I am completely new to Fireworks, having worked for years in Photoshop. Sorry if I am asking about a simple/standard procedure, but it wasn't readily apparent to me in my first try in Fireworks.
I am trying to create an image file for use in an astronomical visualization package called Celestia. To map clouds onto a planet I'd like to be able to take a grayscale image like this:
and convert the darker portions to transparent, with the grayscale level scaling to differnt levels of opacity (white = opaque, black=transparent).
Celestia can read .jpg and .png image files for surface texture maps and cloud maps. Is there any way to bring in a Photoshop .psd file with an image like this as an alpha channel and use the alpha channel info to save a single layer .png file with varying levels of opacity?
Well, one way is to open the file in Fireworks and then from the filter menu choose Other > Convert to Alpha.
Then set your canvas color to transparent (in the Properties panel), and Export the file as a PNG 32. That should maintain the alpha transparency.
Let me know if that works for you.
This did indeed work to produce just the result I was looking for.
One minor difference from what I was expecting: the Celestia files assumed that black would go to transparent and white would remain opaque. The "convert to alpha" within Fireworks takes white to transparent instead. But no problem - I just inverted the original image file first, ran the "convert to alpha" filter option, and then inverted the resulting image again within Fireworks before saving out as a .png file. Loaded into Celestia the resulting cloud image file worked just as I've been wanting.
Thanks again - very helpful!