Re: [Boost-users] [GIL] Premultiplications when using color_convert

Subject: Re: [Boost-users] [GIL] Premultiplications when using color_convert
From: Eloi Du Bois (eloi.du.bois_at_[hidden])
Date: 2010-04-18 08:32:50

Yes sorry, the example was quickly written.
In some cases, alpha is zero but we want to keep the pixel data, that why I
would like to disable premultiplication.

2010/4/12 Lubomir Bourdev <lbourdev_at_[hidden]>

>  Hi Eloi,
>
> One solution is to define your own color space “rgba_premultiplied_t” and
> provide color conversion functions from/to it.
>
> In your example, did you mean to use rgba32f_pixel_t ?  Also wouldn’t
> p1[3]=0.0f set the alpha to zero? In this case the color is fully
> transparent. I am not sure what you would expect...
>
> Lubomir
>
>
>
> On 4/12/10 6:38 AM, "Eloi Du Bois" <eloi.du.bois_at_[hidden]> wrote:
>
> Hi all,
>
> I am working on rgba32f view that have alpha values of 0.
> I need to apply a color_convert but it drops the values because of the 0
> alpha valued.
> How can I disable alpha premultiplication ?
> If impossible, it should be a good idea to give a choice on
> copy_and_convert & color_convert.
>
> code sample:
> rgb32f_pixel p1, p2;
> p1[0] = 1.0f;
> p1[3] = 0.0f;
> color_convert(p1, p2);
> assert(p1[0] == p2[0]);
>
> Thank you by advance,
> Eloi Du Bois.
>
>
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