V. Future Work

The authors are considering several areas for future work. One is the use of the OpenEXR file format for storage and display and authoring tools that can take advantage of this file format. While there is an SDK for reading and displaying the images, there is no publicly available windows based implementation of an exporter. To do this we are thinking of writing a plug-in for HDRShop. We would also like to experiment with additional tone mapping operations. This article presents one well suited to today's graphics hardware, but other techniques may be more suitable, depending on desired effect.

Finally, we would like to experiment with per-pixel tone mapping. [Reinhard02] discusses a technique to simulate the photographer's use of dodge and burn. Dodge and burn is the action of adding or subtracting light from areas in the print to increase or limit exposure, usually done with a piece of article with a hole cut out or a small wand. Think of it as choosing a key value for every pixel. Since we wanted a fast tone mapping technique we chose not to focus on this operator, but as graphics hardware becomes faster per pixel tone mapping operators will surely be able to be done in real-time. Another alternative to consider is the application of a tone mapping in regions of luminance values by determining local keys to apply either the per pixel tone mapping or the average luminance value operator we described in detail above.

VI. References

[Akenine-Moller02] Tomas Akenine-Moller and Erik Haines. Real-Time Rendering, 2^nd Edition. Page 193. AK Peters. 2002.

[Cohen01] Jonathan Cohen, Chris Tchou, Tim Hawkins, and Paul Debevec. Real-Time High Dynamic Range Texture Mapping. In Rendering Techniques 2001. S. J. Gortler and K. Myszkowski, eds. 313-320.

[Debevec97] Paul Debevec, Jitendra Malik. Recovering High Dynamic Range Radiance Maps from Photographs. SIGGRAPH 1997. 1997. Pages 369-378.

[Debevec02] Paul Debevec. Image-Based Lighting. Computer Graphics and Applications. March/April 2002. Pages 26-34.

[Ferwerda96] James A. Ferwerda, Sumanta N. Pattanaik, Peter Shirley, and Don Greenberg. A Model of Visual Adaptation for Realistic Image Synthesis. SIGGRAPH 1996. Pages 249-258.

[Halsted93] Charles Halsted. Brightness, Luminance, and Confusion. Information Display. 1993. http://www.crompton.com/wa3dsp/light/lumin.html.

[HDRShop04] Software for creating, editing, and saving HDR imagery. http://www.ict.usc.edu/graphics/HDRShop/. 10/29/2004.

Kawase03] Kawase, Masaki. Framebuffer Post-Processing Effects in DOUBLE S.T.E.A.L. (Wreckless). Presentation. Game Developers Conference 2003.

[Kawase04] Kawase, Masaki. Practical Implementation of High Dynamic Range Rendering. Presentation. Game Developers Conference 2004.

[MSSDK04] Microsoft Corporation DirectX 9.0 SDK Summer 2004 Update. http://www.microsoft.com/downloads/search.aspx?displaylang=en&categoryid=2. August 2004.

[Northrop04] Northrop, Cody. High Dynamic Range Lighting Brown Bag Presentation. Intel Brown Bag Lunch. 5/26/2004.

[OpenEXR04] The OpenEXR web site: http://www.openexr.org/downloads.html. August 19, 2004.

[Photogenics04] http://www.idruna.com/downloads.html.

[Probe04] Light Probe Image Gallery. http://athens.ict.usc.edu/Probes/. 9/8/2004.

[Radiance04] http://radsite.lbl.gov/radiance/HOME.html. Radiance Imaging System. August 2004.

[Reinhard04] Erik Reinhard, Personal Email Communication. July 30, 2004.

[Reinhard02] Erik Reinhard, Michael Stark, Peter Shirley, and James Ferwerda. Photographic Tone Reproduction for Digital Images. SIGGRAPH 2002. Pages 267-276.

[Shastry99] Anirudh S. Shastry. High Dynamic Range Rendering. http://www.gamedev.net/columns/hardcore/hdrrendering/.

[Seetzen04] Seetzen, Helge, Wolfgang Heidrich, Wolfgang Stuerzlinger, Greg Ward, et. Al. High Dynamic Range Display Systems. 2004 ACM Transactions on Graphics, Volume 23 Number 3. SIGGRAPH 2004. Pages 760-768.

[Ward03] Greg Ward. Global Illumination and HDRI Formats. SIGGRAPH 2003 Course #19: HDRI and Image Based Lighting. SIGGRAPH 2003.

[Walter04] Bruce Walter. RGBE File Format. http://www.graphics.cornell.edu/~bjw/rgbe.html. 2004.

Appendix A: A Simple Tone Mapping Implementation

//no warranties, expressed or implied, free for re-use
#include "stdafx.h"
#include "math.h"

#define N 11
#define delta 1.0f
#define MIDDLE_GRAY 0.36f
#define MAX_RGB 2048.0f
#define MAX_LUMINANCE ((0.2125f*MAX_RGB)+(0.7154*MAX_RGB)+(0.0721f*MAX_RGB))

// assume we have converted from RGB to luminance as described in the paper
float L[] ={  0.0f, 1.0f, 3.0f, 7.0f, 15.0f, 31.0f, 63.0f, 127.0f, 255.0f,
511.0f, 1023.0f, 2047.0f};

/* L refers to Luminance, wanted to fit on a page */
float L_NormalizedFloats[N];
float scaled_L[N];
float final_L[N];
int final_pixel_vals[N];

void _tmain(int argc, _TCHAR* argv[])
{
  float sum = 0.0f;
  float log_avg_L = 0.0f;
  float a = MIDDLE_GRAY;

  for(int i=0;i<N;i++)
  {
    float max = 0.0f;
    max = (float)MAX_LUMINANCE;
    L_NormalizedFloats[i] = L[i]/max;
  }

  for(int i=0;i<N;i++)
  {
    sum += (float)log((double)(L_NormalizedFloats[i]+1.0f));
  }

  log_avg_L = (1.0f/((float)N));
  log_avg_L *= exp(sum);
  float weight = 0.0f;
  weight = a/log_avg_L;

  for(i=0;i<N;i++)
  {
    scaled_L[i] = (weight*L[i]);
  }

  for(i=0;i<N;i++)
  {
    final_L[i] = scaled_L[i]/(1.0f+scaled_L[i]);
    int intL = (int)(final_L[i]*255.0f);
    printf("[%d] = %f %d\n",i,final_L[i]*255.0f, intL);
  }

}