Bit-Plane Inspector

What it's for

See each bit of an image’s colour channels on its own, pull out the data stored in the lowest bits, and compare two images pixel by pixel. Hidden messages and watermarks that are invisible in the picture often show up clearly in a single bit plane. Tools like this are a staple of capture-the-flag challenges.

For example, when a challenge gives you a PNG that “looks normal”, step through its bit planes for a hidden picture, then extract the low bits to look for text.

How to use it

Choose an image, or drop one on the Image box. Use the list or the arrows to step through the full image and each bit of red, green, blue and alpha, from bit 7 (the most significant) to bit 0; set bits show white. Choose a second image under Compare with and pick Differences from the second image to see which pixels differ.

Extract reads the chosen bit of the channels you list (such as RGB or BGR), pixel by pixel along rows or down columns, into bytes. The first 256 bytes are shown in hex and as text; Download .bin saves them all. These settings are remembered.

Example

Hide a message with the Image Steganography tool and save the PNG. Choose that PNG here, keep RGB, bit 0, row by row and most significant bit first, and choose Extract. The text starts:

TBX1

which is the Image Steganography tool’s marker, followed by the message.

Good to know

PNGs are read exactly, bit for bit. Other images, and the rare PNGs this can’t read itself (16-bit or interlaced), are decoded by the browser, so their lowest bits may differ slightly, and some privacy settings add noise to them. Only images the browser can open are supported.