202795 - Transparency not preserved when printing

Status: REOPENED

(Core :: Printing: Output, defect)

Description

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Build ID: Camino 2003041205

Reproducible: Always

Steps to reproduce:
1) Print http://www.hut.fi/~hsivonen/test/alpha-print.html

Actual results:
The transparent PNG image is composited on white and then passed to the OS
printing service as a non-transparent bitmap. As a result, the CSS border that
is behind the image is completely covered by the image instead of showing through.

Expected results:
Since the print service of OS X can handle transparency, expected the bitmap to
be handed with the alpha channel to the print service so that the outcome would
more closely resemble the on-screen rendering.

Comment 1

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Attachment: Actual results from Camino

Comment 2

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Attachment: Expected results from Safari

Comment 3

[Boris Zbarsky [:bzbarsky]]

*** This bug has been marked as a duplicate of 141656 ***

Comment 4

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Reopening. Bug 141656 is about partial workarounds for printing services that
can't do full alpha. This is about passing the full alpha to a printing service
that can take it.

Comment 5

[Roland Mainz]

Henri Sivonen wrote:
> Reopening. Bug 141656 is about partial workarounds for printing services that
> can't do full alpha. This is about passing the full alpha to a printing 
> service that can take it.

Does MacOSX support an alpha channel for printers ?!

Comment 6

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

> Does MacOSX support an alpha channel for printers ?!

Yes (since Mac OS X 10.2.something). The app can use the PDF 1.4 imaging model
including transparency.

Comment 7

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Things to do in
http://lxr.mozilla.org/seamonkey/source/gfx/src/mac/nsImageMac.cpp#338

1) Interleave the color data and the mask into an RGBA buffer.
2) Make a CGImageRef out of the buffer.
3) Get a Quartz graphics context for the grafport using QDBeginCGContext.
4) Figure out the coordinate system transformations.
5) Draw the image using CGContextDrawImage.
6) Re-enable QuickDraw using QDEndCGContext.

Comment 8

[Kathleen :Brade]

*** Bug 137114 has been marked as a duplicate of this bug. ***

Comment 9

[Simon Fraser [no longer active]]

Note that printing of transparent PNGs is vital for printing directions on Google Maps.

Comment 10

[Martijn Wargers (dead)]

This is also an issue in current trunk and branch builds on windows.

Comment 11

[Mike Kleshov]

This bug is in Firefox 3 RC1.
The link in the original report is dead. For an example of a web page with a transparent image, see here:
http://www.w3.org/Graphics/PNG/inline-alpha.html
(Hopefully, this link lives longer)
It is surprising that this bug is receiving so little attention. By the way, Opera prints web pages with transparent images correctly.

Comment 12

[Henri Sivonen (:hsivonen) (not reading bugmail until 2026-07-27)]

Fixing the test case link.