Vision Workbench release week synchronization.

Added a lookat and H vector to the Linescan model.

Added HDR documentation first draft.

docs/workbook/camera_module.tex

@@ -196,11 +196,6 @@ \subsection{Built-in Camera Models}
 
 \subsubsection{Pinhole Cameras}
 
- % Yakimovsky, Y. and Cunningham R., "A System for Extracting
- % Three-Dimensional Measurements from a Stereo Pair of TV
- % Cameras". Computer Graphics and Image Processing 7,
- % pp. 195-210. (1978)
-
 The {\em CAHV camera model} has been widely used in NASA planetary mission
 for rover navigation and scientific camera systems
 \cite{yakimovsky78}.  It is a basic pinhole camera model: it does not
@@ -275,13 +270,9 @@ \subsubsection{Linescan Cameras}
  \end{center}
   \label{fig:pinhole}
   \caption{Geometry of the Linear Pushbroom Camera Model.  Credit:
-    Rajiv Gupta and Richard Hartley \cite{Gupta97}.}
+    Rajiv Gupta and Richard Hartley \cite{gupta97}.}
 \end{figure}
 
-%  Rajiv Gupta and Richard Hartley. Linear Pushbroom Cameras.  IEEE
-%  Transactions on Pattern Analysis and Machine Intelligence. Vol.19
-%  No. 9. September 1997
-
 The geometry of the linescan imager is subtly different from the
 geometry of the pinhole camera.  See Figure \ref{fig:pushbroom}.
 Although there is still a center of projection created by the camera's
@@ -306,3 +297,86 @@ \subsubsection{Linescan Cameras}
 orientations.
 
 
+
+\subsection{Exif Exposure Data}
+Digital cameras store data about the settings used to take a picture
+in the image file according to the Exif standard \cite{exif}. Exif
+data is stored using the Image File Directory system described in the
+TIFF 6.0 standard \cite{tiff}.  Exif tags such as FNumber and
+ExposureTime can be used to calculate the exposure the picture was
+taken with. Unfortunately the standard is redundant and often poorly
+supported by camera manufacturers (for example, many hide the ISO
+setting in the maker note instead of storing it in the ISOSpeedRatings
+tag).
+
+The HDR module includes C++ classes ExifData (defined in ExifData.h and ExifData.cc) and
+ExifView (defined in ExifView.h and ExifView.cc) for extracting Exif data from images.
+Currently they can handle JPEG and TIFF image files. ExifData gives relatively low-level
+access to any data stored as an Exif tag, keyed by its unique tag ID (most of these have
+\#define's in ExifData.h for readability). ExifView has functions to determine some more
+commonly used camera info, checking all relevant Exif tags. ExifData and ExifView were
+based on code from jhead, an Exif Jpeg header and thumbnail manipular program in the
+public domain \cite{jhead}.
+
+\begin{verbatim}
+/*  Attempt to read flash setting. */
+ExifData data;
+int flash;
+if (data.import_data(``img.tif'')) {
+  if (data.get_tag_value(TAG_Flash, flash)) {
+    // ...
+  }
+}
+
+/* Reliably get F number. */
+ExifView view;
+if (view.load_exif(``img.jpg'')) {
+  double f = view.get_f_number();
+  // ...
+}
+\end{verbatim}
+
+\subsection{Using HDR Stacks}
+The HDR module has a set of free functions that make stitching a stack of LDR
+images into an HDR image as simple as one function call. process\_ldr\_images (in 
+LDRtoHDR.h) takes a std::vector of ImageViews (with grayscale or RGB pixels
+and a floating point channel type), sorted from darkest to brightest. This
+function assumes a constant exposure ratio between images; it can be specified
+or the default of $\sqrt{2}$ can be used for stacks with a ratio of 1 EV. An
+overloaded version also accepts a std::vector$<$vw::Vector$<$double$>$ $>$ by reference,
+to return the estimated response curves for each channel.
+
+\begin{verbatim}
+/* Generate HDR image from HDR stack. */
+typedef ImageView<PixelRGB<double> > Image;
+vector<Image> images(num_images);
+// ... Read input images ...
+// Assume default exposure ratio.
+Image hdr_image = process_ldr_images(images);
+\end{verbatim}
+
+LDRtoHDRExif.h further defines process\_ldr\_images\_exif, which generates an HDR
+image from an array of filenames of LDR images, computing brightness values
+from the files' Exif data. Example code usingthis function is in Appendix B. It
+also defines another overloaded version of process\_ldr\_images that takes a
+std::vector$<$double$>$ of brightness values (as defined by the APEX system \cite{apex})
+instead of a constant exposure ratio. These functions do not require the images
+to be in any particular order of have a constant exposure ratio.
+
+\begin{thebibliography}{1}
+
+\bibitem{exif} ``Exchangeable image file format for digital still cameras: Exif Version 2.2'',
+(Japan Electronics and Information Technology Industries Assocation, 2002),
+http://www.exif.org/specifications.html.
+
+\bibitem{gupta} Gupta, Rajiv and Hartley, Richard. ``Linear Pushbroom Cameras''.  IEEE
+ Transactions on Pattern Analysis and Machine Intelligence. Vol.19 No. 9. September 1997
+
+\bibitem{jhead} Wandel, Matthias, ``Exif Jpeg header and thumbnail manipulator program,'' 2006,
+http://www.sentex.net/~mwandel/jhead/.
+
+\bibitem{yakimovsky78}  Yakimovsky, Y. and Cunningham R., ``A System for Extracting
+  Three-Dimensional Measurements from a Stereo Pair of TV Cameras ''
+  Computer Graphics and Image Processing 7, pp. 195-210. (1978)
+
+\end{thebibliography}