1. An iterative image testing system based on a two-stage local binary pattern (2SLBP) for super-resolution imaging, the system comprising: an interpolation device that receives a low-resolution input image and accordingly generates an interpolated pixel within a patch of the input image; a clustering device performing the following steps: generating a plurality of gradient direction values according to a center sub-block and neighbor sub-blocks of the patch; quantizing the gradient direction values, thereby generating a quantized gradient direction value; generating a gradient magnitude value according to the gradient direction values; quantizing the gradient magnitude value, thereby generating a quantized gradient magnitude value; and concatenating the quantized gradient direction value and the quantized gradient magnitude value to generate a two-stage local binary pattern (2SLBP) value as an index; a mapping device that stores a plurality of function tables, each including plural mapping functions, one of which is retrieved according to the index; and a prediction device that maps the interpolated pixel to an enhanced pixel according to the retrieved mapping function, thereby generating a high-resolution output image.