Image forming apparatus for weight property determination

An image forming apparatus comprising:

• an optical sensor comprising a light emitter to accommodate a light-emitting element, the light emitter to radiate light to a medium on which a toner image is formed, and a light receiver to detect an amount of transmitted light, an amount of regular reflected light, and an amount of diffuse reflected light;
• and
• a processor to calculate a glossy sheet-thickness coefficient by adding a reflected-light-amount-equivalent value to a transmitted-light-amount-equivalent value, wherein the reflected-light-amount-equivalent value is obtained when the amount of regular reflected light is standardized based on the amount of diffuse reflected light, and wherein the transmitted-light-amount-equivalent value is based on the amount of transmitted light,
• the processor to determine a weight property of the medium based on the glossy sheet-thickness coefficient, wherein the weight property comprises a basis weight or a thickness of the medium.