The dynamic range of illumination in the real world which can reach up to 14 orders of magnitude from star light to sun light. The human eye can see a wide dynamic range of up to 5 orders of magnitude. However, most display devices can only display images with a dynamic range of around 2 orders of magnitude. Liquid crystal display panels for example can typically only display images having an 8-bit (256 step) luminance dynamic range. Therefore, a luminance mapping transfer is used to map from the dynamic range of the real world to the lower dynamic range of the display. This results in a lose of contrast and detail of the image. Generally this mapping is performed in the image capture stage since some digital cameras is able to capture images with 12 to 16 bits luminance dynamic range. Conversion from a greater to a lower luminance dynamic range for the display is referred to as Tone Mapping.
Recent developments in display technology have resulted in displays that can show images with a high luminance dynamic range. However, as many images are converted to a lower 8-bit luminance dynamic range n capture, and many conventional video has an 8-bit luminance dynamic range, there is a need for a reverse process of increasing the luminance dynamic range of a digital image for use with these high dynamic range displays. The most straight forward way to enlarge the dynamic range is simply multiple a constant to each pixel value. However, such linear stretch does not consider the image characteristic and human visual system property. As a result, it can not improve the image quality. Moreover, the linear scaling up approach may cause artifacts, such as introducing countering effect into gradually changing regions.
Accordingly, it is an object of the present invention to provide a method of displaying a low luminance dynamic range image in a higher luminance dynamic range.