There is a way to do this with plain ImageInput. One variety of
ImageInput::open take a "configuration", which you can seed with an attribute
called "oiio:UnassociatedAlpha" (set to 1) that instructs the TGA reader to not
premultiply the RGB by the A.
ImageSpec config;
config.attribute ("oiio:UnassociatedAlpha", 1);
ImageInput *in = ImageInput::open (filename, &config);
const ImageSpec &spec = in->spec();
std::vector<unsigned char> pixels
(spec.width*spec.height*spec.channels);
in->read_image (TypeDesc::UINT8, &pixels[0]);
in->close ();
delete in;
There's not a very clean way to do this with an ImageBuf.
I suppose one strategy is to create a blank ImageBuf, then read into it in a
variation of the above. Instead of declaring that std::vector, you could do
this:
ImageSpec config;
config.attribute ("oiio:UnassociatedAlpha", 1);
ImageInput *in = ImageInput::open (filename, &config);
const ImageSpec &spec = in->spec();
ImageBuf buf;
buf.alloc (spec); // size it based on the input image
in->read_image (TypeDesc::UINT8, buf.localpixels());
in->close ();
delete in;
And then proceed to use the ImageBuf as you always would.
I admit this is kind of clunky. It's probably better to add some kind of method
to ImageBuf that lets you specify a "configuration" that will be applied when
the file is opened and read.
On Jun 9, 2014, at 8:56 PM, Nicolas Burtnyk <[email protected]> wrote:
> We're running into an issue with where we're using ImageBuf to read a TGA
> file which happens to have an alpha channel filled with zeros. We want to
> grab the data in the red and green channels without an premultiplication
> (otherwise they're just all 0). Is this currently possible with ImageBuf?
>
> Thanks!
>
> Nicolas
--
Larry Gritz
[email protected]
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