A robust blind watermarking scheme for color digital images based on GJO and the maximal connected domain

The problem of image piracy is becoming more and more severe in today’s society contemporary society. To resolve this problem of protecting the copyright of color images, a robust color image blind watermarking scheme based on the golden jackal optimization algorithm (GJO) and the maximal connected domain is proposed. GJO is adopted to select the threshold of the maximal connected domain and the quantization step of watermark embedding, and the maximal connected domain of the main image is selected as the embedding region based on a specific threshold. Then, the embedding area is divided into RGB three-layer channels. Each layer of channels is divided into non-overlapping matrix blocks with size of 4×4. Two watermark bits are embedded in each block. Specifically, two watermark bits are quantized and embedded into the first two elements in the first row of the matrix after the Householder transform, and double overflow treatment is applied to the embedded values of the watermark to improve its robustness. The experimental performances are shown as follows: 1) the average values of PSNR and SSIM are above 40 dB and 0.96, respectively; 2) the values of NC are above 0.95 under different attacks; 3) the theoretical maximum capacity for watermark information is four times the actual capacity; 4) The time complexity of embedding a watermark bit is O(n²). The experimental results indicate that the scheme proposed exhibits good performance in robustness, invisibility, time complexity, watermark embedding capacity, and other aspects.