Re: [boost] VIGRA - Image processing for boost

From: Ullrich Koethe (u.koethe_at_[hidden])
Date: 2001-11-20 10:27:59

Hi Michiel:
> 
> >
> > Providing two image types would be easy, but I have doubts whether it
> > will buy much. Consider the possibilities:
> >
> > * Image<bool> is unpacked. Than you can just as well use Image<byte>
> 
> That's untrue; Image<unsigned char> has (should have) operator+ and
> operator&& with semantics differing from Image<bool>.

operator&& and operator|| have the correct semantics in both cases.
operator+ shouldn't be used with bool (you can use operator^ instead).

> Furthermore,
> you can't pass a pixel of Image<unsigned char> to foo( bool& ).
> 

On g++, this doesn't work with std::vector<bool> either, because
std::vector<bool>::operator[] returns a proxy (type _Bit_reference).

BTW, on g++ 'sizeof(bool) == 4'. So Image<unsigned char> will be smaller
than Image<bool> unless the latter is packed, with all problems that the
use of proxies implies.

> Well, this is the same problem as with vector<bool>: Even the standard
> doesn't provide algorithm specializations for vector<bool>::iterator. I do
> think that the needs of image processing on 1-bit images warrant
> writing these specializations, at least for basic operations. Complex
> algorithms should be based on simple operations; let the compiler do
> the inlining.
> 
> Of course, one of the advantages of boost / open source is that you can
> just leave such work to the first person who needs it done.
> No money == much less obligations.
> 

;-) So, is anyone in need of specialized functions for Image<bool>?

Regards
Ulli
-- 
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| Ullrich Koethe  Universität Hamburg / University of Hamburg    |
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