DIGITAL WATERMARKING OF COLOR IMAGES USING AMPLITUDE-MODULATION

Digital watermarking techniques sign images by introducing changes tha t are imperceptible to the human eye but easily recoverable by a compu ter program. Generally, the watermark is a number which identifies the owner of the image. The locations in the image where the watermark is embedded are determined by a secret key. Doing so prevents possible p irates from easily removing the digital watermark. Furthermore, it sho uld be possible to recover the embedded watermark from an altered imag e. Possible alterations of signed images include blurring, compression , and geometrical transformations such as rotation and translation. Th ese alterations are referred to as attacks. A new method based on ampl itude modulation is presented. Single watermark bits are multiply embe dded by modifying pixel values in the blue channel These modifications are proportional to the luminance and either additive or subtractive, depending on the value of the bit This new method has shown to be res istant to both classical attacks, such as filtering, and geometrical a ttacks. Moreover, the watermark can be recovered without the original image. (C) 1998 SPIE and IS&T. [S1017-9909(98)00102-0].