Morphological opening is Morphological Erosion followed by Morphological Dilation with the same kernel width . It is transitively also a nonlinear Filter applied to a Signal.
- The net effect is that any spectral feature narrower than bins is removed; broader features are preserved. Applied to a Power Spectrum, the result is a smooth estimate of the noise floor envelope which is the basis of the Automatic Noise Floor Spectrum Estimation in the Presence of Signals
- This is a Stencil operation: each output depends only on a fixed neighborhood of surrounding inputs, with an erosion then dilation instead of a weighted sum. The order of operations matters.