1. A method to modify a digital image including a plurality of pixels, the method comprising: receiving selection of a first image reference point, the first image reference point associated with a first mixing function; receiving selection of a second image reference point, the second image reference point associated with a second mixing function; for at least one pixel of the plurality of pixels, determining a first effect strength for application of the first mixing function based on a first similarity between the at least one pixel and the first image reference point; for the at least one pixel of the plurality of pixels, determining a second effect strength for application of the second mixing function based on a second similarity between the at least one pixel and the second image reference point; and updating the at least one pixel by application of the first mixing function based on the first effect strength and by application of the second mixing function based on the second effect strength.