1. A method for reducing digital image noises, applied in an electronic computing device, to process image noises of a plurality of pixels in a digital image, the method comprising: sequentially selecting one of the pixel from the pixels of the digital image, and setting the pixel as a target pixel; defining a first area, wherein the target pixel is located at a center of the first area, and setting at least two of the rest pixels surrounding the target pixel in the first area as a plurality of adjacent pixels; setting a first weighted area, wherein the target pixel is located at a center of the first weighted area; setting a second weighted area, wherein one of the adjacent pixels is located at a center of the second weighted area, and the second weighted area is corresponding to the first weighted area; computing a weight of the adjacent pixel at the center of the second weighted area by using a piecewise linear curve according to a similarity value of the first weighted area and the second weighted area; computing a weighted average of all the adjacent pixels and the target pixel, and determining a new value of the target pixel according to the weighted average; and performing the above steps repeatedly, till all the pixels in the digital image are processed.