1. A method for adjusting image characteristics, said method comprising: a. receiving an input image; b. receiving ambient illumination data; c. determining a reduced source light illumination level for an image display device source light, said reduced source light illumination level being based on said ambient illumination data, wherein said reduced source light illumination level is less than a full brightness level; d. calculating a tone scale adjustment model based on said reduced source light illumination level; wherein said tone scale adjustment model fully compensates said input image for said reduced source light illumination level only for input image code values below a maximum fidelity point and partially compensates for said reduced source light illumination level with a roll-off curve only for input image code values above said maximum fidelity point and wherein said calculating is performed by a processor and a memory; and e. applying said tone scale adjustment model to said input image.