Image forming apparatus and a developing apparatus having a unit for determining a mixture ratio of two types of magnetic toner based on magnetic permeability and amount

摘要

An electrophotographic image forming apparatus includes a developer reservoir for accommodating a single-component mixed developer including two types of toner having a generally identical hue and different reflection densities. A magnetic substance is added to one of the two types of toner. The apparatus also includes a detector for detecting a magnetic permeability of the developer in the developer reservoir and a unit for determining a mixture ratio of the two types of toner based on the magnetic permeability of the developer detected by the detector.