the detailed embodiment of this invention will be introduced referring to the figures provided in the following . in additional , all the information embedding codes are recorded as bar halftone screen codes except two dimensional halftone screen code in this embodiment . first of all , it is worth defining all the terms in this embodiment . fig1 is a sketch map showing an implementation of am and fm halftone screen . ( a ) an example of an am halftone screen . ( b ) an example of a fm halftone screen . dot 101 is the smallest printing unit which is a kind of color printed on picture element 102 . halftone dot is the smallest unit of an image . the am halftone screen given in fig1 ( a ) represents the grayscale by the size of the halftone dots . the fm halftone screen given in fig1 ( b ) represents the grayscale based on the density of the halftone dots . in this embodiment , am and fm halftone screen are defined as a method of generating halftone dots with different modulations . the definition of halftone screen code : at least one of the forms ( image , text , symbol and background ) is targeted to be printed onto the recordable media , wherein the printed content comprises at least one pixel , and can be replaced by a predetermined array of halftone dots with different morphology including physical and geometrical characteristics according to the information embedded method that the same pixel morphology are exchangeable . the halftone screen code of embedding information into print content is achieved as above . the characteristic of this embedding information method is that the calculated maximum similarity value between codes is lower than the threshold value . fig2 is an embodiment of halftone dots used . ( a ) an example of a concentrated halftone screen . ( b ) an example of a scattered halftone screen . as shown in fig2 ( a ), so - called concentrated halftone dot refers to that all the dot - matrix within a halftone dot is concentrated at one point . as shown in fig2 ( b ), so - called scattered halftone dot means that at least one bit of the dot - matrix within a halftone dot is separated from the others . in addition , concentrated halftone dots can be grouped as a kind of am halftone screen and scattered halftone screen can be grouped as a kind of fm halftone screen . in this embodiment , concentrated halftone dots are considered to be generated by am halftone screen and scattered halftone dots are generated by fm halftone screen . as shown in fig3 , a hexadecimal bar halftone screen code can be generated by concentrated halftone dots and scattered halftone dots in fig3 , 301 represent scattered halftone dots , and 302 represents concentrated halftone dots . in addition , c n represents the code value . when scattered and concentrated halftone_dots are grouped together , the consistent grayscale can be obtained , and code value could be represented as well . here , the code value c k , c 0 to c m − 1 ( m is the number of the codes , supposed to be 16 ) is defined as an assembly of halftone screen code arrayed as a predetermined order . the characteristic of this assembly of halftone screen code is that the maximum similarity value is guaranteed to be under the threshold value while describing the grayscale . in this embodiment b i , k represents the k th bit of code i . as shown in fig3 , all the halftone dots of code 0 ( c 0 ) are formed by scattered halftone dots . b 1 , 0 , b 1 , 1 , b 1 , 2 , b 1 , 3 , b 1 , 4 , b 1 , 5 , b 1 , 6 , b 1 , 7 are formed by concentrated halftone dots . b 1 , 8 , b 1 , 9 , b 1 , 10 , b 1 , 11 , b 1 , 12 , b 1 , 13 , b 1 , 14 , b 1 , 15 are formed by scattered halftone dots . also , b 2 , 0 , b 2 , 1 , b 2 , 2 , b 2 , 3 , b 2 , 12 , b 2 , 13 , b 2 , 14 , b 2 , 15 from code 2 ( c 2 ) are concentrated halftone dots . b 2 , 4 , b 2 , 5 , b 2 , 6 , b 2 , 7 , b 2 , 8 , b 2 , 9 , b 2 , 10 , b 2 , 11 are formed by scattered halftone dots . from code 3 ( c 3 ) to code f ( c f ) as shown in fig3 , are formed by concentrated and scattered halftone dots . also , in code 0 ( c 0 ) and code f ( c f ), code 1 ( c 1 ) and code e ( c e ), code 2 ( c 2 ) and code d ( c d ), code 3 ( c 3 ) and code c ( c c ), code 4 ( c 4 ) and code b ( c b ), code 5 ( c 5 ) and code a ( c a ), code 6 ( c 6 ) and code 9 ( c 9 ), and code 7 ( c 7 ) and code 8 ( c 8 ), the scattered halftone dots are in the reciprocal position to concentrated halftone dots . as shown in fig3 , the numbers of scattered halftone dots and the concentrated halftone dots are the same . as a result , the parity check could be conveniently achieved without parity bit , realizing high efficient recording . accordingly , the maximum similarity value between the codes of the halftone screen code shown in fig3 is calculated in the