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March 1994

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1994.03.08 22:08 "Re: NeXT to standard X11 Image/Pixmap (really bug in TIFFWriteDirectory)", by Sam Leffler

    To:  Sam Leffler <sam>
    Subject:  Re: NeXT to standard X11 Image/Pixmap 
    Date: Mon, 07 Mar 1994 22:23:01 EST
    From:  Matt Willis <willis@euclid.stetson.edu>

    
    
    On Mon, 7 Mar 1994, Sam Leffler wrote:
    
    > If you told me how you were trying to do this I might be able to
    > help.  I don't recall if tiffcp extracts alpha or not.  If not it
    > would seem to be logic place to start.
    > 
    >     Sam
    > 
    
    Both tiffcp and tiffsplit strip out the Alpha values. I'm adding 
    a uuencoded sample NeXT tiff to show what I mean...
    
    I'm running tiffsplit on the file, to seperate out the black and white 
    and color images... then converting the color image to be displayed, but 
    I need the alpha values to be preserved...
    
Your problem turns out to be a bug in the directory writing code;
the alpha *data* are actually present in the file.  Apply this
patch to tif_dirwrite.c to insure the ExtraSamples tag is written.

	Sam

*** 1.31	1993/08/26 14:24:07
--- tif_dirwrite.c	1994/03/08 22:03:48
***************
*** 163,169 ****
  	 * Write out ExtraSamples tag only if
  	 * extra samples are present in the data.
  	 */
! 	if (FieldSet(fields, FIELD_EXTRASAMPLES) && td->td_extrasamples) {
  		ResetFieldBit(fields, FIELD_EXTRASAMPLES);
  		nfields--;
  		dirsize -= sizeof (TIFFDirEntry);
--- 163,169 ----
  	 * Write out ExtraSamples tag only if
  	 * extra samples are present in the data.
  	 */
! 	if (FieldSet(fields, FIELD_EXTRASAMPLES) && td->td_extrasamples == 0) {
  		ResetFieldBit(fields, FIELD_EXTRASAMPLES);
  		nfields--;
  		dirsize -= sizeof (TIFFDirEntry);