch surface. The illuminating device is configured such that when an object is in the touch zone, the illuminating device can make the object generate an identifiable contrast image on a picture produced by the imaging device. The computing device is configured to calculate the coordinates of the object according to the brightness variation of the picture produced by the imaging device.
The optical touch system can be designed as a system in which the object entering into the touch zone blocks the light projected from the illuminating device so as to form a dark area on the imaging device, or as a system in which the object reflects the light projected from the illuminating device to form a bright area. Regardless of which system is employed, the current coordinate calculating method requires two pictures, a background picture and a picture taken when there is an object in the touch zone. Normally, the background picture is generated and stored before operation. The optical touch system can identify the region having obviously different intensity by comparing the captured picture and the background picture. When the region having obviously different intensity is used as an image formed by an object, the optical system can calculate the coordinates of the object according to some features of the region having obviously different intensity.
In addition to the region having obviously different intensity, the intensity levels of a portion of the background area of the picture may be changed due to the change of the light path or the manner of light reflection of the touch surface caused by the object such that a difference may occur between a background area of the picture and the corresponding portion of the background picture. Such difference may make it impossible for the region having obviously different intensity to be correctly calculated or properly identified. As a result, the coordinates of the object cannot be accurately calculated.
SUMMARYOne embodiment provides an image processing method and an optical touch system using the same. The image processing method can use a single picture to determine the coordinates of an object such that incorrect coordinates will not be obtained when there is a difference between a background area of a picture and the corresponding portion of a background picture.
In one embodiment, an optical touch system comprises an image sensor module and a processor. The image sensor module comprises a plurality of image sensing elements. The image sensing elements are configured to be independently controlled to achieve different exposure times. The plurality of image sensing elements may generate a picture comprising a plurality of pixel groups. The processor is configured to extract an intensity value representing each pixel group. The processor is also configured to select a portion of the pixel groups as an object image according to the intensity values of the pixel groups.
In one embodiment, an image processing method of an optical touch system comprises obtaining a picture comprising a plurality of first pixel groups, determining a plurality of first difference values each determined by subtracting intensity values of two of the plurality of first pixel groups, and selecting a set of successive pixel groups as an object image according to the first difference values.
To better understand the above-described objectives, characteristics and advantages of the present invention, embodiments, with reference to the drawings, are provided for detailed explanations.
The invention will be described according to the appended drawings in which:
The following description is presented to enable any person skilled in the art to make and use the disclosed embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the disclosed embodiments. Thus, the disclosed embodiments are not limited to the embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein.
The image processing method of one embodiment of the present invention can be applied using an illumination-compensated picture whose image intensity variation is compensated for and with a normally captured picture whose image intensity variation is not compensated for. The description below begins by describing application of the image processing method of one embodiment of the present invention to an illumination-compensated picture.
The method of compensating for image intensity variation can be implemented as software or hardware means and is applicable to a picture to increase the intensity of the portion that originally has lower intensity and to reduce the intensity of the portion that originally has higher intensity, so as to obtain a new picture with uniform intensity. For example, as shown in
As illustrated in
The adjustment value is used to compensate for the variation of an intensity fluctuating pattern. The adjustment value can be determined through many methods, one of which is illustratively demonstrated herein. In one embodiment, an adjustment value can be obtained by the following steps: A background picture is generated using a fixed exposure time. Next, an intensity value (In) of each pixel group is determined. Finally, a ratio of a target intensity value (IT) to the intensity value (Ip) for each pixel group is calculated, wherein the ratio (Ip/IT) can be used as an adjustment value.
The compensation for the intensity variation of the picture can be achieved through hardware. As illustrated in
Referring to
The exposure time for controlling the electronic shutter 411 of each image sensing element 41a or 41b can be obtained using the following method; however, the present invention is not limited to such method. The method obtains a background picture by a fixed exposure time. Next, the intensity value of each pixel of the background picture is extracted. Thereafter, the exposure time that is needed for operating the corresponding electronic shutter 411 of an image sensing element 41a or 41b and can make the corresponding pixel achieve a target intensity level is computed using the target intensity level and the intensity value of the pixel.
D1(pi)=I(pi)−T1 (1)
At Step S55, a threshold Th1 is used to determine a section R1 of the intensity fluctuating pattern I(p) that includes pixel groups having ratios of difference values D1(pi) to the target intensity value T1 less than or greater than the threshold Th1 as an object image.
In particular, compared with the method of calculating the difference value of two adjacent pixel groups (pi and pi+1), the method of calculating the difference value between a pixel group pi and a pixel group pi+q+1 that are spaced at a predetermined number q can obtain larger difference values at the edges of the object image 121. As shown in
The predetermined number q can be a user set number, or a value determined by the modulation transfer function (MTF) of the image sensor module 11, wherein the MTF is a measure of the transfer of modulation (or contrast) from an object to an image. An MTF value can be a point on a MTF curve or an average of points on an MTF curve. From a background picture, a pixel group is selected and an initial intensity value Mo representing the pixel group is extracted. The following equation (2), an MTF value, and the initial intensity value Mo are used to determine the to number of iterations needed when a last iterated result is less than a predetermined value, wherein the number of iterations can be used as the number q.
