Re: opacity

On Wed, May 26, 2004 at 12:39:27PM -0400, Glenn Randers-Pehrson <glennrp> wrote:
> If mask.png is an opaque grayscale image,
> then composite will use its intensity when it wants opacity.
> 
> gm convert skill.eps -matte skill_with_matte.miff
> gm composite -compose copyopacity null: skill_with_matte.miff mask.png out.png

Thank you for the recipe - now I wonder if there isn't something up with
gm display..

I enclose out.png which was created with:

        gm convert -matte logo.eps logo.png
        gm convert mask.eps mask.png
        gm composite -compose copyopacity mask.png logo.png out.png

and I was confused by the outcome, because gm display out.png shows
a ragged circular outline. The whole point of using the mask, was
essentially to use the automatic antialiasing of the mask to get
semitransparent pixels and avoid seeing the pixelation. I just
viewed out.png with firefox on a windoze box, and the outline is
smooth. Bringing up the magnifier in gm display shows cells with
rgba values like (255,255,255,17) so the image really is semitransparent
(though I didn't realise at first), and I was also confused by gm
identify -verbose out.png with

  Colors: 3

      3120: (  0,  0,  0,  0)    black
       160: (102,102,102,  0)    grey40
      6720: (255,255,255,255)    #FFFFFFFF

which doesn't give the game away about the non 255 values in the
alpha channel..

Anyway, it all works in the sense that image is what I wanted.
(I can now just weep because the most popular browser can't display it)

Cheers,

Patrick

PS could gm display's output have something to do with my X setup?

  depth of root window:    24 planes
  number of colormaps:    minimum 1, maximum 1
  default colormap:    0x20
  default number of colormap cells:    256
  preallocated pixels:    black 0, white 16777215

seems there are enough colours available..