Watermark

Watermark hides one image inside another, and can extract it again later. Both images must be 8-bit, monochrome or color (1 or 3 bands), and the same size.

Connect the image to input_link and the watermark image to watermark_link, and choose the “watermark type”:

• merged (the default): the watermark is stored in the lowest bits of each pixel. “watermark” sets how many bits it uses (default 2, up to 8); the input image keeps the remaining 8 − N bits. Error diffusion is used on both images to spread out the errors that combining them causes.
• inserted: the watermark is converted to a 1-bit image with error diffusion, and stored in the lowest bit of each pixel. The input image is quantized with error diffusion to make room for it.

The watermark is not visible in the output image. Save the watermarked image as an 8-bit TIFF file.

Read the watermarked image into Watermark's input link by itself, with nothing on the watermark link, and choose the same watermark type. For a merged watermark, the bits in each pixel are reversed in order; for an inserted one, the lowest bit is extracted and output.