The description below is related to an image processing method that is applicable to a normally captured picture whose image intensity variation is not compensated for.
At Step S144, a minimum of the difference fluctuating pattern BSD(p) is then determined as a threshold Th6, and a maximum of the difference fluctuating pattern BSD(p) is determined as a threshold Th7. A Step S145, a picture comprises a plurality of pixel groups arranged along a direction obtained. At Step S146, an intensity value I(pi) representing each pixel group of the picture is extracted to obtain an intensity fluctuating pattern I(p) as shown in
The data structures and code described in this detailed description are typically stored on a non-transitory computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The non-transitory computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing code and/or data now known or later developed.
The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a non-transitory computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the non-transitory computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the non-transitory computer-readable storage medium. Furthermore, the methods and processes described below can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalent.
Claims
1. An optical touch system comprising:
- an image sensor module comprising a plurality of image sensing elements configured to be independently controlled to achieve different exposure times, the plurality of image sensing elements generating a picture comprising a plurality of pixel groups; and
- a processor configured to extract an intensity value representing each pixel group and select a portion of the pixel groups as an object image according to the intensity values of the pixel groups.
2. The optical touch system of claim 1, wherein the picture is an illumination-compensated picture.
3. The optical touch system of claim 1, wherein each pixel group comprises a plurality of pixels, wherein the intensity value representing each pixel group is a sum or an average of intensity values of the pixels of the pixel group.
4. The optical touch system of claim 1, wherein each pixel group is a line of pixels.
5. The optical touch system of claim 1, wherein the processor is configured to subtract a threshold value from the intensity value representing each pixel group to obtain a plurality of difference values and to select the portion of the pixel groups according to ratios of the difference values to the threshold value.
6. The optical touch system of claim 1, wherein the portion of the pixel groups is greater or smaller than a threshold value.
7. The optical touch system of claim 5, wherein the threshold value is an average of the intensity values representing the pixel groups or a predetermined value.
8. The optical touch system of claim 1, wherein the image sensor module is configured to generate a background picture using a fixed exposure time and use an intensity value of the background picture corresponding to each pixel group to adjust the exposure times of corresponding image sensing elements.
9. The optical touch system of claim 1, wherein the image sensor module is configured to adjust the exposure time for each image sensing element to allow the image sensor module to generate a new background picture comprising a plurality of pixel groups having intensity values within an intensity range.
10. An image processing method of an optical touch system, comprising the steps of:
- obtaining a picture comprising a plurality of first pixel groups;
- is determining a plurality of first difference values each determined by subtracting intensity values of two of the plurality of first pixel groups; and
- selecting a set of successive pixel groups as an object image according to the first difference values.
11. The method of claim 10, wherein the picture is an illumination-compensated picture.
12. The method of claim 10, wherein the step of determining a plurality of first difference values comprises a step of determining a first difference value between the intensity values of each two adjacent ones of the plurality of first pixel groups.
13. The method of claim 10, wherein the step of determining a plurality of first difference values comprises a step of determining a first difference value between the intensity values of a pair of first pixel groups separated by an interval of a predetermined number.
14. The method of claim 13, wherein the predetermined number is determined by the steps of: M i + 1 = 1 - MTF 1 + MTF M i
- obtaining an MTF value of an image sensor;
- selecting the intensity value of one of the first pixel groups as an initial intensity value;
- using the following equation, the MTF value and the initial intensity value to determine a number of iterations needed when an iterated result is less than a predetermined value:
- where Mi represents an intensity value on the i-th iteration and Ki+1 represents an iterated result on the i-th iteration; and
- selecting the number of iterations as the predetermined number.
15. The method of claim 10, further comprising the steps of:
- determining, from the plurality of first pixel groups, a first boundary pixel group corresponding to the first difference value less than a first threshold value;
- determining, from the plurality of first pixel groups, a second boundary pixel group corresponding to the first difference value greater than a second threshold value; and
- selecting a plurality of ones of the pixel groups between the first and second boundary pixel groups as the object image.
16. The method of claim 15, further comprising the steps of:
- obtaining a background picture that comprises a plurality of second pixel groups;
- determining a plurality of second difference values each determined by subtracting intensity values of two of the plurality of second pixel groups;
- selecting a minimum from the second difference values as the first threshold value; and
- selecting a maximum from the second difference values as the second threshold value.
17. The method of claim 10, wherein each first pixel group comprises a plurality of pixels, and the intensity value representing each pixel group is a sum of intensity values of the pixels of the pixel group.
18. The method of claim 10, wherein the pixel group is a line of pixels.
Type: Application
Filed: Jun 13, 2012
Publication Date: Dec 27, 2012
Applicant: Pixart Imaging Inc. (Hsin-Chu)
Inventors: Tzung Min SU (Hsinchu City), Ren-Hau Gu (Hsinchu City), Chih Hsin Lin (Hsinchu City), Cheng Nan Tsai (Hsinchu City)
Application Number: 13/495,712
International Classification: G06F 3/042 (20060101);