pu221e

Puzzle. Hide secrets into a picture.

How it works

Each picture has pixels. Each pixel has red, green, blue colors. Each color is a number in computer.

For example, a pixel #f0c7bde:

| Color | Decimal | Binary | | ----- | ------- | ------ | | Red | 12 | 00001100 | | Green | 123 | 01111011 | | Blue | 222 | 11011110 |

I can use low digit of a color to storage message. First, I need to clean low digit. For example, clean low 4 digits of the binary of the color:

| Color | Binary | | ----- | ------ | | Red | 00000000 | | Green | 01110000 | | Blue | 11010000 |

Every character of a message is a number in computer. For example:

| Character | Binary | | --------- | ------ | | a | 01100001 |

Pick high 4 digits and write it into low 4 digits of red color. Pick low 4 digits and write it into low 4 digits of green color. It will become #0671d0；

| Color | Binary | Decimal | | ----- | ------ | ------- | | Red | 00000110 | 6 | | Green | 01110001 | 113 | | Blue | 11010000 | 208 |

The difference between the two colors is small:

• #f0c7bde
• #0671d0

If there is more then 1 character, I can also use blue color of pixels.

When I want to decode message from the pixel. I can just pick low 4 digits of each color, and splice them as a string.

How to use

Install

npm install pu221e -g

Encode message into picture

pu221e e ./pure_img.png ./img_with_message.png 'This is a secret message.'

Decode message from picture

pu221e d ./img_with_message.png

Knowing issues

Does not support outputting jpg format

Because of issue of jimp. It support use jpg format as input, but does not support outputting jpg format.