In daily life, we often see the existence of digital image watermarks. For example, as shown in Figure 1. Digital image watermarking also plays a very important role in daily life. They protect the rights of owners in various ways, including:
Copyright identification;
Copyright recognition;
Copy protection.
Figure 1 Digital image watermark
The watermark superposition formula of digital image is:
-------------------------------(1)
As shown in formula 1, the unwatermarked image is expressed as f and the watermark is expressed as w, and the constant a controls the relative visibility of the watermark and the substrate image. If a is 1, the watermark is opaque and the underlay image is completely dark; as a approaches 0, more underlay images and fewer watermarks will gradually be seen. Usually a is between 0 and 1. As shown in Figure 2, a is a digital watermark, a=0.3 in the b image, and the difference between the watermarked b and the original f in the c image.
Figure 2 A simple visible watermark
2 FPGA implementation of digital image watermarking
Figure 3 FPGA implementation flow chart of digital image watermarking of video images
We want to display a five-pointed star watermark on the terminal of the video image acquisition system:
1) Making of watermark
As shown in Figure 4, we use the drawing tool to make a pattern.
Figure 4 Red five-pointed star watermark
2) The generation of rom file
As shown in Figure 5, we use the BMP2MIF tool to generate .mif files.
Figure 5 BMP2MIF tool
3) FPGA watermark source code:
4) The realization of image watermarking
We took two effects, a =1 and a = 0.5, respectively.
Figure 6 Image without watermark
Figure 7 Watermarked image (a = 0.5)
Figure 8 Watermarked image (a = 1)
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