image corruption

  • Thread starter Thread starter Graeme Ambrose
  • Start date Start date
G

Graeme Ambrose

When applying a transparency to a colour in a tiff or jpg
image, the image corrupts when being printed to a
postcript printer. Printing using PCL works fine except
the print loses a lot of detail.
Any thoughts on this corruption issue. It happens in PP97
and PP2000.
TIA
 
When applying a transparency to a colour in a tiff or jpg
image, the image corrupts when being printed to a
postcript printer.
Click to expand...

If you apply alpha transparency to a TIFF or PNG before bringing it into
PPT, it won't print properly to PS; the 8-bit transparency mask gets
converted to a 1-bit mask (ie, all grays below the midpoint go black, all
grays above go white, transparency becomes strictly on/off rather than
gradual).

If you're applying transparency within PPT to JPGs using the transparency
tool (let's leave TIFFs out of the mix for now), then what printer are you
printing to?

What settings are you choosing in the print dialog; what operating system
version?

What's on the background of the slide?

Works ok here, though depending on the image and the background, you may or
may not get a lot of "fringing" effects at the border between the
transparent and visible pixels.
 
I am printing in colour to a variety of Tektronix colour
printers, both laser and solid ink using Windows98.
The images are on a white backgound and the corruption is
horizontal streaks through the images as though you are
running out of toner. These streaks are in the same place
on the image no matter where it is on the page or how big
it is.
The transparency is applied within PP.
regards
Graeme
 
We were printing in standard mode, not enhanced. Why
should it make a difference?. Is this type of problem
endemic to Tek printers? or is it powerpoint coming to
terms with postscript?
Click to expand...

It's PowerPoint, not PS or the printers. The PostScript that comes out of
PowerPoint when you invoke certain features (transparency, gradients in
particular) could best be described as "stupidity applied with brute force"
;-)

Particularly, where smarter PS would query the printer it's running on to
get the current resolution and adjust what it does accordingly (hey, it's a
programming language, it can DO this stuff ... that's what makes it so
useful) PPT's PS simply assumes a set resolution and forges onward.

Problem is, if the printer and assumed resolutions don't match (as they
might not in enhanced mode) then things get ugly, and one of the results is
horizonatal white lines through gradients and transparencies.

I'd try changing the driver settings on the Tek to see if changes in
resolution and other such features can't solve the problem.
 
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