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If the same watermark is added to each image, then you can estimate the watermark by averaging many images and subtract it to get original image back. If each
by pps43 9y ago
If the same watermark is added to each image, then you can estimate the watermark by averaging many images and subtract it to get original image back.
If each image has a slightly different watermark, then simple averaging won't work. Instead you need to come up with a model that describes how the watermark is changing, then estimate parameters of that model. The more complex the change, the more images you need for parameter estimation.
Image stabilization won't work here because it relies on large features and therefore won't be sensitive to relatively weak watermark signal. Besides, it's only stabilizing in three dimensions (pitch, roll, yaw) and won't help with warping within the image.
- Retric 9y agoAveraging will still provide the average watermark given a large enough sample set. Which is then a single geometric transformation from the used watermark. Estimating that transformation for a specific image should be fairly straightforward as they could easily reverse a watermark that was offset. At which point it's reversible.
- pps43 9y agoNot really, because in each image parts of the watermark will be in different places. You don't even need to warp the watermark to achieve that, it's enough to randomly reposition it.
- Retric 9y agoSupose you have 4 points on a box. If you randomly increase or decrease the location of each point by some random value say +-3% then averaged 100,000 of those boxes, you get a smaller box(1) surrounded by a larger increasingly blurry box. This is true even if no single picture shows that single smaller box, but it will show up on the average. (1) Rather than a true box the midpoints are going to be slightly buldging, but with a large sample set it's very close to a box. Sure, you can get into cat and mouse games ever stranger geometry. But, the water mark is limited by how much it distracts from the image.
- pps43 9y agoThe article shows the result of this approach, and it clearly does not work well.
- Retric 9y agoAs I said you need a new step: "Estimating that transformation for a specific image should be fairly straightforward". It does show a good average and simply moving the watermark was easily reversible suggesting detection of a watermark in an image was easy.
- Dylan16807 9y agoIt has crisp edges. If the same watermark is repositioned it's trivial to figure out the adjustment and remove it. Warping is harder but still largely doable by finding each part of the watermark's exact location.