Talk:PNG/Archive 1

message: (Your Standard Anti-Troll-War Discl: I hate working with IE 6/XHTML/CSS2-combination and I can only hope that IE 7 will be an improvement, etc. But.)
The Web browser support for PNG section contains the following:
Internet Explorer 7 has limited support for PNG transparency. It displays the wrong colors within images and thus does not have 100% compatibility.
Is this a piece of fact or simply Criticism of Internet Explorer? ;) I think there are at least two totally different things mixed here into one line:
First, IE 7 has a new PNG alpha channel engine . Is it limited? If yes, then what are the limits? Facts, please.
: I am not aware of any limitations or errors; it appears to pass all of my test cases. But note that the combination of alpha and gamma is quite tricky, and I have not tested that. (There would seem to be little purpose to it at this point; see below.) -- Roelofs 08:38, 22 December 2006 (UTC)
replies: text: No, IE7's gamma support is demonstrably wrong. The argument goes like this: HTML colors are recommended to be in the sRGB color space. CSS colors are required to be sRGB. (sRGB is defined to have gamma 2.2.) Legacy web-page designs used unlabelled GIFs and JPEGs in combination with HTML and CSS colors and matched them by eye; ergo, unlabelled images, including PNGs, should similarly be considered sRGB for the sake of backward compatibility (which virtually all browser-vendors deeply care about). Immediate corollary: any browser that gamma-corrects unlabelled PNGs in a manner different from PNGs containing an sRGB chunk, an sRGB iCCP chunk, or a gAMA 1/2.2 chunk is in error.  Any browser that gamma-corrects the latter three categories of PNGs in a manner different from HTML and/or CSS colors is in error. IE7 treats PNGs with gAMA chunks inconsistently with its treatment of HTML and CSS colors; ergo, it's broken. (It also doesn't support color correction at all.)  -- Roelofs 08:38, 22 December 2006 (UTC)

text: That works only on systems approximating sRGB (which, admittedly, is most of them these days).  Doing so on a Mac (at least, older models), an SGI workstation, or a NeXT cube would probably be a mistake. -- Roelofs 08:38, 22 December 2006 (UTC)

text: On the other hand, libpng was written and is maintained by those who wrote the specification; that is not true of MSIE. ;-) In any case, I modified the wording in this section earlier this evening, and I included a link to my screenshots/analysis page. -- Roelofs 08:38, 22 December 2006 (UTC)
thread_title: Internet Explorer 7

message: Might need to disambiguate this from Papua New Guinea at some point —Mulad, May 29, 2003
:seems someone did that a while ago now. Plugwash 22:51, 5 August 2005 (UTC)
thread_title: Papua New Guinea

message: Does anyone know how to tell whether two PNG images are the same image, i.e. all pixels identical?  If there's no transparency, one can convert to PNM and use pnmpsnr.  But in general?  dbenbenn | talk 21:37, 3 Jun 2005 (UTC)
replies: text: Bah.  Apparently I'll have to learn the PNG format and write my own program.  dbenbenn | talk 21:40, 18 Jun 2005 (UTC)
replies: text: i've written a png writer but i've never attempted a reader, sorry. Plugwash 22:02, 18 Jun 2005 (UTC)
replies: text: Can't you just convert to RGB or RGBA with ImageMagick's convert program, then do diff --brief on the result? Ojw 00:31, 15 August 2005 (UTC)
thread_title:  Compare two PNGs 

message: Does anyone have any idea what all gratis software are available to write metadata into a PNG file? =Nichalp «Talk»= July 4, 2005 10:20 (UTC)
:GIMP 2.2 has, I am told, a full metadata editor plugin. I'm testing it out at this point; I'll follow up here once I've figured it out. grendel|khan July 4, 2005 19:09 (UTC)
::Okay, I can't seem to find it, if it's in there. Must not be included in the latest Windows version. There's an EXIF browser you can get for it, or a much, much more full-featured one which happens not to be fully implemented yet, but is in the GIMP CVS and scheduled for release along with 2.3.0, it seems. grendel|khan July 4, 2005 20:03 (UTC)
:Here's something to read metadata... grendel|khan July 4, 2005 19:25 (UTC)
:Okay, I got it for sure this time. Use PNGCRUSH; it reads and writes tEXt, iTXt, zTXt and pretty much every other kind of chunk. Use pngcrush -v -n file.png to get the metadata. grendel|khan July 4, 2005 20:09 (UTC)
::Thanks, but I couldn't fully run the win32 version I downloaded. I copied it into the system32 folder, but 'pngcrush' seemed to be a non existant file. :( =Nichalp «Talk»= July 9, 2005 06:05 (UTC)
::I've used pngcrush (on linux and windows) and it works great, both for reading and writing metadata.  If you run it without any arguments, it will tell you the syntax.  For example, to insert an uncompressed itxt chunk after the idat data you would use pngcrush -itxt a your_keyword_here you_textual_data_here input_file.png outputfile.png  eck
:Hey people, this is forgetting about TweakPNG from Jason Summers. Not only it can display all metadata contained in PNG files, but it can also edit them and add new text chunks, and really easily. Dioxaz 18:57, 21 October 2005 (UTC)
thread_title:  Metadata 

