1. An artifact reduction method, comprising: scaling down a resolution of each of at least one previous original image frame from a first resolution to a second resolution to obtain at least one previous low-resolution image frame and storing the at least one previous low-resolution image frame in a buffer unit; scaling down a resolution of a current original image frame from the first resolution to the second resolution to obtain a current low-resolution image frame, wherein the current original image frame and the current low-resolution image frame comprise a first plurality of pixels and a second plurality of pixels, respectively; performing an artifact detection to the current low-resolution image frame to obtain a plurality of low-resolution weights in accordance with a relation of the current low-resolution image frame and the at least one previous low-resolution image frame retrieved from the buffer unit, wherein the low-resolution weights are respectively corresponding to the second plurality of pixels in the current low-resolution image frame, and the step of performing the artifact detection to the current low-resolution image frame to obtain the low-resolution weights comprises: for each pixel in the second plurality of pixels of the current low-resolution image frame, respectively executing following steps: (i) comparing a color or brightness value of a pixel in the current low-resolution image frame with a color or brightness value of the pixel in the at least one previous low-resolution image frame; and (ii) if the comparison result satisfies a predetermined condition, adjusting a color or brightness weight corresponding to the pixel in the low-resolution weights of the at least one previous low-resolution image frame to generate the color or brightness weight corresponding to the pixel in the low-resolution weights of the current low-resolution image frame; scaling up a number of the low-resolution weights to generate a plurality of high-resolution weights, wherein the high-resolution weights are respectively corresponding to the first plurality of pixels in the current original image frame; and performing a temporal noise reduction to the current original image frame by using the high-resolution weights for reducing artifact of the current original image frame and obtaining an adjusted image frame, wherein the step of performing the temporal noise reduction to the current original image frame comprises: for each pixel in the first plurality of pixels of the current original image frame, respectively executing following steps: calculating a color or brightness value of a pixel in an adjusted image frame based on a color or brightness value of the pixel in the current original image frame, a color or brightness value of the pixel in a previous adjusted image frame, and a color or brightness weight corresponding to the pixel in the high-resolution weights.