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  1. I have an image that is a map (snippet below). I'd like to use this in Google Sheets, but they don't allow background images. So I have a plan to convert the map, but I need some help. The idea is to use edge detection to strengthen all the edges to black, then somehow select all the other regions and delete them, converting them to transparency. I'm having two issues: 1. How do I make the lines strong enough between zones? (Outline seemed to work, but Edge Detection destroyed that strength.) 2. How do I select all areas under a certain luminance threshold, in ord
  2. With the help of MJW's advice, I came up with an amazingly good result, which I thought I'd share. What I realised was that the noise (animated snow) is almost entirely different on each image. That is, snow particles rarely overlap between images. So taking the difference between two otherwise identical images results in just the snow particles on a black background. I reasoned that this could be subtracted back from the combination of the two original images, factoring in the fact that each contributes half of the intensity. So, if the two background images are BG1 an
  3. Thanks, MJW. I actually had a feeling about the opacity. I haven't worked much with image manipulation (my expertise is more in compression). Thanks for pointing out that setting 50% opacity is the same as averaging. I think that will give a perfectly adequate result, even if there are better theoretical options. I might experiment with the 33% suggestion, but as you point out, it can effectively be replicated with three 50% blends, near enough. My only other option was to write some Matlab code, and I'm not even sure if my Matlab licence is stil
  4. Hi all, I'm trying to remove known backgrounds from some images, which is easy enough in itself -- except some of the images and backgrounds are overlaid with random "noise." I'm wondering what's a good way to get a "good enough" result. The basic setup is that I have two images (screenshots from a game). The first image is the background. The second image is the background plus an overlay image. I'm after the overlay image. So I insert the second image as a layer over the top of the first image and set the new layer's blend mode to "Difference". Flatten and voila! Work
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