Why is watermark embedded in only luminance components rather then in chroma components as well in image/video?
[Neil F. Johnson] It has more to do with the survivability of the marked areas within an image. Color can easily be changed or converted to grayscale and you still have a “useable” image. In marking an image, one want to place the mark in the more robust areas of an image. Areas of high luminance is not the correct assessment, because a plain sky may have high luminance but a poor structure for hiding information. What the watermark tools are really interested in are areas with high gradient magnitude. In other words, relatively strong edges with respect to the structure of the image and the luminance variances of the “edges.” [Lars R. Randleff] A lot of watermarking schemes hide data in the luminance/intensity due to the fact that the Human Visual System (HVS) use most of its bandwidth on percepting (changes in) brightness. In changing an image, by e.g.
[Neil F. Johnson] It has more to do with the survivability of the marked areas within an image. Color can easily be changed or converted to grayscale and you still have a “useable” image. In marking an image, one want to place the mark in the more robust areas of an image. Areas of high luminance is not the correct assessment, because a plain sky may have high luminance but a poor structure for hiding information. What the watermark tools are really interested in are areas with high gradient magnitude. In other words, relatively strong edges with respect to the structure of the image and the luminance variances of the “edges.” [Lars R. Randleff] A lot of watermarking schemes hide data in the luminance/intensity due to the fact that the Human Visual System (HVS) use most of its bandwidth on percepting (changes in) brightness. In changing an image, by e.g. JPEG compression, one therefore has to be more gentle to the brightnes information than to the color information (hue/saturation) sin
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