[ptx] VIGRA and alpha channel

[Pablo d'Angelo]

On Sun, 02 May 2004, Andrew C Mihal wrote:

> Hi,
>     I've been looking at porting enblend to use VIGRA for image import and 
> export, so that we can work with 16-bit images and the other formats that 
> are available. Oddly, support for RGB + Alpha images seems to be absent 
> from vigra (I've been looking in tiff.hxx).

This is unfortunately true. I've written my own extension of tiff.hxx to
save images with alpha channels, but I haven't written functions to load
them yet. I need to do this anyway, because I'd like to respect the masks
of input images during stitching.

Actually in the current version of nona (to be checked in soon), I have
separated the alpha channel and the RGB (or grey) channels, because I think
float or 16 bit alpha channels are a waste of space (usually, just a binary
mask would be sufficient).

> I suppose that a full set of RGBA accessors, iterators, etc. would be
> necessary. Has anyone made these already? Is there a better way to do
> this?

Hmm, there are vector valued images, but proper handling of alpha channel
tiff's is not that simple with the current tiff.hxx of vigra. I'll tell you
more this evening.

ciao
  Pablo