Re: [Plib-users] Transparent Background

[Steve B. <sjb...@ai...>]

Alexander Rawass wrote:

> I have some pictures I like to use as explosion, galaxies, background
> image etc.,
> but I need their background to be transparent, instead of color black.
> 
> I did load one of those into gimp, and gimp showed me that the picture
> had
> no alpha channel, and that the background was indeed black not
> transparent.

In GIMP, do this:

  1) Add an alpha channel.
  2) Under the 'select' menu, choose 'Select by colour'
  3) Click on some nice large black area - it'll select all the black
     in the image and you can wipe it out (to transparent) simply by
     clicking on 'cut' in the 'Edit' menu.
  4) By playing with the slider in the select/by-colour menu, you
     can control just how close to the colour of the pixel you
     clicked on will be selected.
  5) If that doesn't work well (eg there are also other dark areas
     that you want to keep - but you still have a dark 'halo' around
     the image) - then do a 'grow' in the select menu to increase the
     'thickness' of the selection before you hit 'cut'.
  6) UNDO (control-Z) can be your friend!  Use it!

> Or can I say GL/plib to load an object/image an declare color black as
> transparent?

No - I think GIMP is good enough to do this right.

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