Spatial Domain Watermarking Scheme for Colored Images Based on Log-average Luminance

TL;DR

This paper introduces a novel spatial domain watermarking method for colored images that leverages log-average luminance to embed and extract monochrome watermarks, demonstrating robustness against common image modifications.

Contribution

The paper proposes a new watermarking scheme based on log-average luminance and a spiral block selection method for colored images, enhancing robustness and imperceptibility.

Findings

Effective against grayscale conversion

Resistant to image cropping

Robust under JPEG compression

Abstract

In this paper a new watermarking scheme is presented based on log-average luminance. A colored-image is divided into blocks after converting the RGB colored image to YCbCr color space. A monochrome image of 1024 bytes is used as the watermark. To embed the watermark, 16 blocks of size 8X8 are selected and used to embed the watermark image into the original image. The selected blocks are chosen spirally (beginning form the center of the image) among the blocks that have log-average luminance higher than or equal the log-average luminance of the entire image. Each byte of the monochrome watermark is added by updating a luminance value of a pixel of the image. If the byte of the watermark image represented white color (255) a value <alpha> is added to the image pixel luminance value, if it is black (0) the <alpha> is subtracted from the luminance value. To extract the watermark, the selected blocks are chosen as the above, if the difference between the luminance value of the watermarked image pixel and the original image pixel is greater than 0, the watermark pixel is supposed to be white, otherwise it supposed to be black. Experimental results show that the proposed scheme is efficient against changing the watermarked image to grayscale, image cropping, and JPEG compression.