[magick-users] gradient to transparency

[Ross Presser]

I really must remember to use "Reply All" with this list.

Anyhow, I answered my own question:  add a "-negate" right after the -gamma
1.0 expression.  Then the red is opaque and the white is transparent.
   http://rpresser.googlepages.com/test2.html

This is a very interesting effect.

On Fri, Apr 11, 2008 at 3:53 PM, Ross Presser <rpresser at gmail.com> wrote:

> Following along here ... this did not do what I was expecting.
>
> convert \( -size 100x100 gradient:red \) \
> >        \( +clone -colorspace Gray -gamma 1.0 \) \
> >        +matte -compose Copy_Opacity -composite out.png
> >
>
> The result of this is that the image is pale red and transparent at the
> top, slightly darker red and less transparent in the middle, and totally
> white and opaque at the bottom. I was expecting an image that was opaque and
> red at the top, and completely transparent at the bottom.
>
> I put up a sample HTML page showing this out.png over top of a futurama
> image:
> http://rpresser.googlepages.com/test.html
>
> This may be what Christoph wanted, I dunno. But how would I do the other
> thing?  I'm picturing that the red channel value and alpha channel value
> would be identical throughout.
>