Abstract
The work presented here details the development and integration of a consumer-oriented imaging pipeline for the creation, modification, and export of high dynamic range (HDR) image content from RAW standard dynamic range (SDR) images. By increasing dynamic range, the various levels of illumination within a scene can be rendered more accurately, particularly in image highlights, where a higher dynamic range allows details and colors to appear brighter without over-saturation. These changes are designed with the end goal of producing more aesthetically pleasing and true-to-life images. The proposed pipeline utilizes existing image processing techniques found in DxO PhotoLab, a photo editing software package developed by DxO Labs, a private image research company located near Paris, France. Eventually, the developments presented here may be incorporated into a release of PhotoLab. For these reasons, some specific details, such as numerical values in formulas, are obscured due to privacy concerns.
The major developments of this work include the introduction of a new user-controlled HDR up-mapping tone curve that seamlessly integrates with the proprietary PhotoLab tone curve while allowing user control of HDR peak brightness and highlight ramp intensity. The peak brightness control is seemingly a feature unique to this HDR pipeline, whereas the ramp control is analogous to an HDR version of the "Whites" slider present in typical photo-editing softwares. A method to automatically set these parameters to optimal values based on image statics is also presented. Furthermore, an ISO-conforming HDR export function was developed. Prototypes for both of these elements were integrated into the PhotoLab codebase.
Using images generated through the proposed pipeline, psychophysical experiments were conducted, demonstrating that people have a clear preference for HDR imagery compared to SDR, and that the proposed DxO HDR methodology performs better than existing commercial techniques, such as those found in Adobe Lightroom, or those proposed by the International Telecommunication Union.
