A signal processing method of a transparent display is disclosed. The signal processing method includes: receiving an input signal; performing a signal conversion step on the input signal to form a converted signal; after performing the signal conversion step, performing a signal identification step based on the converted signal; generating an image signal and a control signal from the input signal and a signal identification result of the signal identification step; outputting the image signal for light emission adjustment of the transparent display; and outputting the control signal for transparency adjustment of the transparent display, wherein a converted gray scale of a pixel is obtained by multiplying at least two gray scales among a red gray scale, a green gray scale, and a blue gray scale of the pixel by previously set corresponding coefficients and summing the multiplied gray scales.