2. An overlapped handwriting input method, comprising: Step S 111 : touch a touch screen with a handwriting pen or finger to, and starting to input a stroke; Step S 112 : moving the handwriting pen or finger on the touch screen, recording and displaying the track of the stroke on a handwriting area of the touch screen, and drawing the track of the current stroke by using a given color A; Step S 113 : moving the handwriting pen or finger away from the touch screen, and ending the input of the current stroke; Step S 114 : determining whether the stroke being currently written and all previously input strokes having the color A belong to the same character; if yes, going to Step S 124 ; otherwise, going to Step S 115 ; Step S 115 : determining whether an inactive visual layer character is present on the screen, wherein the inactive visual layer character refers to the last completely written character that has undergone recognition and color transformation, and the character is defined in Step S 117 ; if yes, going to Step S 116 ; otherwise, going to Step S 117 ; Step S 116 : clearing an image of the inactive visual layer character and related stroke information; Step S 117 : defining a character constituted by all strokes having the color value A, except for the current stroke, as the inactive visual layer character; Step S 118 : submitting data of the current inactive visual layer character to a recognition engine for recognition, and outputting recognition result; Step S 119 : determining whether the recognition result provided by the recognition engine is reliable enough; if yes, going to Step S 120 ; otherwise, going to Step S 122 ; Step S 120 : fading the color of the strokes of the current inactive visual layer character until disappearance of the color; Step S 121 : clearing the image of the inactive visual layer character and the related stroke information; going to Step S 123 ; Step S 122 : transforming the color of the strokes of the current inactive visual layer character to another color B for display; Step S 123 : determining whether a new stroke is input, and if yes, going to Step S 112 ; otherwise, going to Step S 126 ; Step S 124 : keeping the color of the current stroke unchanged; Step S 125 : determining whether a new stroke is input, and if yes, going to Step S 112 ; otherwise, going to Step S 126 ; Step S 126 : submitting the data of the character being currently written to the recognition engine for recognition, and outputting a recognition result; and Step S 127 : Ending.
2. An overlapped handwriting input method, comprising: Step S 111 : touch a touch screen with a handwriting pen or finger to, and starting to input a stroke; Step S 112 : moving the handwriting pen or finger on the touch screen, recording and displaying the track of the stroke on a handwriting area of the touch screen, and drawing the track of the current stroke by using a given color A; Step S 113 : moving the handwriting pen or finger away from the touch screen, and ending the input of the current stroke; Step S 114 : determining whether the stroke being currently written and all previously input strokes having the color A belong to the same character; if yes, going to Step S 124 ; otherwise, going to Step S 115 ; Step S 115 : determining whether an inactive visual layer character is present on the screen, wherein the inactive visual layer character refers to the last completely written character that has undergone recognition and color transformation, and the character is defined in Step S 117 ; if yes, going to Step S 116 ; otherwise, going to Step S 117 ; Step S 116 : clearing an image of the inactive visual layer character and related stroke information; Step S 117 : defining a character constituted by all strokes having the color value A, except for the current stroke, as the inactive visual layer character; Step S 118 : submitting data of the current inactive visual layer character to a recognition engine for recognition, and outputting recognition result; Step S 119 : determining whether the recognition result provided by the recognition engine is reliable enough; if yes, going to Step S 120 ; otherwise, going to Step S 122 ; Step S 120 : fading the color of the strokes of the current inactive visual layer character until disappearance of the color; Step S 121 : clearing the image of the inactive visual layer character and the related stroke information; going to Step S 123 ; Step S 122 : transforming the color of the strokes of the current inactive visual layer character to another color B for display; Step S 123 : determining whether a new stroke is input, and if yes, going to Step S 112 ; otherwise, going to Step S 126 ; Step S 124 : keeping the color of the current stroke unchanged; Step S 125 : determining whether a new stroke is input, and if yes, going to Step S 112 ; otherwise, going to Step S 126 ; Step S 126 : submitting the data of the character being currently written to the recognition engine for recognition, and outputting a recognition result; and Step S 127 : Ending. 6. The overlapped handwriting input method according to claim 2 , wherein: in Step S 119 , the method for determining the recognition reliability of the recognition engine recognizing a certain handwritten character comprises: calculating the difference between a probability of the character to be recognized belonging to a first candidate character and a probability of the character to be recognized belonging to a second candidate character, and if the difference is greater than a certain threshold, determining that the reliability of the recognition result provided by the recognition engine is high; the method of calculating the probability of the character to be recognized belonging to a certain candidate recognition result character is provided by a recognition classifier; a quadratic discriminant function classifier is used as the classifier, and the probability is approximate to a negative exponent of a recognition distance provided by the quadratic discriminant function classifier.