therefore the present invention can transmit secret message securely and realize covert communication application_number US 201113033384 A description the present invention proposes a method for embedding a secret message into a png portable network graphics image which realizes high security covert communication via hiding a secret message into a png image and transmitting the secret message together with the png image neither distorting the content of the png image nor changing the rgb channels of the png image below the embodiments are described in detail to demonstrate the technical contents of the present invention refer to fig1 an exploded view schematically showing the format of a png image according to one embodiment of the present invention a png image 10 has four channels an r red channel 12 a g green channel 14 a b blue channel 16 and a transparency alpha a channel 18 the color channels r red channel 12 g green channel 14 and b blue channel 16 respectively contain corresponding color values the color value ranges from 0 to 255 of the decimal system the transparency of the alpha channel 18 is also expressed by 0 255 of the decimal system wherein 0 denotes u201c white u201d or u201c opaque u201d and 255 denotes u201c full transparent u201d below is described in detail the process of embedding a secret message into a png image refer to fig2 a flowchart of.