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From: Ullrich Koethe (koethe_at_[hidden])
Date: 2006-10-18 01:11:30

Lubomir Bourdev wrote:
> To demonstrate how GIL can be integrated with other imaging libraries, we decided to create two wrappers of imaging algorithms of another library and invoke them from GIL.
> We picked Vigra as a test case.
> Things work well only for 8-bit grayscale values. 16-bit gray sort of works ok, perhaps the only difference is the need to use different settings.
> If I use RGB values, however, canny_edge does not compile, and the Gaussian convolution returns the result in grayscale.
> Other color spaces, channel depths and planar images I am not sure how to set up.
> Perhaps I am not using Vigra properly. Prof. Köthe could you take a look at my source file (link above) and let me know if it looks OK?

I got your program to work. The 8-bit grayscale case does indeed give the
correct result. In case of 16-bit grayscale, I found that the input
grayvalues were shifted by 8 bit. I.e. instead of the value 188, the input
image contained 48316 == 188 << 8 (the input file was the same). The edges
changed accordingly. This is perhaps a byte order problem, or a bad

It failes to compile with 8-bit RGB because cannyEdgelList() is only
applicable to scalar images at the moment (the docu says
"SrcAccessor::value_type must be convertible to float"). But the
convolution example works just fine.

Compilation with 16-bit signed int also failes, because GIL doesn't define
a conversion from gray8 to gray16s (it should).

So VIGRA and GIL seem to be fairly interoperable. You should have
contributed to VIGRA instead of starting your own library ;-)


|                                                                |
| Ullrich Koethe  Universitaet Hamburg / University of Hamburg   |
|                 FB Informatik        / Dept. of Informatics    |
|                 AB Kognitive Systeme / Cognitive Systems Group |
|                                                                |
| Phone: +49 (0)40 42883-2573                Vogt-Koelln-Str. 30 |
| Fax:   +49 (0)40 42883-2572                D - 22527 Hamburg   |
| Email: u.koethe_at_[hidden]               Germany             |
|        koethe_at_[hidden]                        |
| WWW:      |

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