Optical touch system and image processing method thereof

Abstract

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.

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:
 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:   
       
         
           
             
               
                 M 
                 
                   i 
                   + 
                   1 
                 
               
               = 
               
                 
                   
                     1 
                     - 
                     MTF 
                   
                   
                     1 
                     + 
                     MTF 
                   
                 
                  
                 
                   M 
                   i 
                 
               
             
           
         
         where M i  represents an intensity value on the i-th iteration and K i+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.