Re: [boost] VIGRA - Image processing for boost

From: Ullrich Koethe (u.koethe_at_[hidden])
Date: 2001-11-15 14:04:57

Peter Dimov wrote:
> 
> From: "Ullrich Koethe" <u.koethe_at_[hidden]>
> > Peter Dimov wrote:
> > > The interface as presented to the user would be orthogonal:
> > >
> > > basic_image<bool, linear> // == basic_image<unsigned char, linear>
> > > basic_image<bool, packed> // == vector<bool>
> > > basic_image<bool, rle>
> > > basic_image<unsigned char, linear>
> > > basic_image<unsigned char, rle>
> >
> > So you would specialize algorithms on storage format (linear, packed,
> > rle)? Interesting, but a lot of work (some algorithms are needed 3
> > times).
> 
> Only where it makes sense.
> 
> Look at it this way. The choices are:
> 
> [1]
> 
> basic_image<T> - linear
> packed_image // always bool
> rle_image // always bool
> 
> [2]
> 
> basic_image<T>
> basic_image<packed_bool>
> basic_image<rle_bool>
> 
> or [3] - see above.
> 
> The difference is that in [3] you may choose what to specialize and what to
> leave to the generic version to handle.
> 

Since I'm using iterators, I'll have to specialize on iterator type. So,
iterator traits must contain the storage formats of the corresponding
container. Looks workable.

> > No, I also have accessors for variable band formats (SequenceAccessor,
> > VectorAccessor and VectorBandAccessor)
> 
> True, but having
> 
> image<std::vector<unsigned char> >
> 
> would be quite inefficient since the vectors won't exploit the fact that
> they are the same size. Or am I missing something.
> 

Yes, because the accessors only require a vector _interface_. So you can
define a

vector_image<unsigned char>

that allocates a contigous block of memory, and considers stretches of n
values as one pixel. The iterator would then return an appropriate proxy
that implements the required interface on top of this. (Which brings me
to proxies, who would warrant a discussion of their own...)

Ulli
-- 
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