When editing images it is often desirable to apply a filter with a spatially varying strength. With the usual
selection tools like gradient, lasso, brush, or quick selection tools, creating masks containing such spatially
varying strength values is time-consuming and cumbersome. We present an interactive filtering approach which
allows to process photos selectively without the intermediate step of creating a mask containing strength values.
In using this approach, the user only needs to place reference points (called control points) on the image and to
adjust the spatial influence and filter strength for each control point. The filter is then applied selectively to the
image, with strength values interpolated for each pixel between control points. The interpolation is based on a
mixture of distances in space, luminance, and color; it is therefore a low-level operation.
Since the main goal of the approach is to make selective image editing intuitive, easy, and playful, emphasis
is put on the user interface: We describe the process of developing an existing mouse-driven user interface into
a touch-driven one. Many question needed to be answered anew, such as how to present a slider widget on a
touchscreen. Several variants are discussed and compared.