The ready availability of camera technology, particularly in small, lightweight computing devices, has increased the prevalence of amateur photography. Hardware and imaging software in both computing devices and dedicated digital cameras have advanced so that photographers of all levels have access to highly advanced image processing that can be applied to images in many ways and at any time, even immediately after image capture on a device. One area in which image processing still sometimes falls short is when image processing is applied to images taken at or near the limits of the dynamic range of the imaging sensor being used. Such images might be taken, as an example, during exposure bracketing for high dynamic range (“HDR”) photography or for image selection.
In order to adjust the exposure of such images during further processing, existing applications typically refer to exchangeable image file (“EXIF”) data within the image files. EXIF data values are typically assigned based on camera settings assuming that the luminance response of a digital image sensor is linear, or nearly so. In practice however, most digital image sensors become nonlinear near their limits. For example, most digital image sensors are nonlinear in their response to light at levels that are very low relative to the sensor's native sensitivity. Thus, it is difficult to achieve optimum results when using the “dark” image of a series of images captured of a scene for image enhancement, for example, to form a combined image through HDR photography.