From owner-png-implement@dworkin.wustl.edu Tue Oct 1 15:12:58 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id PAA17844 for ; Tue, 1 Oct 1996 15:12:57 -0500 (CDT) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id PAA08495 for png-implement-outgoing; Tue, 1 Oct 1996 15:12:20 -0500 Received: from enel.ucalgary.ca ([136.159.100.11]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id PAA08489 for ; Tue, 1 Oct 1996 15:12:15 -0500 Received: from munet-d.enel by enel.ucalgary.ca (SMI-8.6/ENEL-5) id OAA20667; Tue, 1 Oct 1996 14:11:26 -0600 From: adilger@enel.ucalgary.ca (Andreas Dilger) Message-Id: <199610012011.OAA20667@enel.ucalgary.ca> Subject: Re: PNG vs GIF Image sizes (again) To: gifconverter@kamit.com Date: Tue, 1 Oct 1996 14:11:25 -0600 (MDT) Cc: png-implement@dworkin.wustl.edu (PNG Implementation) In-Reply-To: from "Kevin A. Mitchell" at Sep 29, 96 10:17:59 am X-Mailer: ELM [version 2.4 PL23] Content-Type: text Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List Kevin writes: > 1) Adding comments: I have some translation tables for ISO 8859-1 to and > from Macintosh. Since GIFConverter only has user interface and internal > representation for a monolithic comment, I plan to aggregate comments with > keywords on read, and output a single Comment: comment when writing. I do > plan to enhance the internal representation once I can hook up a decent > user interface, hopefully something like the way Eudora handles mail > headers. I was faced with the same problems under XV for comment handling - it only supports a single comment for an image. Since I'm not in charge of the XV code (I just worked on Alexander's XV patch), I didn't want to go through the effort of changing the whole code to support multiple comments per image. To get around this limitation, I had XV add some extra delimiters between the keyword and comment text, and then I parse the keywords out afterwards. While this only works when reading and writing PNG files, this is really the only time it matters, since in XV the user can't change the comment text anyways. In XV-PNG comments, a keyword starts at the beginning of a line, followed by two colons, and then the comment. I figure it is unlikely enough that there is a double colon in a comment to do it this way, and yet it still looks OK when displayed. For the small chance that it will mis-parse a keyword/comment, I think it worthwhile to preserve the unique PNG keyword/ comment pairs. Cheers, Andreas. -- Andreas Dilger University of Calgary \"If a man ate a pound of pasta and (403) 220-8792 Micronet Research Group \ a pound of antipasto, would they Dept of Electrical & Computer Engineering \ cancel out, leaving him still http://www-mddsp.enel.ucalgary.ca/People/adilger/ hungry?" -- Dogbert ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Tue Oct 8 14:20:55 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id OAA15566 for ; Tue, 8 Oct 1996 14:20:54 -0500 (CDT) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id OAA21833 for png-implement-outgoing; Tue, 8 Oct 1996 14:21:22 -0500 Received: from mail.uni-muenster.de (MAIL.UNI-MUENSTER.DE [128.176.6.47]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id OAA21827 for ; Tue, 8 Oct 1996 14:21:13 -0500 Received: from PPPE095.UNI-MUENSTER.DE (PPPE095.UNI-MUENSTER.DE [128.176.20.101]) by mail.uni-muenster.de (8.7.5/8.7.5) with SMTP id VAA87394 for ; Tue, 8 Oct 1996 21:19:53 +0200 Date: Tue, 8 Oct 1996 21:19:53 +0200 Message-Id: <199610081919.VAA87394@mail.uni-muenster.de> X-Sender: tilman@machno.hbi-stuttgart.de X-Mailer: Windows Eudora Light Version 1.5.