Re: Converting 24 bit images to 8 bit images with a specific colour table

[philaldis(at)geocities.com (Phil Aldis)]

On Thu, 06 May 1999 12:13:18 -0500, Liam Gumley
<Liam.Gumley@ssec.wisc.edu> wrote:

>Phil Aldis wrote:
>> If I have a 24bit image and I want to convert it to an 8bit image
>> which uses a particular table, so find nearest values.
>> This is of particular use, when you're writing multiple gifs from 24
>> bit images, because color_quan, will obviously not work, because the
>> colour table has to be global.
>
>If you want to create a GIF which contains 2 sub images derived from 24
>bit true color images, you need to split the color table. Here's an
>example:
>

>---
>Liam E. Gumley
>Space Science and Engineering Center, UW-Madison
>http://cimss.ssec.wisc.edu/~gumley


Okay well, I should have made myself more clear. I'm currently working
on an object graphics environment , which uses direct graphics to
display. Whe you put a load of objects together, you put them into a
view object, which is like the IDLgrview object, and this can be
displayed in the window object, or sent to the postscript object.
However, I thought some gif, bmp etc. output objects would be kinda
cool.

So you'd pass the gif object a view and it would display it in a
pixmap, tvrd() the image and write it to gif. The problem is that the
only way I can be really sure of getting the right values back from a
tvrd() is to set true colour on, and get back a true colour image. So
then I want to pass this image back through the colour tables that
they have specfiied (which by default would be the current ones), and
find the closest match.

I hope I've now explained myself a bit better, and if you look at teh
code I put in with my initial post, I think it's amde a bit clearer
what I mean.

Cheers, 
Phil