Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. Provisional Application Ser. No. 60/217,821, filed Jul. 12, 2000, the full disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a method of pixel address detection of an image sensor having windowing function. More particularly, the present invention relates to a method of defective pixel address detection of an image sensor having windowing function. 
     2. Description of Related Art 
     As the multimedia era is coming, digital information, such as digital images or digital movies, becomes more popular. Modem technology has highly developed, and the cost of image sensors for generating digital images or pictures reduces. More people can access these high technological products. However, there are still some problems about the image sensors. 
     Due to the current process, it is hard to fabricate an image sensor perfectly without any bad or defective pixel thereon. Therefore, there are always some defective pixels on the image sensor after it is fabricated. The image or picture sensed by the defective pixels will affect the quality of the image or picture. And the following imaging procedure, such as color processing or image compressing etc, will also affected. How to ship the defective pixels of the image sensor becomes a significant topic. 
     The method for solving such problems can be restoring a set of defective pixel addresses first. And then the pixels of the image sensor are read in sequence to compare with the defective pixel addresses, by which the defective pixels can be detected while the image sensor operates. However, if the image sensor has a window function, the pixels of the image sensor are not sensed in sequence, but from one pixel address to another non-consecutive pixel address. If the non-consecutive pixel address is larger than the currently indexed memory element contents, there is not a hit. The index is struck and not moving under this condition. The detection for the defective pixel addresses fails to function. 
     To solve these problems, according to conventional schemes, a more complicated algorithm or another tag bit in a memory element is used. However, the conventional methods increase the cost of the image sensor due complexity and increasing size of the image sensor. 
     SUMMARY OF THE INVENTION 
     The invention provides a method of defective pixel address detection for an image sensor. A plurality of defective pixel addresses are stored first during the image sensor is tested. A pixel address of the image sensor is read and one of the defective pixel addresses is fetched. The first fetched defective pixel address is compared with the pixel address of the sensor address, and then a defective pixel flag is outputted if the pixel address is equal to the defective pixel address. An index value is increased by one unit and another defective pixel address which is indexed next to the first fetched defective pixel address is fetched. The first fetched defective pixel address is compared with the pixel address of the sensor address and further determines the index value if the pixel address is not equal to the defective pixel address. The index value is increased by one unit and fetching another defective pixel address which is indexed next to the first fetched defective pixel address if the pixel address of the sensor address is larger than the first fetched defective pixel address and the index is not equal to zero. Determine whether a frame begins if the pixel address of the sensor address is not larger than the first fetched defective pixel address or the index is equal to zero. The index value is increased by one unit and fetching another defective pixel address which is indexed next to the first fetched defective pixel address if the pixel address of the sensor address is larger than the first fetched defective pixel address and the index is not equal to zero and the frame begins. 
     The defective pixel address is compared with an empty signature if the pixel address of the sensor address is not larger than the first fetched defective pixel address and the index is not equal to zero and no frame begins. The index value is increased by one unit if the defective pixel address is the empty signature, and then fetching another defective pixel address which is indexed next to the first fetched defective pixel address; and fetching another defective pixel address which is indexed next to the first fetched defective pixel address if the defective pixel address is not the empty signature. 
     Advantageously, the present invention provides an effective and efficient method for determining whether the pixel of the image sensor is defective, by which the following color processing and image compression etc can be significantly simplified. In addition, the method of defective pixel address detection for an image sensor is in a simple and low cost way. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 schematically shows a block diagram for carrying out the method of the present invention; 
     FIG. 2 illustrates a schematic diagram of the format of the memory element for storing the defective pixel addresses having a windowing range according to conventional method; 
     FIG. 3 illustrates a schematic diagram of the format of the memory element for storing the defective pixel addresses having a windowing range according to one preferred embodiment of this invention; and 
     FIG. 4 schematically shows a flow chart of the method of defective pixel address detection for image sensor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically shows a block diagram for carrying out the method of the present invention. The circuit of defective pixel address detection for image sensor comprises at least a memory element  10  and an address comparator  20 . The memory element  10  is used for storing the defective pixel addresses which are detected during the image sensor is tested. The memory element  10  can be a fuse array, for example. The address comparator  20  receives a current sensor address of the image sensor Sensor_addr and fetches a defective pixel address Def_pixel_addr from the memory element  10 . The address comparator  20  then compares the two addresses Sensor_addr and Def_pixel_addr. If the two addresses, Sensor_addr and Def_pixel_addr, are the same, which means a hit, the address comparator  20  generates a flag bit F to indicate that the current sensor address of the image sensor is a defective pixel. The index of the memory element  10  is increased by one unit, such as 1, to begin another cycle of address comparison. If the two addresses, Sensor_addr and Def_pixel_addr, are not the same, which means a miss, the address comparator  20  sets the flag bit F to a value, such as 0, to indicate that the current sensor address of the image sensor is a good pixel. And then another cycle of address comparison is begun. 
     When the image sensor has a windowing function, the pixels of the image sensor are not sensed in sequence, but from one pixel address to another non-consecutive pixel address which forms a windowing range. If the non-consecutive pixel address is larger than the contents of the currently indexed memory element, there is not a hit for the currently indexed memory element contents. Namely, the index is struck and not moving under this condition. The detection for the defective pixel addresses fails to function. FIG. 2 shows the situation. 
     FIG. 2 illustrates a schematic diagram of the format of the memory element for storing the defective pixel addresses having a windowing range according to conventional method. As shown in FIG. 2, the windowing range  10 ′ only includes those addresses from index  5  to index  125 . For those defective pixel addresses outside the windowing range  10 ′, there is no hit and the index does not move under the condition. In the case, the index stays at location  0  and does not move because there is not any hit for the address at index  0 . In other words, the defective pixel address detection fails when the image sensor is in the window mode. 
