The major intention of this work is to introduce a novel hybrid image watermarking technique for RGB color images. This hybrid watermarking algorithm uses two transforms such as Contourlet and Gould transform. The Contourlet transform is used as first stage while the Gould transform is used as second stage. In the watermark embedding phase, the R, G and B channels are transformed using Contourlet transform. The bandpass directional sub band coefficients of Contourlet transformed image are then divided into

Image watermarking [

Watermarking can be performed on spatial domain [

Many researchers are working on image watermarking algorithm [

Initially, the Contourlet transform [

The multiscale decomposition can be achieved by using Laplacian Pyramid (LP). At each level of Laplacian Pyramid decomposition, a low pass of the original image is generated. In multidirectional filter bank the down sampling the signal

In 2006, Le

Therefore, the 2D Gould transform for a 2D gray scale image

Let f_ij be the pixel in a 2 × 2 subimage in ith row and jth column. In a 2 × 2 subimage the discrete Gould transform coefficients specifies the differencing between the neighbouring pixels. The inverse discrete Gould transform for the transformed image F can be obtained using the relation,

From

After embedding the watermark bit

Here,

Input: RGB host image

Output: Watermarked image

Step 1: Separate the channels from the host image

Step 2: Obtain the Contourlet transform for the R channel

Step 3: Subdivided the bandpass directional subband Contourlet coefficients

Step 4: Obtain the Gould transform for the

Step 5: Embed the watermark data

Step 6: Obtain the inverse Gould transform for

Step 7: Merge the

Step 8: Obtain the inverse Contourlet transform for

Step 9: Repeat Step 2 to 8 for G and B channels to obtain

From the Gould coefficients

The algorithm for watermark embedding is given below,

Input: Watermarked image

Output: Extracted watermark

Step 1: Separate individual channels from the watermarked image

Step 2: Obtain the Contourlet transform for the R channel

Step 3: Subdivided the bandpass directional sub-band Contourlet coefficients to

Step 4: Obtain the Gould transform for the

Step 5: Extract the watermark data

Step 6: Repeat 2^{nd} step through 5^{th} step 5 to extract complete watermark data

MATLAB was used to implement the proposed technique with the four test RGB host images shown in

The embedding rate can be calculated as,

Index | Attacks | Specification |
---|---|---|

a | Salt and pepper noise | Noise density 0.05 |

b | Rotation | |

c | Median filtering | Mask size |

d | Cropping | 50% cropping |

e | Brightening | Intensity increase by 60 |

f | Darkening | Intensity decrease by 60 |

g | Gaussian low pass filtering | Filter size |

h | Scaling | Scale by a factor 1.5 |

Watermark | Metrics | RGB Host image | |||
---|---|---|---|---|---|

Airplane | Barbara | Lena | Tiffany | ||

PSNR | 45.31 | 45.29 | 45.315 | 45.257 | |

SSIM | 0.9954 | 0.9966 | 0.9961 | 0.9951 | |

NCC | 0.9999 | 0.9999 | 1 | 0.9913 | |

Apple | PSNR | 45.80 | 45.76 | 45.80 | 45.75 |

SSIM | 0.9951 | 0.9964 | 0.9959 | 0.9949 | |

NCC | 1 | 1 | 0.99999 | 0.99516 |

Attack | Proposed | Improved |
Tensor | LU |
---|---|---|---|---|

Salt and pepper noise | 0.8853 | 0.8621 | 0.8522 | 0.8743 |

Rotation | 0.8447 | 0.8742 | 0.8112 | 0.8331 |

Median filtering | 0.9062 | 0.8891 | 0.8943 | 0.8962 |

Cropping | 0.8709 | 0.8532 | 0.8542 | 0.8675 |

Brightening | 0.7932 | 0.7821 | 0.8641 | 0.8043 |

Darkening | 0.9873 | 0.9568 | 0.9682 | 0.9342 |

Gaussian low pass filtering | 0.9623 | 0.9531 | 0.9523 | 0.9138 |

Scaling | 0.9850 | 0.9631 | 0.9482 | 0.943 |

This paper introduced a novel hybrid color image watermarking algorithm which uses Contourlet transform and Gould transform. The color image is initially transformed using Contourlet transform and the bandpass directional sub-band coefficients are again transformed using Gould transform. The secret data is induced on the

The author with a deep sense of gratitude would thank the supervisor for his guidance and constant support rendered during this research.