Some of the components cannot work without source data. For example, Blur needs a source image to process, Elevation Gradient requires both a gradient and a height map to produce its output image, and the Amplitude curve component needs a source curve to amplify. If a component cannot produce its output without certain source data, the corresponding inputs (called required inputs) are displayed in red on the component's body:
When a required map input is unconnected, the component receives the image of an exclamation mark within a red circle as a substitute for the required data. This way, the component as a whole and all its other parameters and inputs remain functional, and the users can preview the component's output (to a limited extent) without having to supply the required data. When a required curve input is unconnected, the component receives a zero-level 'flatline' curve as a substitute for the required curve.
Having unconnected required inputs in a filter is not a problem per se. However, such filters are not accepted into the Filter Library, they are blocked by the Submit Wizard. To solve this problem, connect components of appropriate types to all required inputs in the filter and resubmit it. Note that required inputs don't accept connections from numeric components.
