Concretely, each bitmap in the stack receives the same filter so the icon stays visually consistent at every size it will be displayed at. You pick the effect and its strength and the transform is applied to the whole file at once.
Which effects are available?
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Grayscale, sepia, invert, blur, sharpen, and brightness, contrast and saturation adjustment. They can be combined, and combining them in one pass is better than running the tool repeatedly.
Does the source format change how a filter looks?
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It can. ICO is a container that holds several square bitmaps at once (16, 32, 48, 64, 128 and 256 px) so Windows and browsers can pick the size they need. Colour depth and the palette model in particular decide how smoothly a gradient or a blur can be represented.
Anything specific to ICO to keep in mind?
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Yes — an ICO is a stack of square bitmaps, not one image, so operations apply to the stack and Windows still picks whichever size it wants. That is often the difference between an effect looking clean and looking banded.
Can I undo a filter after downloading?
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No — the effect is baked into the output pixels, which is the point of applying it. Keep the original file; that is your undo. Grayscale and blur in particular discard information that genuinely cannot be recovered.
Can I apply the same look to a whole set?
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Yes. One filter configuration is applied across the batch, which is how you get a visually consistent gallery rather than a set of individually-tweaked images that almost match.
