duotone filter base icon png download

Evolution of a simple duotone filter. First square is unfiltered, second one is filtered to greyscale colours, third one has a colormatrix set "luminance to alpha", 4th one is superimposed on a white fill, resulting in an inverted greyscale appearance, 5th one has another luminance to alpha set, that is what it was all about. As a result, the 6th one is using 2 flood fills and compositing, making up a duotone shading. The last one has a component transfer filter primitive added, which you can use for fine tuning the look if you apply the filter on a photograph.