the usage of -dissolve

[vita001]

Hi,
the following images greenbox.jpg and bluebox.jpg are two boxes of different dimension. I want the greenbox to cover the bluebox. I find the -dissolve,
from http://www.imagemagick.org/Usage/compose/#blend and I want to achieve the similar result as the dissolve 100% effect which is the greenbox cover part of the bluebox. However, when I do the following, the blue box are complete gone. Any help is appreciated.

convert -size 640x640 xc:black -fill green -draw "rectangle 0, 128, 639,256" greenbox.jpg
convert -size 640x640 xc:black -fill blue -draw "rectangle 64,64,576,576" bluebox.jpg
composite -dissolve 100% greenbox.jpg bluebox.jpg gif:-|display -

[fmw42]

composite -dissolve 100% greenbox.jpg bluebox.jpg gif:-|display -

a dissolve of 100% will make one image completely cover the other. You need to specify two dissolve values or one value that is not 0 or 100%. see http://www.imagemagick.org/Usage/compose/#dissolve. Or make the background transparent and not black.

try

composite -dissolve 50% greenbox.jpg bluebox.jpg show:

[vita001]

In the given link http://www.imagemagick.org/Usage/compose/#dissolve, the dissolve 100% example show two pictures which is what I want.
How can I make the background transient?

[fmw42]

try using xc:none in your code above for your green image, so that the background is transparent like Anthony's example.

Or make the first image smaller in both dimensions than the other.

[vita001]

xc:none cannot make the background transparent. This is what I tried.

convert -size 640x640 xc:none -fill green -draw "rectangle 0, 128, 639,256" greenbox.jpg

convert -size 640x640 xc:black -fill blue -draw "rectangle 64,64,576,576" bluebox.jpg

composite -dissolve 100% greenbox.jpg bluebox.jpg gif:-|display -

[fmw42]

xc:none cannot make the background transparent. This is what I tried.

convert -size 640x640 xc:none -fill green -draw "rectangle 0, 128, 639,256" greenbox.jpg

convert -size 640x640 xc:black -fill blue -draw "rectangle 64,64,576,576" bluebox.jpg

composite -dissolve 100% greenbox.jpg bluebox.jpg gif:-|display -

JPG does NOT support transparency. Change your greenbox (and bluebox) to png. That way you don't have quality loss from jpg.


convert -size 640x640 xc:none -fill green -draw "rectangle 0, 128, 639,256" greenbox.png

convert -size 640x640 xc:black -fill blue -draw "rectangle 64,64,576,576" bluebox.png

composite -dissolve 100% greenbox.png bluebox.png show:

[vita001]

If I have a png file(which is obtained by converting a jpg files), I want to change the black background color to transparent. So I do the following:
convert test.png -fill xc:none -opaque black -fuzz 20% test.png

However, it seems not working, if I do the following
composite -dissolve 100% test.png test2.png gif:-|display -

test.png still completely covers test2.png.

Any solutions? Thanks.

[fmw42]

If I have a png file(which is obtained by converting a jpg files), I want to change the black background color to transparent. So I do the following:
convert test.png -fill xc:none -opaque black -fuzz 20% test.png

Your -fill xc:none is an invalid command.



To change black to transparent use either

convert test.png -fuzz 20% -fill none -opaque black test.png[/quote]

or better

convert test.png -fuzz XX% -transparent black result.png

Note that -fuzz must come before -transparent or -fill.

[vita001]

This one doesn't work :convert test.png -fuzz 20% -fill none -opaque black test.png
But this one does: convert test.png -fuzz XX% -transparent black result.png

Thank you very much. I finally have what I want.

[fmw42]

This one doesn't work :convert test.png -fuzz 20% -fill none -opaque black test.png
But this one does: convert test.png -fuzz XX% -transparent black result.png

Thank you very much. I finally have what I want.

The first one should be working as I thought it had been fixed. You can make it work by


convert test.png -channel rgba -fill none -opaque white result.png