following . first of all , suppose ck to be the code value of the bar halftone screen code , and suppose the bits of ck as all elements . here , the bits are formed by concentrated and scattered halftone dots . then , suppose the total number of bits as the length of the code . fig3 indicates that the code length of this example is 16 . fig4 shows the calculation method of calculating the maximum similarity value between the bar halftone screen . an example of calculating the distance between the codes from the halftone screen code is further illustrated in fig4 . the calculation is to obtain the distance between 4 ( c 4 ) and 5 ( c 5 ). ( 1 ) first of all , a logical nonequivalence sum between codes is calculated according to [ equation 5 ]. ( 2 ) afterwards , logical nonequivalence sums are added up to obtain a distance between the codes in this claim according to the [ equation 6 ]. the distance between code 4 ( c 4 ) and code 5 ( c 5 ) in the example above is calculated as 8 . as shown in equation 11 , the distance between codes in fig3 can be calculated . the minimum distance is found from all the data of distance between codes . and then , the maximum similarity value can be calculated according to [ equation 6 ]. fig3 shows the maximum similarly value between the codes of the bar halftone screen code to be ½ . fig5 illustrates the relationship between the grayscale and the number of the dots within the halftone . dot referring to fig5 ( a ) is an example of a concentrated halftone dot with a grayscale value of 3 ; ( b ) is an example of a scattered halftone dot with a grayscale value of 3 ; ( c ) is an example of a concentrated halftone dot with a grayscale value of 4 ; ( d ) is an example of a scattered halftone dot with a grayscale value of 4 ; ( e ) is an example of a concentrated halftone dot with a grayscale value of 5 ; ( f ) is an example of a scattered halftone dot with a grayscale value of 5 ; ( g ) is an example of a concentrated halftone dot with a grayscale value of 6 ; ( h ) is an example of a scattered halftone dot with a grayscale value of 6 . as shown in fig5 , there are 3 dots within one halftone dot when the grayscale value is 3 . there are 4 dots within one halftone dot when the grayscale value is 4 . there are 5 dots within one halftone dot when the grayscale value is 5 . there are 6 dots within one halftone dot when the grayscale value is 6 . in this embodiment here , the grayscale value of am halftone screen and fm halftone screen is varied correspondingly with respect to the quantity of the dots therefore , once the quantity of the dots within halftone dot is set , the grayscale performance would be manageable . as shown in fig6 , code 5 ( c 5 ) from the bar halftone screen code in fig3 can be represented as another bar halftone screen code with varied grayscale . fig6 ( a ) is an example of a bar halftone screen code with a grayscale value of 3 . ( b ) is an example of a bar halftone screen code with a grayscale value of 4 . ( c ) is an example of a bar halftone screen code with a grayscale value of 5 . ( d ) is an example of a bar halftone screen code with a grayscale value of 6 . fig6 is similar to fig5 , that there are 3 dots within one halftone dot when the grayscale value is 3 , 4 dots within one halftone dot when the grayscale value is 4 , 5 dots within one halftone dot when the grayscale value is 5 , and 6 dots within one halftone dot when the grayscale value is 6 . the embodiment uses the halftone dot - matrix arraying method as shown in fig2 to form the bar halftone screen code . it is not that the embodiment is not limited to this one type of bar halftone screen code . accordingly , a bar halftone screen code could be established as long as two or more different forms of halftone dot are present . for example , halftone dot with at least two different types of geometric forms can form a bar halftone screen code , and halftone dot with at least two different types of physical forms can form a bar halftone screen code as well . in addition , not only dot halftone screen has the described characteristics , halftone screen code can also be formed by myrialine halftone screen . as shown in fig7 , a plurality of dot geometrical distributing forms for forming the bar halftone screen code are illustrated . example ( a ) and ( b ) utilize the dot within one graphic but consisting of dot - matrix of different directions . example ( c ) utilizes the dot consisting of dot - matrix of varied shape . example ( e ) and ( f ) utilize the dot consisting of dot - matrix of varied size , wherein the grayscale of the respective halftone dot is calculated by a mean value of neighboring dot . example ( g ) and ( h ) utilize the dot having different positions but consisting of dot - matrix of same shape . it is noted that except example ( e ), the grayscale value in above fig7 are defined as 4 . in fact , any grayscale value would be appropriate in this case . as shown in fig7 ( a ) and ( b ), the bar halftone screen code can be formed by the halftone dots which are made up of dot - matrix with different directions in the same graph . as shown in fig7 ( c ) and ( d ), the bar halftone screen code can be formed by the halftone dots which are made up of dot - matrix with different shapes . as shown in fig7 ( e ) and ( f ) the bar halftone screen code can be formed by the halftone dots which are made up of dot - matrix with different sizes . as shown in fig7 ( g ) and ( h ), the bar halftone screen code can be formed by the halftone dots which are made up of dot - matrix with the same shapes but different positions . fig8 gives examples of bar halftone screen code using halftone dots with different dot - matrix distribution as described in fig7 . the bar halftone screen code shown in fig8 ( a ) is bar halftone screen code formed by halftone dots given in fig7 ( a ) and ( b ). the bar halftone screen code shown in fig8 ( b ) is formed by the halftone dots given in fig7 ( c ) and ( d ). the bar halftone screen code shown in fig8 ( c ) is formed by halftone dots given in fig7 ( e ) and ( f ). the bar halftone screen code shown in fig8 ( d ) is formed by the halftone dots given in fig7 ( g ) and ( h ). the code values of the bar halftone screen code in all the examples are set to be 5 ( c 5 ). the bar halftone screen code shown in fig8 ( a ) is formed by halftone dots which are made up of dot - matrix with different directions in the same graph . the bar halftone screen code shown in fig8 ( b ) is formed by halftone dots which are made up of dot - matrix with different shapes . the bar halftone screen code shown in fig8 ( c ) is formed by halftone dots which are made up of dot - matrix with different sizes . the bar halftone screen code shown in fig8 ( d ) is formed by halftone dots which are made up of dot - matrix with different the same shapes but different positions . the bar halftone screen code shown in fig8 ( a ) is formed by halftone dots which are made up of dot - matrix with different directions in the same graph . the bar halftone screen code shown in fig8 ( b ) is formed by halftone dots which are made up of dot - matrix with different shapes . the bar halftone screen code shown in fig8 ( c ) is formed by halftone dots which are made up of dot - matrix with different sizes . the bar halftone screen code shown in fig8 ( d ) is formed by halftone dots which are made up of dot - matrix with different the same shapes but different positions . in addition , fig9 gives examples of morphology of halftone dots with different physical properties . in fact , there are more than the types of morphology listed , i . e . the similar morphology are also included . fig1 shows an example of halftone screen code formed by halftone_dots which are composed by different physical morphology shown in fig9 . fig1 ( a ) is a bar halftone screen code formed by halftone dots shown in fig9 ( a ) and ( b ). fig1 ( b ) is a bar halftone screen code formed by halftone_dots shown in fig9 ( c ) and ( d ). fig1 ( c ) is a bar halftone screen code formed by halftone_dots shown in fig9 ( e ) and ( f ). fig1 ( d ) is a bar halftone screen code formed by halftone_dots shown in fig9 ( g ) and ( h ). fig1 ( e ) is a bar halftone screen code formed by halftone_dot shown in fig9 ( i ) and ( j ). the code values of the bar halftone screen code in all the examples here are also set to be 5 ( c 5 ). fig1 ( a ) is a bar halftone screen code formed by using different modulations of am halftone screen and fm halftone screen . the characteristic of this formation is that even the array of respective halftone dots is varied , the grayscale would be same and the whole code would not be affected . when information is embedded into the target image , the halftone dots with different grayscale values can be exchanged selectively according to the grayscale of the target image so as to ensure that the overall quality of the target image would not be affected after such embedding process . fig1 ( b ) is a bar halftone screen code formed by a set of assembled halftone dots having different wavelength and varied spectrum characteristics , such as different colors , infrared rays and ultraviolet rays . for example , ( c ) 401 of the fig9 ( c ) is light blue ( d ) 402 is printed with tiny halftone dots of green according to the permutation and combination of the halftone screen codes . according to the arrangement given by fig1 ( b ), information can be embedded into the image obviating the naked - eye recognition . this is one of the methods for embedding information into