![]() As a bonus, you can make a version that lets the user dynamically set the green threshold (and even updates the resulting image dynamically - for small images!). How high is a high green pixel value? That can differ for different green screens, but 240 is a good general estimate. That does not work in general, but it does in typical color images shot in front of a green screen. Greenness can be difficult to determine, but the easiest way is to assume that pixels with a high green pixel value represent green (regardless of its red and blue values). Of course, if you are too permissive, then you might match parts of the characters outfits making it appear like they are see through!Ī basic version of the algorithm is fairly simple: combine the pixels from two images into one image by using the "greenness" of the foreground image to determine whether or not to use the background image pixel instead in the new image. Green is the easiest color to match but you need to be a little forgiving in the amount of green you require since any real set has shadows or highlights so it is not a uniform shade of green. ![]() It works by compositing a foreground image with a background image by replacing all the "green" pixels in the foreground image with the corresponding pixel from the background image. Implement the green screen (also known as "chromakey") algorithm typically used in movies or news weather broadcasts to make the characters appear to be in a different location than they really are. This means you will not need to edit the HTML or CSS files, but you will need to understand their contents to attach your JavaScript code to the events that can be generated. ![]() Exercise: JavaScript Green Screen Image Filterįor this exercise, instead of focusing on the document's structure and style (HTML and CSS), use JavaScript to computationally change images that are uploaded to the page.
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