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: png-implement@dworkin.wustl.edu From: Tilman Meierfrankenfeld Subject: PNG Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List Hello ! I would like PNG for a WINDOWS-program. Do you know, if any quantisations-tools for PNG exist? How can I create a palete? Sincerly, Tilman Meierfrankenfeld -------------------------------------------------------------- * Tilman Meierfrankenfeld Phone/Fax:+ 49 251 316983 * * Pleistermuehlenweg 109 e-mail: meierfr@uni-muenster.de * * 48155 Muenster * * Germany * -------------------------------------------------------------- ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Wed Oct 9 06:37:55 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id GAA05085 for ; Wed, 9 Oct 1996 06:37:54 -0500 (CDT) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id GAA05845 for png-implement-outgoing; Wed, 9 Oct 1996 06:38:51 -0500 Received: from grommit.inria.fr (grommit.inria.fr [138.96.48.84]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id GAA05840 for ; Wed, 9 Oct 1996 06:38:47 -0500 Received: by grommit.inria.fr (8.7.6/8.6.12) id NAA05289 for png-implement@dworkin.wustl.edu; Wed, 9 Oct 1996 13:37:32 +0200 (DST) Date: Wed, 9 Oct 1996 13:37:32 +0200 (DST) From: Chris Lilley Message-Id: <9610091337.ZM5287@grommit.inria.fr> In-Reply-To: Tilman Meierfrankenfeld "PNG" (Oct 8, 9:19pm) References: <199610081919.VAA87394@mail.uni-muenster.de> X-Mailer: Z-Mail (3.2.2 10apr95 MediaMail) To: PNG Implementation List Subject: Re: PNG Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List On Oct 8, 9:19pm, Tilman Meierfrankenfeld wrote: > I would like PNG for a WINDOWS-program. Do you know, if any > quantisations-tools for PNG exist? How can I create a palete? There are tools that will read a truecolor PNG, change mode to indexed, and write an indexed PNG. Debablizer, XRes2.0, and Photoshop 4.0 spring to mind (is Debablelizer windows too, or Mac only?) -also PixFolio I believe. It is also possible to convert to an intermediate processing format, quantize with your method of choice, and convert back to PNG. That's what I do on Unix, using the netpbm toolkit. This assumes that the original PNG is truecolor RGB. RGBA or tRNS PNGs converted to an indexed PNG with a tRNS chunk - I don't know which of the current tools can do that. Anyone else know? -- Chris Lilley, W3C [ http://www.w3.org/ ] Graphics and Fonts Guy The World Wide Web Consortium http://www.w3.org/people/chris/ INRIA, Projet W3C chris@w3.org 2004 Rt des Lucioles / BP 93 +33 93 65 79 87 06902 Sophia Antipolis Cedex, France ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Tue Oct 15 11:38:13 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id LAA03140 for ; Tue, 15 Oct 1996 11:38:12 -0500 (CDT) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id LAA06518 for png-implement-outgoing; Tue, 15 Oct 1996 11:39:31 -0500 Received: from mail-server.dk-online.dk (mail-server.dk-online.dk [194.234.20.2]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id LAA06507 for ; Tue, 15 Oct 1996 11:39:27 -0500 Message-Id: <199610151639.LAA06507@dworkin.wustl.edu> Received: from ppp218.dk-online.dk [194.234.16.218] (HELO KimThryse.dk-online.dk) by mail-server.dk-online.dk (MAILbus F1.0/1.0 BL11 listener) id 0000_007b_3263_bdb6_da6a; Tue, 15 Oct 1996 18:37:10 +0200 From: "Thrysoe" To: Subject: *FREE* Pascal implemtation Date: Tue, 15 Oct 1996 18:34:14 +0100 X-MSMail-Priority: Normal X-Priority: 3 X-Mailer: Microsoft Internet Mail 4.70.1155 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List Does anyone know of a good, accesible implementation in Pascal? It has to be free of charge and royalties, since I do not have "space" for operating with thoose parameters. Cheers! (...and do not hesitate to CC me) ------------------- .sig seperator ------------------ qabi Dennis Thrysøe Dennis Thrysøe TeamTest Coordinator ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Thu Oct 17 09:30:50 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id JAA27016 for ; Thu, 17 Oct 1996 09:30:47 -0500 (CDT) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id JAA14216 for png-implement-outgoing; Thu, 17 Oct 1996 09:31:27 -0500 Received: from obelix.hrz.tu-chemnitz.de (obelix.hrz.tu-chemnitz.de [134.109.132.55]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id JAA14210 for ; Thu, 17 Oct 1996 09:31:06 -0500 Received: from physikus.physik.tu-chemnitz.de by obelix.hrz.tu-chemnitz.de with Local SMTP (PP) id <10205-0@obelix.hrz.tu-chemnitz.de>; Thu, 17 Oct 1996 16:27:22 +0200 Received: by physikus.physik.tu-chemnitz.de (4.1/SMI-4.1) id AA26448; Thu, 17 Oct 96 16:27:30 +0200 Date: Thu, 17 Oct 1996 16:27:29 +0200 (MET DST) From: Jacques Nomssi Nzali To: PNG Implementation List Subject: Re: *FREE* Pascal implemtation In-Reply-To: <199610151639.LAA06507@dworkin.wustl.edu> Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List On Tue, 15 Oct 1996, Thrysoe wrote: > Does anyone know of a good, accesible implementation in Pascal?