Path: utzoo!attcan!uunet!wuarchive!csd4.csd.uwm.edu!bionet!agate!ucbvax!bloom-beacon!DELTA.ECN.PURDUE.EDU!luj
From: luj@DELTA.ECN.PURDUE.EDU (Jun Lu)
Newsgroups: comp.windows.x
Subject: Re: Fwd: How to get RGB values from XImage data
Message-ID: <8909020431.AA13449@delta.ecn.purdue.edu>
Date: 2 Sep 89 04:31:54 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 46


Thanks for your explanations.

>
>The file format used by xwd is "documented" in the header file
><X11/XWDFile.h> plus the xwd/xwud code.  The contents, in order:
>	header
>	name
>	color data
>	image data
>The pixel values in the image data index the colormap (described
>by the color data) to yield RGB values.  The exact method of indexing
>depends on the visual class described in the header, and potentially
>on the RGB masks in the header.  However, for a 24-bit DirectColor
>image, assuming you have a vanilla MIT R2 or R3 xwd (Ardent may have
>fixed this), the color data will not be present in the file.  In
>that case, you can just use the RGB masks in the header to directly
>decompose each pixel value into RGB subfields.  Other entries in the
>header (byte_order, bitmap_unit, bitmap_pad) give the details of how
>the pixels are stored in the image data.  Formats are described in
>the X protocol document (page 357 in the Digital Press book).
>

Conceptually, I know how to get the RGB values: Convert the (XImage*)->data, via color map stored, to the RGB values. However my C experince is no more than 3 months and my X experince is no more than 1 month; as a result the details are quite opaqe to me: the XPutImage.c code is quite complicated for me understand it and xwd/xwud souce codes , simple though, don't give much hints as to how to solve my problem at hand. 

Now suppose that I have a disk file data.img created by xwd. How do I go about the problem?

	/* open the disk file */

	/* read the header, color map */

	/* read the XImage data */
	/* ? !!!!!!!!!!!!!!!!!!!!!!!
	     How to get the RGB values ? 
	     i.e. How to make use of the XImage data and the color map ?
	     Any examplenary fragments of code about how actually doing this
	     coversion( on any system )  would be very helpful !!!
	? */

Another question: how to specify the plane masks in the XImage so that I can port the XImage data created from one machine to another machine ??

Are Xperts at MIT going to develop utilites for above-mentioned converstion and include them in the future X11R3+ release ?

Thank you.

Jun S. Lu