1. An image processing method, comprising: determining an abscissa and an ordinate of a reference control point and a reference slope of a curve passing the reference control point according to an image of different tissue sites and/or different orientations depending upon one or more practical requirements; calculating an average value of pixels in an area of interest in the image and using the average value as a current image feature value; constructing an S-shaped reference tone scale curve equation by using the coordinates of the reference control point and the reference slope; substituting coordinates of a new control point and a slope of a curve passing the new control point into the S-shaped reference tone scale curve equation to calculate parameters therein, so as to obtain the adaptive image tone scale curve; and transforming the image using the image tone scale curve for display on a display device, wherein an abscissa of the new control point is the image feature value multiplied by a coefficient greater than zero, an ordinate of the new control point is the ordinate of the reference control point, and the slope of the curve passing the new control point is the reference slope multiplied by a ratio of the abscissa of the reference control point to the image feature value.