Re: Compositing transparent png over image using Magick++ GraphicsMagick API

Ok, good. I got proper overlay with OverCompositeOp:

  Image rose("magick:rose");
  Image watermark("watermark.png");
  rose.composite(watermark, CenterGravity, OverCompositeOp);
  rose.write("destination.gif");

Now I need to apply opacity to watermark, so that background image could be
seen through the watermark.
I tried setting watermark.opacity(MaxRGB*30/100); but transparent color is
again lost.

Basically command line that I want to implement in Magick++ is this:

gm composite -dissolve 50 -gravity center watermark.png magick:rose
destination.gif

I tried to do it with this code:

    Image rose("magick:rose");
  Image watermark("watermark.png");
  watermark.opacity(MaxRGB*30/100);
  rose.composite(watermark, CenterGravity, DissolveCompositeOp);
  rose.write("destination.gif");

but the result is not comparable (ie. letter A is transparent but the
background from watermark is black with some transparency, not clear
transparent).

Do you know any way how to accomplish this? I just need semi transparent
watermark overlayed on source image.


On Wed, Jan 29, 2014 at 2:59 PM, Bob Friesenhahn <
[email protected]> wrote:

> On Wed, 29 Jan 2014, Dragan Jotanovic wrote:
>
>>
>>     Image rose("magick:rose");
>>   Image watermark("watermark.png");
>>   rose.composite(watermark, CenterGravity, CopyCompositeOp);
>>   rose.write("destination.gif");
>>
>> but I get black pixels in place of transparent pixels from watermark.png.
>> I also tried setting rose.matte(true); and watermark.matte(true); without
>> results.
>>
>> Is there an easy way to accomplish this?
>>
>
> It seems that I provided wrong information about the default composite
> operator.  The GM manual page says that 'Over' is the default. Please use
> OverCompositeOp or AtopCompositeOp rather than CopyCompositeOp and then you
> should be happy.
>
> The command line is apparently not using CopyCompositeOp.
>
> You can test from the command line like:
>
>   gm composite -compose Atop -gravity center watermark.png rose:
> destination.gif
>
>   gm composite -compose Over -gravity center watermark.png rose:
> destination.gif
>
> vs (wrong)
>
>   gm composite -compose Copy -gravity center watermark.png rose:
> destination.gif
>
>
> Bob
> --
> Bob Friesenhahn
> [email protected], http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
>
>
> ------------------------------------------------------------------------------
> WatchGuard Dimension instantly turns raw network data into actionable
> security intelligence. It gives you real-time visual feedback on key
> security issues and trends.  Skip the complicated setup - simply import
> a virtual appliance and go from zero to informed in seconds.
>
> http://pubads.g.doubleclick.net/gampad/clk?id=123612991&iu=/4140/ostg.clktrk
> _______________________________________________
> Graphicsmagick-apis mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/graphicsmagick-apis
>
>

------------------------------------------------------------------------------
WatchGuard Dimension instantly turns raw network data into actionable 
security intelligence. It gives you real-time visual feedback on key
security issues and trends.  Skip the complicated setup - simply import
a virtual appliance and go from zero to informed in seconds.
http://pubads.g.doubleclick.net/gampad/clk?id=123612991&iu=/4140/ostg.clktrk

_______________________________________________
Graphicsmagick-apis mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/graphicsmagick-apis