dcm2img now determines output format automatically.

The output image format is now by default determined from the
file name extension of the given output filename.
Furthermore, refactored the code that handles the (many)
image processing options into functions in order to decrease
the size of the main() routine.

dcmapps/docs/dcm2img.man

@@ -15,10 +15,9 @@ dcm2img [options] dcmfile-in [bitmap-out]
 \section dcm2img_description DESCRIPTION
 
 The \b dcm2img utility reads a DICOM image, converts the pixel data according
-to the selected image processing options and writes back an image in the
-well-known PGM/PPM (portable gray map / portable pix map), PNG, TIFF, JPEG
-(Joint Photographic Experts Group) or Windows BMP format.  This utility
-supports uncompressed as well as JPEG, JPEG-LS and RLE compressed DICOM images.
+to the selected image processing options and writes back an image in one the
+following general purpose image formats: BMP, PGM/PPM, PNG, TIFF, JPEG, or JPEG-LS.
+This utility supports uncompressed as well as JPEG, JPEG-LS and RLE compressed DICOM images.
 
 \section dcm2img_parameters PARAMETERS
 
@@ -438,8 +437,16 @@ filename generation (only with --frame-range or --all-frames):
 
 image format:
 
+  +oa   --write-auto
+          determine file format from filename extension
+          (default for files)
+
+  # if the output filename contains no extension or an
+  # unknown/unsupported one, a warning is printed an a
+  # BMP file is written (see --write-bmp).
+
   +op   --write-raw-pnm
-          write 8-bit binary PGM/PPM (default for files)
+          write 8-bit binary PGM/PPM
 
   +opb  --write-8-bit-pnm
           write 8-bit ASCII PGM/PPM (default for stdout)