Great.
Is this a common enough problem that we should have a direct way to tell
ImageBuf to do this upon load? Or is it a one-time edge case you just needed a
workaround for and will probably not recur?
-- lg
On Jun 13, 2014, at 11:02 AM, Nicolas Burtnyk <[email protected]> wrote:
> Thanks Larry,
>
> We went with a variation on technique #2.
>
> Cheers,
>
> -Nicolas
>
> On Thu, Jun 12, 2014 at 10:12 AM, Larry Gritz <[email protected]> wrote:
> 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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