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