1. A method for measuring a response curve of an image sensor, comprising: taking a single photograph of a Grey Scale card with an image sensor to be measured, wherein said Grey Scale card is a reflective Grey Scale card or a transmissive Grey Scale card, said Grey Scale card has a plurality of greyscale blocks, each grayscale block having a uniform greyscale, different greyscale blocks having different greyscales, a reflectivity or a transitivity of each greyscale block on said Grey Scale card is marked, and said single photograph comprises a plurality of greyscale image blocks respectively corresponding to said greyscale blocks; calculating a relative exposure value for each greyscale image block of said single photograph, wherein said relative exposure value is a product of an exposure time with which a corresponding photograph is taken and said greyscale of corresponding greyscale block, said greyscale of a greyscale block is represented by its reflectivity or transitivity; plotting a plurality of reference points based on pixel values of pixel points within each greyscale image block and said relative exposure values of said greyscale image blocks, wherein said reference points have said pixel values as an ordinate and said relative exposure values as an abscissa; and executing an interpolation calculation based on said plurality of reference points to obtain a response curve of said image sensor.