Path: csiph.com!fu-berlin.de!usenet.stanford.edu!not-for-mail From: Fred Kiefer Newsgroups: gnu.gnustep.bug Subject: [bug #57335] PNG writing support appears to be broken Date: Sun, 1 Dec 2019 17:00:10 -0500 (EST) Lines: 36 Approved: bug-gnustep@gnu.org Message-ID: References: <20191201-185428.sv47215.42504@savannah.gnu.org> <20191201-220010.sv431.4631@savannah.gnu.org> NNTP-Posting-Host: lists.gnu.org Mime-Version: 1.0 Content-Type: text/plain;charset=UTF-8 X-Trace: usenet.stanford.edu 1575237616 18505 209.51.188.17 (1 Dec 2019 22:00:16 GMT) X-Complaints-To: action@cs.stanford.edu To: Fred Kiefer , Yavor Doganov , bug-gnustep@gnu.org Envelope-to: bug-gnustep@gnu.org X-PHP-Originating-Script: 1001:sendmail.php X-Savane-Server: savannah.gnu.org:443 [2001:470:142:5::79] X-Savane-Project: gnustep X-Savane-Tracker: bugs X-Savane-Item-ID: 57335 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0 X-Apparently-From: 2001:16b8:2bed:400:9b7e:1f97:b2d7:d5d3 (Savane authenticated user FredKiefer) In-Reply-To: <20191201-185428.sv47215.42504@savannah.gnu.org> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.51.188.79 X-BeenThere: bug-gnustep@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Bug reports for the GNUstep programming environment List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Mailman-Original-Message-ID: <20191201-220010.sv431.4631@savannah.gnu.org> X-Mailman-Original-References: <20191201-185428.sv47215.42504@savannah.gnu.org> Xref: csiph.com gnu.gnustep.bug:4359 Update of bug #57335 (project gnustep): Status: None => Confirmed Assigned to: None => FredKiefer _______________________________________________________ Follow-up Comment #1: The test code you provides tries to convert a tiff file into a PNG image. This should be possible with GNUstep. I tried to convert the GNUstep logo from tiff to PNG and ended up with an image where the white bits where shown as black. Is this the bug you are reporting? What the code here does is to follow the PNG specification. PNG stores values with non pre-multiplied alpha. GNUstep internally uses pre-multiplied alpha as this allows for faster drawing. When exporting to PNG we need to make sure we output the data non pre-multiplied and this code here tries to do the conversion. What you did is switch off this conversion. And for simple data where alpha is either 1 or 0 this results in correct images. But this of course does not solve the issue why the conversion is wrong. Sorry, I will need some more time to look into this. _______________________________________________________ Reply to this item at: _______________________________________________ Message sent via Savannah https://savannah.gnu.org/