colored target images . fig1 ( c ) is a bar halftone screen code formed by an array of halftone dots with different frequency properties , including different grayscale values . for example , ( e ) 501 in fig9 ( e ) is a portion of the text in a binary image and at a location of ( f ) 502 , a halftone dot with a grayscale value smaller than that of 501 is set . according to the permutation and combination from fig1 ( c ), information can be embedded obviating the possibility being recognized by human naked eyes . this is one of the methods for embedding information in binary image such as text image . fig1 ( d ) is a bar halftone screen code formed by an array of halftone dots with different angles of polarization and deflection . for example , 601 in fig9 ( g ) is a halftone dot that is deflected or polarized to the left and 602 in fig9 ( h ) is a halftone dot that is deflected or polarized to the right . according to the permutation and combination of fig1 ( d ), information can be embedded for laser anti - counterfeiting label . fig1 ( e ) is a bar halftone screen code formed by an array of halftone dots with different magnetic intensities and different magnetic directions . for example , 701 and 702 in fig9 ( i ) and ( j ) are halftone dots with different magnetic directions . according to the permutation and combination of fig1 ( e ), information can be embedded for magnetic ink printing purposes . fig1 is a bar halftone screen code with a code length of 15 . as shown in fig1 , all the halftone dots from code 0 ( f 0 ) are scattered . b 1 , 0 , b 1 , 1 , b 1 , 2 , b 1 , 3 , b 1 , 4 , b 1 , 5 , b 1 , 6 , b 1 , 7 from code 1 ( f 1 ) are formed by concentrated halftone dots b 1 , 8 , b 1 , 9 , b 1 , 10 , b 1 , 11 , b 1 , 12 , b 1 , 13 , b 1 , 14 are formed by scattered halftone dots . b 2 , 0 , b 2 , 1 , b 2 , 2 , b 2 , 3 , b 2 , 12 , b 2 , 13 , b 2 , 14 from code 2 ( f 2 ) are formed by scattered halftone dots b 2 , 4 , b 2 , 5 , b 2 , 6 , b 2 , 7 , b 2 , 8 , b 2 , 9 , b 2 , 10 , b 2 , 11 are formed by concentrated halftone dots from code 3 ( f 3 ) to code f ( f f ) as shown in fig1 , the maximum similarity value of halftone screen code is 7 / 15 (& lt ; ½ ). fig1 is an example of a bar halftone screen code with a code length of 8 . the bar halftone screen code is shown in fig1 . all the halftone dots from code 0 ( g 0 ) are formed by scattered halftone dots code ( g 1 ) is formed by concentrated halftone dots b 1 , 0 , b 1 , 1 , b 1 , 2 , b 1 , 3 and scattered halftone dots b 1 , 4 , b 1 , 5 , b 1 , 6 , b 1 , 7 . code ( g 2 ) is formed by concentrated halftone dots b 2 , 0 , b 2 , 1 , b 2 , 4 , b 2 , 5 and scattered half tone dots b 2 , 2 , b 2 , 3 , b 2 , 6 , b 2 , 7 . code 3 ( g 3 ) to code f ( g f ) are formed as shown in fig1 . the maximum similarity value of the bar halftone screen code is ½ . fig1 is a bar halftone screen code with a code length of 8 . the difference between the bar halftone screen code in fig1 and fig1 is that the quantities of the concentrated halftone dots are defined as odd numbers . as shown in fig1 , only b 0 from code 0 ( h 0 ) is a concentrated halftone dot the rest are all scattered halftone dots . b 1 , 0 , b 1 , 2 , b 1 , 3 , b 1 , 4 , b 1 , 5 from code 1 ( h 1 ) are formed by concentrated halftone dots . b 1 , 1 , b 1 , 6 , b 1 , 7 are formed by scattered halftone dots b 2 , 0 , b 2 , 4 , b 2 , 5 , b 2 , 6 , b 2 , 7 from code 2 ( h 2 ) are formed by concentrated halftone dots b 2 , 1 , b 2 , 2 , b 2 , 3 are formed by scattered halftone dots . code 3 ( h 3 ) to code f ( h f ) are formed as shown by fig1 . the maximum similarity value of the bar halftone screen code is ½ . fig1 is a bar halftone screen code with a code length of 16 . the difference between the bar halftone screen code from fig1 and fig3 is that the concentrated and scattered halftone - dots are distributed symmetrically . as shown in fig1 , code 0 ( l 0 ) are formed by scattered halftone dots . b 1 , 1 , b 1 , 3 , b 1 , 5 , b 1 , 7 , b 1 , 8 , b 1 , 10 , b 1 , 12 , b 1 , 14 from code 1 ( l 1 ) are formed by concentrated halftone dots . b 1 , 0 , b 1 , 2 , b 1 , 4 , b 1 , 6 , b 1 , 9 , b 1 , 11 , b 1 , 13 , b 1 , 15 are formed by scattered halftone dots b 2 , 0 , b 2 , 2 , b 2 , 4 , b 2 , 6 , b 2 , 9 , b 2 , 11 , b 2 , 13 , b 2 , 15 from code 2 ( l 2 ) are formed by concentrated halftone dots . b 2 , 1 , b 2 , 3 , b 2 , 5 , b 2 , 7 , b 2 , 8 , b 2 , 10 , b 2 , 12 , b 2 , 14 are formed by scattered halftone dots code 3 ( l 3 ) to code f ( l f ) are formed as shown by fig1 . the code can still be decrypted even though the paper is inverted with a 180 °. the maximum similarity value of the bar halftone screen code is ½ . here , the information embedded into paper will be susceptible to two types of noise interference . the first kind of noise refers to pollution or defect on paper which can cause concentrated errors of halftone dots on a large area . such errors are known as paroxysmal errors . the second type of noise refers to the pollution from the printer drum or tiny deformation of paper due to heat , or optical quantum effects of scanner , which causes random independent errors . such errors are referred as random errors . in reality , it is easy to have large area pollution on the paper . therefore , the probability of the first type of paroxysmal noise is far more likely to happen than the second type of random errors . also , the polluted dots on the blank paper are usually treated as concentrated halftone dots . therefore , whenever the errors happened , the probability of converting concentrated halftone dots to scattered halftone dots is far lower than the probability of converting scattered halftone dots to concentrated halftone dots as a result , it is better to have more concentrated halftone dots in bar halftone screen code . fig1 is a process flow chart according to the method of generating halftone screen code of the present invention . the method comprises the following steps : ( s 3 ) selecting and generating a plurality of codes by gauging the code lengths of same value ; ( s 4 ) calculating similarity values between the plurality of codes , wherein the similarity is expressed as ( n − d )/ n , suppose d to be a distance and n to be the code length . ( s 5 ) determining whether the similarity is lower than the threshold value , wherein a typical threshold values is ½ , even ¼ . if the similarity value is higher than the threshold value ( s 5 → no ), the process is switched to ( s 7 ). if the similarity value is smaller than the threshold value ( s 5 → yes ), then turn to ( s 6 ). ( s 6 ) saving the codes with the similarity value lower than the threshold value ; ( s 7 ) determining whether the similarity comparison is completed , if it is not completed ( s 7 → no ), then go back to ( s 4 ). if all the comparisons are completed ( s 7 → yes ), then send the codes with a similarity value smaller than the threshold value as a second group to ( s 8 ) to replace halftone dots . up until now , all bits of codes are still “ 0 ” or “ 1 ” in a binary system . ( s 8 ) exchanging the binary code with halftone dots according to different morphology of the halftone dots to form a halftone screen code . in this embodiment , concentrated am halftone dots and scattered fm halftone dots as shown in fig2 are the main sources of halftone dots it is not only limited to this type of halftone dots as shown in fig7 ( a ) to ( h ), many halftone dots with different geometric characteristics can also form halftone screen code . as shown in fig9 ( c ) to ( j ), many halftone dots with different physical characteristics can also form halftone screen code . ( s 9 ) recording a target image via a scanning means to obtain an image data ; ( s 10 ) analyzing the image data to obtain a pixel analysis . ( s 11 ) sending the pixel analysis into a message embedded code . during the pixel analyzing process ( s 10 ), all morphology of pixels including its grayscale are analyzed and the result is sent to the encoding process ( s 11 ). in this embodiment the grayscale analyzing process is carried out by representing the grayscale with its pixel intensity . it is not only limited to analyzing the grayscale , it is also appropriate to analyze different morphology of colors , angles of polarization , or magnetic properties . ( s 11 ) embedding a predetermined information according to the rules of the halftone screen code ( s 12 ) replacing pixel characteristic data obtained from ( s 10 ) from encoded information ( s 13 ) using the result obtained from s 11 to exchange with pixels from the image data to arrive the aim of embedding information . a common application of the halftone screen code is listed below , wherein the physical morphology of the halftone dots of the present invention comprise different colors , i . e . different spectra , or different grayscales , i . e . different frequencies suppose n kinds of colors c 1 , c 2 , . . . , c n to be a set of color distribution of neighboring pixels in a given image , and o 1 , o 2 , . . . , o m to be another set of color distribution opposite to c 1 , c 2 , . . . , c n . if o 1 , o 2 , . . . , o m are embedded at a position adjacent to c 1 , c 2 , . . . , c n and invisible to human eyes , embedding information into color images can be achieved by the halftone screen code with c 1 , c 2 , . . . , c n representing “ 1 ” and o 1 , o 2 , . . . . , o m representing “ 2 ”. accordingly , suppose a plurality of grayscale values h 1 , h 2 , . . . , h n to be a grayscale distribution of neighboring pixels in a