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Ldr2Hdr: On-the-fly Reverse Tone Mapping of Legacy Video and Photographs
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(1) The University of British Columbia,
(2) Dolby Canada, formerly BrightSide Technologies
Abstract
New generations of display devices promise to provide significantly
improved dynamic range over conventional display technology. In the
long run, evolving camera technology and file formats will provide
high fidelity content for these display devices. In the near term,
however, the vast majority of images and video will only be available
in low dynamic range formats.
In this paper we describe a method for boosting the dynamic range of
legacy video and photographs for viewing on high dynamic range
displays. Our emphasis is on real-time processing of video streams,
such as web streams or the signal from a DVD player. We place
particular emphasis on robustness of the method, and its ability to
deal with a wide range of content without user adjusted parameters or
visible artifacts. The method can be implemented on both graphics
hardware and on signal processors that are directly integrated in the
HDR displays.
The Ldr2Hdr pipeline
Image pyramids allow efficient operations for real-time performance
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Photographs from Figure 6 of the paper
The following images are source photographs and results of the Ldr2Hdr
dynamic range expansion software. For each photograph there are 6 images.
- the original LDR image which is the input to the Ldr2Hdr program
- the final HDR image converted back to an LDR image with the Reinhard 02
tone mapping operation
- a split-screen dual exposure showing detail in both bright and dark regions;
both levels of detail are visible simultaneously on a HDR display but not
simultaneously on a LDR display
- the final HDR image in pfm format
- the final HDR image in Radiance HDR format
- the final HDR image in OpenEXR format
Original LDR Image
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HDR Tone Mapped with Reinhard 02
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HDR split-screen synthetic dual exposure
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__HDR_images__
pfm
Radiance_HDR
OpenEXR
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Viewing the HDR file formats
In order to view the HDR or OpenEXR files, you will need software
which can read and display these files. Since they are all high dynamic range
file formats and images, it will generally not be possible to see all the
features at the same time unless you have an HDR display;
the software will have a mechanism to let you
see the image at different brightness (exposure) levels which you can adjust.
The following sites provide software to view these types of files.
Discussion and Conclusions
In this paper we have presented a method for on-the-fly expansion of
the dynamic range of legacy, low dynamic range, video content for
viewing on HDR displays. The method is robust and temporally coherent,
and does not require image-specific parameter adjustment. As such the
method is well-suited for integration directly in HDR display
hardware, where it can be used to process video streams from legacy
sources such as television or DVDs.
In this paper we have focused on the space of real-time solutions to
the problem of expanding the dynamic range of LDR imagery. More
sophisticated, albeit slower methods would be interesting to explore
in the future.
Last modified: Fri Apr 29 18:49:40 PDT 2011
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