     For solving the window function with a minimum cost, two properties of the contents of the memory element  10  are provided. First, the defective pixel addresses stored in the memory element  10  is in an ascending order; and second, the currently indexed contents are always larger than or equal to the current sensor address to have a hit condition. In the window mode, the pixel address of the image sensor jumps from on pixel address to another non-consecutive pixel address, which is larger than the contents of the currently indexed memory element  10 . A hit flag is generated for making its index move to the next position. 
     Therefore, after several cycles, the index of the memory element  10  is pointed to the contents which are larger than or equal to the current pixel address of the image sensor. 
     FIG. 3 shows the situation. 
     As shown in FIG. 3, when the address jumps from address  0000 _ 0000 _ 0000 _ 0000 _ 0000  to the window starting address  0000 _ 0000 _ 0000 _ 0001 _ 0000  of the windowing range  10 ′, the address comparator  20  (shown in FIG.  1 ,) detects that the indexed defective pixel address  0000 _ 0000 _ 0000 _ 0000 _ 1001  is less than the current image sensor address. The address comparator  20  forces the index to move from index  0  to index  1  by generating a hit flag. After two more clock cycles, the index is at index  4  which is within the windowing range  10 ′. Therefore, the index is not struck and detection for the defective pixel addresses still functions well. 
     Furthermore, when the index wraps around to the beginning and the pixel address of the image sensor has not reached the end of the current frame, a special scheme is needed because the current pixel address of the image sensor is large than the indexed contents of the memory element  10 , and the index is not needed to be increased at this time. The large-than comparison method for the index at the beginning of the memory element  10  must wait until the current pixel address of the image sensor wraps around and begins with (0,0). 
     Silo In addition, if the number of the defective pixel addresses is less than that of the memory element  10 , empty signatures are put in the remained locations of the memory element  10 . The index moves to the next position when the empty signature is detected. The index finally wraps around to the beginning of the memory element  10 . And in the next frame, the defective pixel address detection begins. 
     Referring to FIGS. 4 and 1, according to the embodiment of the present invention, after an image sensor is fabricated, the image sensor is tested for finding defective pixels on the image sensor. The detected defective pixel addresses are then stored into the memory element  10  in an ascending order. The memory element  10  further comprises an index for indicating the current fetched defective pixel address, which as shown in FIG.  3 . 
     As the image sensor operates, a reset step is performed, by which the index of the memory element  10  indicated the first location that will be fetched first as following, and the image sensor is set to the first pixel waiting for sensing. 
     When the sensing process begins, the pixel addresses of the image sensor are read in a windowing way. After one pixel address of the image sensor is read by the address comparator  20 , the address comparator  20  further fetches a defective pixel address indicated by the index  0  from the memory element  10 . 
     As shown in FIG. 4, the step S 100  is then performed. The address comparator  20  receives the pixel address of the image sensor Sensor_addr and the defective pixel address Def_pixel_addr, and compares the two addresses. If the address Sensor_addr hits the address Def_pixel_addr, which means the same, the step S 102  is performed. Namely, the address comparator  20  outputs a defective pixel flag F for indicating the current pixel of the image sensor is a defective or bad pixel. 
     After the defective pixel flag F is outputted, the step S 104  is performed to increase the index of the memory element  10  by one, for example index  1  as shown in FIG.  3 . After the index is increased by one, another address comparison cycle begins. Namely, the address comparator  20  read another pixel address of the image sensor and next defective pixel address indicated by index  1 . 
     In the S 100  of the address comparison, if the addresse Sensor_addr misses the address Def_pixel_addr, which means not the same, the step S 106  is performed. 
     At the step S 106 , if the address Sensor_addr is greater than the address Def_pixel_addr and the index is not equal to 0, the step  104  is performed to increase the index of the memory element  10  by one. After the index is increased by one, another address comparison cycle begins. The process returns to the step S 100 . Namely, the address comparator  20  read another pixel address of the image sensor and next defective pixel address. In addition, if the address Sensor_addr is not greater than the address Def_pixel-addr or the index is not equal to 0, the step S 108  is performed. 
     At the step S 108 , if the address Sensor_addr is greater than the address Def_pixel_addr and the index is not equal to 0 and a new frame begins, the step  104  is performed to increase the index of the memory element  10  by one. After the index is increased by one, another address comparison cycle begins. The process returns to the step S 100 . Namely, the address comparator  20  read another pixel address of the image sensor and next defective pixel address. In addition, if the address Sensor_addr is not greater than the address Def_pixel_addr or the index is not equal to 0 or no new frame begins, the step S 110  is performed. 
     At the step S 110 , whether the address Def_pixel_addr is an empty signature is determined. The empty signature, for example, has a format of  1111 _ 1111 _ 1111 _ 1111 _ 1111 . When the empty signature is detected, the index is forced to be increased by one. Namely, the empty signature of the defective pixel address is detected, the step S 104  is performed to increase the index by one. After the index is increased by one, another address comparison cycle begins. Namely, the step S 100  is performed and the address comparator  20  read another pixel address of the image sensor and next defective pixel address. 
     Furthermore, at the step S 36 , if the defective pixel address is not an empty signature, the procedure returns to the step S 100 . The address comparator  20  read another pixel address of the image sensor and next defective pixel address. 
     Accordingly, the present invention provides an effective and efficient method for determining whether the pixel of the image sensor is defective during operation of the image sensor. The following color processing and image compression etc can be significantly simplified. In addition, the method of defective pixel address detection for image sensor is in a simple and low cost way. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Technology Category: 5