given image , and k 1 , k 2 , . . . , k m is another set of grayscale values against h 1 , h 2 , . . . , h n . the encoding can be finished by representing h 1 , h 2 , . . . , h n as “ 1 ” and k 1 , k 2 , . . . , k m as “ 2 ”. a special example is to set h 1 , h 2 , . . . , h n to be the highest grayscale values , and k 1 , k 2 , . . . , k m to have at least one type of grayscale value below the highest grayscale value . therefore , the halftone screen code can be applied to embed information for binary image . according to the present invention , the bar halftone screen code is capable of forming a 2 - dimensional halftone screen code representing more than one code inside one halftone dot . as shown in fig1 , a halftone screen code with a code length of 16 is divided into four sections to form a 2 - dimensional halftone screen code with a 4 * 4 dot - matrix as shown in fig1 . the maximum similarity value between codes of the new 2 - dimensional halftone screen code is the same as the original bar halftone screen code . the following embodiment shows a bar halftone screen code wherein massive information can be embedded into the background of the image . the sample is a receipt . as shown in fig1 , contents , quantities , unit prices , and total price are represented by a symbol *. the real data are embedded into the background of the receipt so that information can be kept safely even though the receipt is lost . at the same time , data embedded on the receipt can be scanned and entered into a computer . although massive halftone screen codes are embedded into the background of the receipt , it is almost impossible to identify with human eyes because the size of the halftone dot is extremely small . the embodiment and the example for comparison are executed as the following terms . the code lengths of the embodiment and the compare example are both 16 . the number of halftone dots for the experiment is 1600 . these halftone dots are embedded into the paper by bar halftone screen code . five experiments are performed . in every experiment , interference from noises is added into the said halftone dots according to the given random values . when interfered , the halftone dots representing 1 will keep their original values and those representing 0 will change their original values , because the halftone dots represent 1 when polluted on the paper . therefore , in the embodiment below , concentrated halftone dots will remain the same when interfered , but scattered halftone dots will become concentrated halftone dots when interfered . in addition , the error rates as the experiment results refer to the percentage of incorrect recognition of the halftone screen codes embedded on the paper by the detecting device . table 1 gives the error rates of the example for comparison . 1100110011001100 and 0011110011001100 , with a similarity value between codes equals to ¾ , are repeatedly embedded . at the same time , the detecting error rates are calculated for 160 halftone dots with 10 % interference , 320 halftone dots with 20 % interference and 640 halftone dots with 40 % interference . and the results are listed in the following table with units in %. table 2 gives the error rates of the implementation example . 1100110011001100 and 0011110011001100 , with a similarity value between codes equals to ½ , are repeatedly embedded . at the same time , the detecting error rates are calculated for 160 halftone dots with 10 % interference , 320 halftone dots with 20 % interference and 640 halftone dots with 40 % interference . and the results are listed in the following table with units in %. table 3 gives the error rates of the implementation example . 1100110011001100 and 0011110011001100 , with a similarity value between codes equals to ¼ , are repeatedly embedded . at the same time , the detecting error rates are calculated for 160 halftone dots with 10 % interference , 320 halftone dots with 20 % interference and 640 halftone dots with 40 % interference . and the results are listed in the following table with units in %. table 4 gives the error rates of the example for comparison . 1100110011001100 and 0011110011001100 , with a similarity value between codes equals to 0 , are repeatedly embedded . at the same time , the detecting error rates are calculated for 160 halftone dots with 10 % interference , 320 halftone dots with 20 % interference and 640 halftone dots with 40 % interference . and the results are listed in the following table with units in %. as shown in the implementations above , when the halftone dots undergo interference , the lower the similarity between codes , the smaller the detecting error rate ; verse vice . it is clearly seen that the detecting error rate is very small when the similarity value is below ½ .