transparency; IM & carthographie

[paul]

I started using ImageMagick 2 days ago (ImageMagick 6.2.4 10/02/07 ). I am a very newbie.
My needs are working with images (png and eps) generated from GRASS (http://grass.itc.it/).
My question:
how can I get a fully transparent png image?
With the command:

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convert -transparent red base.png pippo.png

only red color is made transparent.
How can I set every colors transparent (all image)? Is there any way to get an image with a percentage of transparency ?
Does anyone know where can I find examples of IM usage in cartography?

Many thanks in advance.

[Bonzo]

I do not know what your final image needs to be but if you want to overlay your transparent png onto another image you can use:

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composite -dissolve 30% original.png background.jpg output.jpg

An example but tiling the png over the image.


You can use -watermark but that converts your png to grayscale.

[anthony]

Both dissolve and blend can make the whole image semi-transparent. Can by adjusting the parameters you don't need to overlay it onto another image. See IM Examples on Blend for an example.
http://imagemagick.org/Usage/compose/#blend_use

For partical transparency, you will need to extract and adjust the mask of an image. A grey scale value in a mask is semi-transparent!
http://imagemagick.org/Usage/channels/#erase

For selecting more colors than pure red, you would use a -fuzz factor,
http://imagemagick.org/Usage/color/#fuzz

[paul]

Hi

Bonzo, Anthony many thanks for your answers.

Paul