CompuServe Messages

#Reversed TIFF Files

    31-Dec-88 17:51:10
Sb: #7536-#Reversed TIFF Files
Fm: Steve Werner 72126,727
To: Thom Hartmann 70007,1176
What scanner software is producing the TIFF files that are not inverting properly? It may not be QuarkXpress' fault. I've seen it happen a couple times too, and it was in PageMaker as well. What I believe the problem is that the scanner software is incorrectly changing the "settransfer" function, although I haven't investigated the cases where it happened to me thoroughly enough to be entirely sure. I'll quote from an essay on "Writing Device-Independent PostScript" from my favorite book of the week, Real World PostScript. "For example, reverse image (black for white and white for black) requires only a simple change to the transfer function. The typical mistake the [programmer] makes is to simply replace the current transfer function, reasoning that 'The default transfer function doesn't do anything anyway.' Of course, the fallacy is that you don't really know what your initial context is. Your program may be part of a composite document, or might be sent to a printer with an atypical default transfer." The author, Michael Fryd, goes on to suggest that the correct way to change the transfer function is to modify the current function not replace it. (p. 55). To test this out: (1) try a different scanner's software or (2) try placing the TIFF in another program (PageMaker or ReadySetGo! and see if you get the same result. Let me know what you find out.