Re: GIMPing and transparency

["Robert G. Brown" <bob@xxxxxxx>]

ON Sun, 07 Nov 1999 09:41:48 EST, karl rasche <rasche@cs.hope.edu> Wrote:
>to do transparency, you will need an alpha channel with your image (so,
>you will have 4 channels in total, red, green, blue, and alpha). ...
>...I do not believe jpeg has this capability, so if you're trying to
>save out transparent jpeg's, it just wont work.
OK. I don't care what the output has to be, as Long as I can convert to it.

>...look on the title bar for the image window.  does it
>say something like "foo.gif-....(indexed-alpha)" or
>"bar.jpeg-...(RGB-alpha)?
If it does, The next step can be skipped...

>if there is no -alpha, go to "layers->add alpha channel". 

>incidently, creating a new image with the "transparent" fill type adds an
>alpha channel.
Yes, but it's more steps!

>now, if there is only one colour you want to set to be transparent, go
>to "select->by color".  a window should pop up.  clicking on a colour in
>your image window will cause it to be selected, and a black and white
>representation of the selected region will be drawn.
Right, OK...

>once you have picked your favorite colour, hit "edit->clear".  the
>selected regions should now be filled with the grey and darker grey
>checkerboard pattern.
Yes, That's right...works so far...

>now, if you were to open this file in another program, say, xv, the
>transparent sections would look very wierd (i tried it on two images, one
>turned out with the areas being white, the other they were black).
I think JPEG has a "base background" color, which can be set somehow. Some
software sets it one way, others another. I'm not too interested in finding
this knob.

>since you have only one image open, what will you see when you look
>"through" the transparent image?  black? white? paisley? 
Silly Question! If it's TRANSPARENT, I expect to see the back of the monitor!
No... World Peace, or.... Toontown! :)

>if you toss it on a quick web page, you should see the background colour 
>through the transparent regions (at least in a browser that supports 
>transparent gifs).
Yes, the image type better support what you're trying to do!  This lead to 
some noodling around in GIMP, since the transformation required to take in
a JPEG, render something transparent, and save it AS A GIF is not clear. I
noodled around a bit in GIMP and found the missing part, which is to 
"Index" the image. This is done by click-right on the image, select "Image"
of the menu, and select "Indexed". A window appears, perhaps thought is
needed, but when one clicks "OK", the image can then be saved as a GIF (and
not before).

*** SUCCESS!! The saved image shows up correctly, floating on the web page
              background. This is EXACTLY the desired effect.


>oh. i think the "magic wand" that was being referred to can be found on
>left side of the toolbar, second button down from the top.
It makes sense that this would do the selection Matt mentioned. I guess its
magic since I suppose that's what is coming out of the end of the wand....

                                                         Regards,
                                                          ---> RGB <---