1. A method of image depth estimation, comprising: calculating a hue value of each pixel in an image by comparing a plurality of color components in a color space of each pixel in the image; associating the hue value of each pixel in the image with a corresponding value, wherein the corresponding value is a first numerical value or a second numerical value; and according to the corresponding value of each pixel in the image, calculating a depth value of each pixel in the image, wherein the depth value is used to convert the image into a three-dimensional (3D) image to be displayed on a 3D display apparatus.