| From: | Keith Halstead |
| Date: | 13 Oct 99 at 13:35:11 |
| Subject: | Re: Numeric Transparancy |
From: Keith Halstead <keith@halsteadk.freeserve.co.uk>
Hi Dave,
On 13-Oct-99, you wrote:
> Sorry if this is a dumb question, but when making a transparent
> gif, how does one make a colour other than black transparent. I
> know Black is colour "0" (well it is in ImageStudio anyway) so
> what number is white, or yellow, or whatever else.
See also Don Cox's reply. The important thing to realise is that gif's can
have up to 256 colours specified and each of these can be any colour. So
colour "0" could be any colour and there is no particular colour/palette
number that is a particular colour. You can make only one of these palette
numbers transparent.
There is a handy little command-line program on Aminet called "webgif" which
can make a certain palette number transparent and/or make the gif interlaced
and also output a list of all the colour numbers with the RGB values. So if
you know you want white to be transparent you just look down the list for
RGB=255,255,255 and that will give you the palette number you want.
However, as Don says you'd need to be careful that you don't have two palette
numbers specifying the colour you want to make transparent, as you can only
make one palette number transparent. Of course this might be useful if, say
you wanted the white background of your gif to be transparent, but there were
other white bits you didn't want to be transparent. A program like Personal
Paint is handy here as you can see what colours are in the palette. You can
also easily see whether your transparent bit is all defined by one colour.
So if you wanted to make the first colour in your image the transparent colour
you'd type something like:
webgif -t 0 image.gif
E-mail me personally if you want any more help, or I can send you the
executable (it's small). Also, I have a CLI convertor ("makegif") from
ILBM->GIF which you may find useful if you only have PPaint from a coverdisc
which can't save GIFs.
Regards,
Keith
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