Re: [Boost-users] [GIL] planar view with different bit depth

Subject: Re: [Boost-users] [GIL] planar view with different bit depth
From: Eloi Du Bois (eloi.du.bois_at_[hidden])
Date: 2009-12-27 19:40:36

Hi Lubomir,

I will have a look on what you said, but I have found a temporarly solution:
I am using gray views to store each components of my exr image... I need to
do so because in exr, you can have an arbitrary number of channels, each one
having a different kind of pixel and / or dimension ! That is why I thought
it is better to use views... Now it is working on my project, I will try to
make a io extension for gil, but I am running out of time. I'll try because
this is not so difficult (true only with exr, dpx is very difficult).

Thank you for all and happy new year !
Eloi.

2009/12/28 Lubomir Bourdev <lbourdev_at_[hidden]>

> Hi Eloi,
>
> Think of GIL as a collection of concepts and models. The most general
> concepts support heterogeneous planar pixels (which means that GIL
> algorithms should work with them), but there are no existing models that
> provide implementation.
>
> Even though GIL has a model for pixel value whose channels are of different
> types, those types can only differ in bit depth. What you want is each
> channel to be completely different - float, uint8, etc. So we need a new
> model of pixel value, which shouldn't be too hard to do if you start with an
> existing model.
>
> Once you implement the new pixel value, there are several ways to proceed
> further depending on what functionality you want. The simplest way, if
> performance is not critical and if you require read-only model, is to create
> a new virtual image view that returns the new pixel value upon
> dereferencing. See the Mandelbrot example in the tutorial. All you need for
> this to work is to provide a function object that given (x,y) image
> coordinates, creates and returns your pixel value.
>
> If you want your heterogeneous planar view to be writable, you will also
> need to provide a model for a heterogeneous planar pixel reference that goes
> with the new pixel value model I mentioned above and return that from your
> virtual image pixel accessor. Again you can look at the several pixel
> reference proxy models that GIL comes with.
>
> If recomputing memory coordinates from (x,y) on every pixel access is too
> slow, you will also have to provide a custom pixel iterator and pixel
> locator that support heterogeneous planar pixels. See the design of custom
> pixel iterators and locators that come with GIL and the code examples. This
> will allow for a "native" GIL implementation of heterogeneous planar pixels.
>
> Lubomir
>
>
> > -----Original Message-----
> > From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> > bounces_at_[hidden]] On Behalf Of Christian Henning
> > Sent: Monday, December 21, 2009 9:23 AM
> > To: boost-users_at_[hidden]
> > Subject: Re: [Boost-users] [GIL] planar view with different bit depth
> >
> > Hi Eloi,
> >
> > I have never tried that and I'm not sure if gil is designed to support
> > such a functionality. Would be cool if you could define such a pixels
> > type with a tuple ( mpl::vector4<
> > uint32_t,double32_t,double16_t,uint8_t> ).
> >
> > But you might be able to create packed_channel_reference types for
> > each channel. But first you need to provide a 90bits integer type.
> >
> > packed_channel_reference< uint90_t, 0, 32, 1 >
> > packed_channel_reference< uint90_t,32, 32, 1 >
> > packed_channel_reference< uint90_t,64, 16, 1 >
> > packed_channel_reference< uint90_t,80,  8, 1 >
> >
> > Such channels you could combine into a pixel type.
> >
> > Mhmm, the more I think about it the more I have doubts. Hopefully
> > Lubomir has better ideas. Such funtionality should be part of gil 3.0?
> >
> > BTW, would you be interested in creating a exr io extension for gil? I
> > can help you out.
> >
> > Regards,
> > Christian
> >
> > On Mon, Dec 21, 2009 at 11:55 AM, Eloi Du Bois <eloi.du.bois_at_[hidden]>
> > wrote:
> > > Hi all,
> > >
> > > I have a question. I am using gil to read exr image files (movie
> > standard)
> > > and I would like to know can I make a planar view with n channels of
> > > different pixel bit depth...
> > > That sound weird but the exr standard allow users to put channels of
> > > different types !
> > > For example:
> > > R = unsigned int 32
> > > G = half float
> > > B = float
> > > A = byte
> > >
> > > Thank you,
> > > Eloi.
> > >
> > >
> > > _______________________________________________
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> > >
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