=20 > It has to be free of charge and royalties, since I do not have "space"=20 > for operating with thoose parameters. >=20 > Cheers! > (...and do not hesitate to CC me) > Dennis Thrys=F8e , Ask Bob Cousins . He has done some work on a Pascal version of zlib. Jacques Nomssi Nzali [kn&n DES] NVIEW ftp server ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Mon Oct 28 16:17:11 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id QAA15143 for ; Mon, 28 Oct 1996 16:17:10 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id QAA14829 for png-implement-outgoing; Mon, 28 Oct 1996 16:19:39 -0600 Received: from fm3.facility.pipex.com (fm3.facility.pipex.com [194.131.104.13]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id QAA14824 for ; Mon, 28 Oct 1996 16:19:35 -0600 Received: from 193.130.249.167 (aj167.du.pipex.com) by fm3.facility.pipex.com (5.x/PIPEX simple 1.26) id AA21380; Mon, 28 Oct 1996 21:17:01 GMT Message-Id: <9610282117.AA21380@fm3.facility.pipex.com> Mime-Version: 1.0 From: ttehtann@argonet.co.uk (Tom Tanner) To: adilger@enel.ucalgary.ca, png-implement@dworkin.wustl.edu Date: Mon, 28 Oct 96 22:14:02 X-Mailer: VTi Internet Email reader 1.08 : aa Subject: libpng 0.89 Content-Type: text/plain Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List A couple of problems / thoughts while playing around with background colours using the HELL picture (which has a nice fade round the edge): 1/ Selecting a background with any of the R, G or B components not 0 or 100% causes frightful moire patterning. Is this just tough, or can we think of a better algorithm (or is it my Acorn, using 16 bit colour downgraded to 8 bits?) 2/ There are definitely bugs in the handling of background gammas: a/ Any attempt to use gamma correction causes the background (if composited) to come out a foul grey tint, except where the picture is fully transparent, where the code does a quick optimisation, which hides the problem completely (try taking the 'if (a == 0)' stuff out in png_do_background). b/ Using PNG_BACKGROUND_GAMMA_UNKNOWN with png_set_background causes strange things to happen, as no gamma tables are set up, but they are still used. If I am wittering, please let me know, but I'm fairly sure this isn't me. Thanks very much Tom -- Thos -- T. R. Tanner email: ttehtann@argonet.co.uk ZFC: A Alien %0100 : In CyberSpace, no one can hear you scream ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Tue Oct 29 01:20:17 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id BAA18740 for ; Tue, 29 Oct 1996 01:20:16 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id BAA22555 for png-implement-outgoing; Tue, 29 Oct 1996 01:23:08 -0600 Received: from iagu.on.net (iagu.on.net [192.83.231.86]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id BAA22549 for ; Tue, 29 Oct 1996 01:23:03 -0600 Received: from localhost [127.0.0.1] by iagu.on.net (8.6.9/AndrewR-940528) with SMTP id RAA19699 return ; Tue, 29 Oct 1996 17:49:50 +1030 Message-Id: <199610290719.RAA19699@iagu.on.net> From: jsam@iagu.on.net (Sam Bushell) To: PNG Implementation List Cc: ttehtann@argonet.co.uk Subject: Re: libpng 0.89 In-reply-to: Your message of "Mon, 28 Oct 96 22:14:02 -0000." <9610282117.AA21380@fm3.facility.pipex.com> Date: Tue, 29 Oct 96 17:49:49 +1030 X-Mts: smtp Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List G'day, Tom. Are you using libpng 0.89 or 0.89c? What are your platform and compiler? (Someone else on the list may have experience