Fast bit extension device and method

The present invention proposes a fast bit extension device and method, wherein the limitation that each channel of analog/digital converter can only handle 8 bit data can be resolved by providing additional bits during the postprocessing of image, so that the processing of the image bit depth is more accurate. The bit extension device of the present invention receives two of the least important bits outputted from the back pixel memory device and the front pixel memory device for computation, and adds the compensation bits on the end of the byte of the pixel being processed, and accomplish the purpose of increasing the number of bits, so that the color tone processing is more accurate. Furthermore, since the expanded bytes keep the bytes in the original pixel, the data in the original pixel can be preserved completely, so that the image won't be blurred due to the extended bits.