1. A text image trimming method comprising: obtaining text image data of a text image; using a straight line detection method to detect straight lines in the text image; identifying and storing on a memory a set of trimmed quadrangles based on the detected straight lines, and obtaining edges of each of the trimmed quadrangles; detecting text in the image data, identifying a text region based on the detected text, and obtaining coordinates of boundary points of the text region; and obtaining a final trimming result according to the obtained edges and coordinates, wherein obtaining the final trimming result comprises: forming a set of candidate quadrangles composed of all obtained trimmed quadrangles; if the set of candidate quadrangles is empty, asking a user for manually determining a trimmed quadrangle and ending the method; if the set of candidate quadrangles is not empty, selecting a candidate quadrangle from the set of candidate quadrangles, and then determining if all the edge points of the text region are in the selected candidate quadrangle, thereafter: if all the edge points of the text region are in the selected candidate quadrangle, setting the candidate quadrangle as a valid trimmed quadrangle, outputting the valid trimmed quadrangle and the ending the method; or if all the edge points of the text region are not in the selected candidate quadrangle, selecting a subsequent candidate quadrangle from the set of candidate quadrangles, and then determining if all the edge points of the text region are in the subsequently selected candidate quadrangle.