Blend - Extrapolation

Extrapolation - allowing an "opacity" of less than 0% or more than 100% - would be a powerful extension to the Blend component. When used to blend between the original and processed version of an image, it becomes a processing tool in its own right.

For example, a negative blend ("opacity") between the original and a blurred version produces a form of sharpening.

Between the original and a monochrome version it becomes a saturation control, 100%+ turning UP the saturation.

Below 0% when blending between the original and a flat colour introduces a colour cast.

i dont quite follow how you can have an opacity of less than 0% or more than 100%. 0% opaque is simply fully transparent and 100% opaque is simply fully solid. so, i'm a bit lost here how you make that jump in logic and function.

craig

Craig, you're thinking too physically about the numbers - they're only numbers, not limits.

If you define a blend, where the control 'c' selects between the two inputs 'a' and 'b', one would represent this as

new = a + c * (b - a)

where 'c' varies between 0 to get 'a' and 1 to get 'b' - in your terminology these would be 0% and 100%. However, you still get a result when you use some other value for 'c' - if you used 2, or 200%, the result is new = 2b - a, if you used -1 you'd get new = 2a - b. etc.

Think of it this way, if your two inputs are a colour image, and a greyscale version, then values between 0 and 100% give you various amounts of saturation, values above 100% increase the saturation (possibly to the point of clipping, of course), and values below 0 invert the colours and saturate.