Re: [boost] GIL Review - Integration with other graphics libraries, such as Cairo.

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 
reinterpret_cast?

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 ;-)

Regards
Ulli
-- 
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