with a similar environment.) ttehtann@argonet.co.uk writes: > A couple of problems / thoughts while playing around with background colours > using the HELL picture (which has a nice fade round the edge): > > 1/ Selecting a background with any of the R, G or B components not 0 or 100% > causes frightful moire patterning. Is this just tough, or can we think of a > better algorithm (or is it my Acorn, using 16 bit colour downgraded to 8 bits > ?) Hmmm. I've used backgrounds other than white and black with no such peculiarities. However, I've been using libpng to decompress PNGs to 24-bit RGB colour and then doing dithering externally (ie, not using libpng). Can you be more precise about the kinds of PNGs that exhibit this problem and what point the image is dithered down to 8-bit indexed colour (and to whose palette)? > 2/ There are definitely bugs in the handling of background gammas: > > a/ Any attempt to use gamma correction causes the background (if composited) > to > come out a foul grey tint, except where the picture is fully transparent, whe > re > the code does a quick optimisation, which hides the problem completely (try > taking the 'if (a == 0)' stuff out in png_do_background). I have used gamma correction and composited backgrounds without encountering foul grey tints. I tend to steer away from foul grey backgrounds, however... > b/ Using PNG_BACKGROUND_GAMMA_UNKNOWN with png_set_background causes strange > things to happen, as no gamma tables are set up, but they are still used. Hmmm. I'm not sure I can field this thoroughly. However, I'm not sure that it's appropriate to specify PNG_BACKGROUND_GAMMA_UNKNOWN to png_set_background. You should have some gamma in mind for the colour you're specifying; either it should match that in the file or that on the screen, or something else? > T. R. Tanner email: ttehtann@argonet.co.uk ZFC: A jsam ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Tue Oct 29 08:41:01 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id IAA22204 for ; Tue, 29 Oct 1996 08:41:01 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id IAA26496 for png-implement-outgoing; Tue, 29 Oct 1996 08:43:45 -0600 Received: from uu.psi.com (uu.psi.com [136.161.128.3]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id IAA26490 for ; Tue, 29 Oct 1996 08:43:41 -0600 Received: from mentalix.com by uu.psi.com (5.65b/4.0.061193-PSI/PSINet) via UUCP; id AA11094 for ; Tue, 29 Oct 96 09:31:45 -0500 From: cain@mentalix.com (Celeste Cain) Received: by mentalix.com (940816.SGI.8.6.9/3.2.083191-Mentalix) id OAA01857; Tue, 29 Oct 1996 14:28:49 GMT Message-Id: <199610291428.OAA01857@mentalix.com> Subject: Netscape Plug-in? To: png-implement@dworkin.wustl.edu Date: Tue, 29 Oct 1996 08:28:48 -0600 (CST) In-Reply-To: <9610282117.AA21380@fm3.facility.pipex.com> from "Tom Tanner" at Oct 28, 96 10:14:02 pm X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List Sorry if this is redundant, but I was wondering how many Netscape plug-ins there were at this point and what they required. Are there any known UNIX plug-ins? Thanks, Celeste ~~~~~~~~~~~~~~~~~~~~~~~~~~ Celeste Cain Mentalix, Inc. 1700 Alma Drive Suite 110 Plano, TX 75075 email : cain@mentalix.com phone : (972) 423-9377 x33 WWW: http://www.pfx.com ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Tue Oct 29 09:30:22 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id JAA22678 for ; Tue, 29 Oct 1996 09:30:21 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id JAA27152 for png-implement-outgoing; Tue, 29 Oct 1996 09:33:27 -0600 Received: from haven.uchicago.edu (haven.uchicago.edu [128.135.12.3]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id JAA27147 for ; Tue, 29 Oct 1996 09:33:24 -0600 Received: from kimbark.uchicago.edu (kimbark.uchicago.edu [128.135.12.52]) by haven.uchicago.edu (8.7.5/8.7.3) with ESMTP id JAA13586 for ; Tue, 29 Oct 1996 09:28:59 -0600 (CST) Received: (from roe2@localhost) by kimbark.uchicago.edu (8.7.5/8.7.3) id JAA16922; Tue, 29 Oct 1996 09:30:10 -0600 (CST) Date: Tue, 29 Oct 1996 09:30:10 -0600 (CST) Message-Id: <199610291530.JAA16922@kimbark.uchicago.edu> To: png-implement@dworkin.wustl.edu Subject: Re: Netscape Plug-in? From: Cave Newt Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List >Sorry if this is redundant, but I was wondering how many >Netscape plug-ins there were at this point and what they >required. Are there any known UNIX plug-ins? See http://quest.jpl.nasa.gov/PNG/pngapbr.html . Yes. Greg ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Wed Oct 30 16:57:59 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id QAA18123 for ; Wed, 30 Oct 1996 16:57:58 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id RAA23509 for png-implement-outgoing; Wed, 30 Oct 1996 17:00:39 -0600 Received: from fm3.facility.pipex.com (fm3.facility.pipex.com [194.131.104.13]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id RAA23503 for ; Wed, 30 Oct 1996 17:00:31 -0600 Received: from ai097.du.pipex.com by fm3.facility.pipex.com (5.x/PIPEX simple 1.26) id AB01278; Wed, 30 Oct 1996 21:58:18 GMT Message-Id: <9610302158.AB01278@fm3.facility.pipex.com> Mime-Version: 1.0 From: ttehtann@argonet.co.uk (Tom Tanner) To: png-implement@dworkin.wustl.edu Date: Wed, 30 Oct 96 21:41:50 X-Mailer: VTi Internet Email reader 1.08 : aa Subject: Re: libpng 0.89 Content-Type: text/plain Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List On , jsam@iagu.on.net wrote: > >G'day, Tom. > >Are you using libpng 0.89 or 0.89c? 0.89c >What are your platform and compiler? (Someone else on the list may have > experience with a similar environment.) Acorn RiscOS, Acorn C Compiler > >ttehtann@argonet.co.uk writes: >> A couple of problems / thoughts while playing around with background colours >> using the HELL picture (which has a nice fade round the edge): >> >> 1/ Selecting a background with any of the R, G or B components not 0 or 100% >> causes frightful moire patterning. Is this just tough, or can we think of a >> better algorithm (or is it my Acorn, using 16 bit colour downgraded to 8 >> bits ?) > >Hmmm. I've used backgrounds other than white and black with no such >peculiarities. However, I've been using libpng to decompress PNGs to >24-bit RGB colour and then doing dithering externally (ie, not using >libpng). > >Can you be more precise about the kinds of PNGs that exhibit this >problem and what point the image is dithered down to 8-bit indexed >colour (and to whose palette)? "Hell" (Peppers) shows this effect beatifully. > >> 2/ There are definitely bugs in the handling of background gammas: >> >> a/ Any attempt to use gamma correction causes the background (if >> composited) to come out a foul grey tint, except where the picture is fully >> transparent, where the code does a quick optimisation, which hides the >> problem completely (try taking the 'if (a == 0)' stuff out in >> png_do_background). > >I have used gamma correction and composited backgrounds without >encountering foul grey tints. I tend to steer away from foul grey >backgrounds, however... It's foul grey with any colour background. However.. Further investigation indicates that what is happening is that there is confusion (either on my half or the libraries) about how you specify the background. I have it specified as a 16 bit RGB triplet (as per png_color16). However, if you have selected 8 bit stripping, the background is not stripped. Result: Both the above effects happen! OK, Question: HOW do we specify the background?!? I would have thought that all backgrounds should be specified as 16 bit, and the library cope if necessary with doing any necessary conversions. Certainly, if a background is going to be supplied with a (3*)16 bit RGB picture, it should do this, and apparently does not. I am however somewhat worried that fixing this bug (which requires just a couple of lines in png_init_read_transformations (he said with great optimism)) will break existing code - how many people with (3*)8 bit RGB displays give a similarly defined background colour? > >> b/ Using