A High-Capacity Quantum Image Steganography Scheme Based on a Double-Layer Tortoise Shell Matrix

In recent years, quantum image steganography has attracted considerable attention; however, achieving high embedding capacity while preserving imperceptibility and security remains challenging. To address this issue, a quantum color image steganography scheme based on a double-layer turtle shell matrix is proposed.The scheme transforms RGB into the YCbCr color space to separate luminance and chrominance components according to the human visual system (HVS), and embeds secret information mainly into chrominance channels in combination with a check-digit mechanism to reduce visual distortion and enhance security. Meanwhile, the double-layer turtle shell matrix allows each coordinate to store more secret information. By jointly combining the YCbCr-based perceptual embedding strategy with the double-layer turtle shell matrix, the proposed scheme achieves 5 bpp embedding capacity while maintaining a PSNR above 50 dB.Moreover, the Grover search algorithm is incorporated to exploit quantum parallelism, significantly reducing the time complexity of searching embedding coordinates. A corresponding quantum circuit diagram is provided as a fundamental component for realizing the embedding and extraction processes. Experimental comparisons demonstrate that the proposed scheme outperforms existing methods in imperceptibility and embedding capacity, with a particularly notable improvement in payload.