New builtin blender doesn't fallback to 8 bit for jpeg

[tduell]

Testing hugin-executor branch (6781:b0daf9c2446e) built on Fedora 20 x86_64.
Using two input 16 bit tiff images, builtin blender, and attempting to stitch "exposure corrected ldr" with output to jpeg.
Stitch fails, JPEH does not support requested pixel type UINT16".
When using enblend falls back to UINT8 and completes stitch OK.
The log file is as follows...
============================================
Stitching panorama...
============================================

Platform: Linux 3.17.7-200.fc20.x86_64 x86_64
Version: 2014.1.0.b0daf9c2446e
Working directory: /home/terry/Hugin/Problem-solve/MMacintosh/testcase/newtest
Output prefix: 0007-0008-builtinblender

Blender: internal
ExifTool version: 9.76

Number of active images: 2
Output exposure value: 14.9
Canvas size: 13876x7710
ROI: (4685, 1721) - (8358, 5990)
FOV: 99x66
Projection: Rectilinear(0)
Using GPU for remapping: false

Panorama Outputs:
* Exposure corrected, low dynamic range

First input image
Number: 0
Filename: /home/terry/Hugin/Problem-solve/MMacintosh/testcase/newtest/0007.tif
Size: 2836x4272
Projection: Normal (rectilinear)
Response type: custom (EMoR)
HFOV: 27
Exposure value: 14.9

Remapping and blending LDR images...
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
Warning: no TIFFTAG_SAMPLEFORMAT or TIFFTAG_DATATYPE, guessing pixeltype 'UINT16'.
caught exception:
Precondition violation!
exportImage(): file type JPEG does not support requested pixel type UINT16.
(/builddir/build/BUILD/vigra-1.9.0/src/impex/imageinfo.cxx:528)

Cheers,
Terry

[tmodes (tmodes)]

Hi Terry,

you found very fast the only issue which remained (at least which I know).
I thought that someone who is using 16 bit image will not use jpeg as output format. So I left this issue out.
Changeset feaf1a349739 provides fallback for some typical case (mostly to 8 bit for jpeg).
Some exotic conversion are left out. Let's wait if someone complains ;-)

[tduell (tduell-iinet)]

Fails to build here...

/home/terry/rpmbuild/BUILD/hugin-2014.1.0/src/hugin_base/vigra_ext/utils.h:655:35: error: 'TypeAsString' is not a member of 'vigra'
     const std::string pixelType = vigra::TypeAsString<typename DestTraits::ValueType>::result();

[tmodes (tmodes)]

Tried to fix in repository. I added an include for TypeAsString.