Re: RGBA image mode (patchset #1589067)

[<tim...@en...>]

Ethan A Merritt wrote:
> On Saturday 05 May 2007 15:03, Ethan A Merritt wrote:
>   
>> Even after fixing a bug in unpacking the alpha channel in gp_cairo.c,
>> I can't get the wxt/cairopdf implementation of this patch to work properly.
>> I'm thinking that maybe the sub-pixel antialiasing in the cairo library is
>> messing things up. 
>>     
>
>   
See the fix on the patch page on sf.net.

> Recent versions of cairo provide a routine cairo_paint_with_alpha( image, alpha )
> This seems to work, but it applies the same alpha value to the whole image,
> not a pixel-by-pixel value.
>
> That causes me to wonder, do we really need a full RGBA format?
> For real-world usage it might be sufficient to apply the alpha value 
> from "set style fill transparent ..." to the whole image.
>
> It gets right back to the question of what an alpha channel capability
> would really be used for.
>
> Let's throw it back to the mailing list:
>
> Hey everyone,
>
> If it were possible to handle a separate alpha channel (partial transparency)
> in gnuplot's  "with image" or "with rgbimage" mode, what would you use it for?
>   
I've tried to think about that for a little while, and unfortunately I 
cannot think of anything related in my plotting experiences. However, 
the concept of layers (with an alpha channel, obviously) is pretty 
powerful as far as drawing programs are concerned. I would be surprised 
if this, applied to gnuplot, would be of no value.

Thanks for your work on this. Best regards,

Timothée