PNG_BACKGROUND_GAMMA_UNKNOWN with png_set_background causes strange >> things to happen, as no gamma tables are set up, but they are still used. > >Hmmm. I'm not sure I can field this thoroughly. However, I'm not >sure that it's appropriate to specify PNG_BACKGROUND_GAMMA_UNKNOWN to >png_set_background. You should have some gamma in mind for the colour >you're specifying; either it should match that in the file or that on >the screen, or something else? I'm pretty sure it's valid - there is a test for it where the other background tests are tested. But I don't know what it's meant to do. Should it 1) Gamma correct the picture and then compose with the background 2) Do no gamma correction at all 3) Compose the pixel with the background & then gamma correct 4) None of the above? -- Thos -- T. R. Tanner email: ttehtann@argonet.co.uk ZFC: A Alien %0100 : In CyberSpace, no one can hear you scream ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Wed Oct 30 19:53:10 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id TAA19438 for ; Wed, 30 Oct 1996 19:53:09 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id TAA25554 for png-implement-outgoing; Wed, 30 Oct 1996 19:56:10 -0600 Received: from iagu.on.net (iagu.on.net [192.83.231.86]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with ESMTP id TAA25549 for ; Wed, 30 Oct 1996 19:56:04 -0600 Received: from localhost [127.0.0.1] by iagu.on.net (8.6.9/AndrewR-940528) with SMTP id MAA02446 for png-implement@dworkin.wustl.edu return ; Thu, 31 Oct 1996 12:22:36 +1030 Message-Id: <199610310152.MAA02446@iagu.on.net> From: jsam@iagu.on.net (Sam Bushell) To: PNG Implementation List Subject: Re: libpng 0.89 In-reply-to: Your message of "Wed, 30 Oct 96 21:41:50." <9610302158.AB01278@fm3.facility.pipex.com> Date: Thu, 31 Oct 96 12:22:35 +1030 X-Mts: smtp Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List > >Can you be more precise about the kinds of PNGs that exhibit this > >problem and what point the image is dithered down to 8-bit indexed > >colour (and to whose palette)? > > "Hell" (Peppers) shows this effect beatifully. In your program, at what point the image is dithered down to 8-bit indexed colour (and to whose palette)? > However.. Further investigation indicates that what is happening is that ther > e > is confusion (either on my half or the libraries) about how you specify the > background. I have it specified as a 16 bit RGB triplet (as per png_color16). > However, if you have selected 8 bit stripping, the background is not stripped > . > Result: Both the above effects happen! > > OK, Question: HOW do we specify the background?!? I would have thought that a > ll > backgrounds should be specified as 16 bit, and the library cope if necessary > with doing any necessary conversions. Certainly, if a background is going to > be > supplied with a (3*)16 bit RGB picture, it should do this, and apparently doe > s > not. Ah, yes, I thought that once. I believe the background colour must match the file format. I use this: png_color_16 my_background_8 = { 0, 0xff,0xff,0xff, 0xff }; png_color_16 my_background_16 = { 0, 0xffff,0xffff,0xffff, 0xffff }; if( imageHasAlphaChannelOrTransparency ) { if (info_ptr->valid & PNG_INFO_bKGD) png_set_background( png_ptr, &(info_ptr->background), PNG_BACKGROUND_GAMMA_FILE, 1, 1.0 ); else png_set_background( png_ptr, ( 16 == info_ptr->bit_depth ) ? &my_background_16 : &my_background_8, PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0 ); } (But you should note that I always expand images to 8-bit per channel RGB. When expanding to 8-bit indexed colour, I suspect you have to specify a pixel value instead. I can't suggest anything better than reading the source, I'm afraid.) > >> b/ Using PNG_BACKGROUND_GAMMA_UNKNOWN with png_set_background causes stran > ge > >> things to happen, as no gamma tables are set up, but they are still used. > > > >Hmmm. I'm not sure I can field this thoroughly. However, I'm not > >sure that it's appropriate to specify PNG_BACKGROUND_GAMMA_UNKNOWN to > >png_set_background. You should have some gamma in mind for the colour > >you're specifying; either it should match that in the file or that on > >the screen, or something else? > > I'm pretty sure it's valid - there is a test for it where the other backgroun > d > tests are tested. But I don't know what it's meant to do. Should it I suspect it's a loose piece of logic, that png_set_background assumes you are specifying something other than PNG_BACKGROUND_GAMMA_UNKNOWN (but doesn't check, and it probably should.). I think the simple answer is "don't use PNG_BACKGROUND_GAMMA_UNKNOWN with png_set_background". :-) jsam ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body. From owner-png-implement@dworkin.wustl.edu Thu Oct 31 15:56:59 1996 Received: from dworkin.wustl.edu (dworkin.wustl.edu [128.252.169.2]) by swrinde.nde.swri.edu (8.7.6/8.7.3) with SMTP id PAA01370 for ; Thu, 31 Oct 1996 15:56:58 -0600 (CST) Received: (from daemon@localhost) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) id PAA10183 for png-implement-outgoing; Thu, 31 Oct 1996 15:59:12 -0600 Received: from fm3.facility.pipex.com (fm3.facility.pipex.com [194.131.104.13]) by dworkin.wustl.edu (8.6.10/8.6.6.yuck) with SMTP id PAA10174 for ; Thu, 31 Oct 1996 15:58:55 -0600 Received: from 193.130.248.73 (ai073.du.pipex.com) by fm3.facility.pipex.com (5.x/PIPEX simple 1.26) id AA21398; Thu, 31 Oct 1996 20:56:37 GMT Message-Id: <9610312056.AA21398@fm3.facility.pipex.com> Mime-Version: 1.0 From: ttehtann@argonet.co.uk (Tom Tanner) To: png-implement@dworkin.wustl.edu Date: Thu, 31 Oct 96 21:18:27 X-Mailer: VTi Internet Email reader 1.08 : aa Subject: Re: libpng 0.89 Content-Type: text/plain Sender: owner-png-implement@dworkin.wustl.edu Precedence: bulk Reply-To: PNG Implementation List On , jsam@iagu.on.net wrote: >In your program, at what point the image is dithered down to 8-bit >indexed colour (and to whose palette)? Umm, that's up to libpng... > >> However.. Further investigation indicates that what is happening is that >> there is confusion (either on my half or the libraries) about how you >> specify the background. I have it specified as a 16 bit RGB triplet (as per >> png_color16). >> However, if you have selected 8 bit stripping, the background is not >> stripped. Result: Both the above effects happen! I think I got muddled here - the Hell picture is only 8 bits to start with. >> >> OK, Question: HOW do we specify the background?!? I would have thought that >> all backgrounds should be specified as 16 bit, and the library cope if >> necessary with doing any necessary conversions. Certainly, if a background >> is going to be supplied with a (3*)16 bit RGB picture, it should do this, >> and apparently does not. > >Ah, yes, I thought that once. I believe the background colour must >match the file format. I use this: > > png_color_16 my_background_8 = { 0, 0xff,0xff,0xff, 0xff }; > png_color_16 my_background_16 = { 0, 0xffff,0xffff,0xffff, 0xffff }; > > if( imageHasAlphaChannelOrTransparency ) > { > if (info_ptr->valid & PNG_INFO_bKGD) > png_set_background( png_ptr, &(info_ptr->background), > PNG_BACKGROUND_GAMMA_FILE, 1, 1.0 ); > else > png_set_background( > png_ptr, > ( 16 == info_ptr->bit_depth ) ? > &my_background_16 : &my_background_8, > PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0 ); > } > >(But you should note that I always expand images to 8-bit per channel >RGB. When expanding to 8-bit indexed colour, I suspect you have to >specify a pixel value instead. I can't suggest anything better than >reading the source, I'm afraid.) Having just re-re-read the spec, I got it wrong. Cringe :-(. I must have been tired last night. Thanks for the help. -- Thos -- T. R. Tanner email: ttehtann@argonet.co.uk ZFC: A Alien %0100 : In CyberSpace, no one can hear you scream ------------------------------------------------------------ To find out more about the mailing list server, send mail to png-implement-request@dworkin.wustl.edu with the word "help" (and nothing else) in the message body.