message: : "but it is often spelt out possibilly to avoid confusion with the internet tool ping"
What is the phrase trying to say? (i.e. could someone reword it to make sense, as I'm not 100% sure what the meaning is supposed to be)
-- Matthew0028 13:02, 14 August 2005 (UTC)
replies: text: It's trying to say that it's often spelt out: pee en jee. --Zundark 18:24, 14 August 2005 (UTC)
replies: text: I think it means: "It's often pronounced 'P. N. G.'. One reason for so doing is that the word "PNG (pronounced 'ping')" might be mistaken for the word "ping" (which is a UNIX command/program/protocol, among other things)".
Just noticed: you might want to put a note into ping (disambiguation) if people will be calling it that, and someone looks up the Ping graphics format on wikipedia to see what it is... Ojw 18:38, 14 August 2005 (UTC)
thread_title: Intro paragraph

message: Of what relevance is the Windows Picture and Fax Viewer link to this article?  
If we linked instead to Comparison of image viewers, that would probably give a good description of which image viewers support PNG. Ojw 21:19, 17 September 2005 (UTC)
replies: text: * No big deal, but since it inherent to Windows XP, it is one of the widest used viewers capable of displaying PNG images.Phil talk 21:53, 17 September 2005 (UTC)
thread_title: New 'see also' links

message: Someone just changed all instances of "colour" to "color", marking it as a "minor" change.  However, wikipedia style seems to be that articles should be left in the language (US/UK/CA) that they were originally written in, rather than changing things just for the sake of making the article americanized.  
"If an article is predominantly written in one type of English, aim to conform to that type rather than provoking conflict by changing to another.". 
Ojw 20:19, 21 September 2005 (UTC)
thread_title: Colour/color

message: This article is pretty obviously pro-PNG (and also a nice example of Wikipedia being "the encyclopedia Slashdot built").  Could you guys try to tone down the cheerleading a bit?  Both "Comparison" sections do not belong here at all, since any comparison requires personal (i.e. POV)  interpretation and constitutes original research by the contributors.  Neither are appropriate in any encyclopedia, including Wikipedia. —Preceding unsigned comment added by 68.169.62.96 (talk • contribs) 18:48, 2005 December 28
:Have to disagree there - the choice of different formats for different types of image is not POV - it is well known that JPEG is better for photos (which the comparison STATES and is not therefore PNG cheerleading as you suggest) since it was designed for that purpose, and GIF is better for 'graphical' images (ie drawings rather than photos) - and since PNG is intended as a replacement for GIF it stands to reason that PNG would be better than JPEG for the same types of image that GIF is better than JPEG Cynical 23:09, 30 December 2005 (UTC)
replies: text: I'm sorry, but I can see nothing untrue in the small comparison section. Nor do I see any POV, as it is limited to several facts. The JPEG comparison, while much more verbose is quite true as well. JPEG does suffer from those problems and PNG is unsuited for photography or very high resolution type images. Furthermore your opening statement, containing what looks like an adversarial statement, only serves to invite further mud slinging. Please keep criticisms constructive. Dread Lord CyberSkull ✎☠ 07:37, 31 December 2005 (UTC)
replies: text: Agreed: the section as it stands is written in a fair, factual, and neutral way. I'm removing the POV tag. —Lowellian (reply) 15:29, 1 January 2006 (UTC)
thread_title:  POV tagged 

message: any sources for this claim or is it just heresay. if the latter then its getting reverted. Plugwash 22:50, 6 January 2006 (UTC)
thread_title:  "pngs not gif" 

message: I have found that when using some PNG images, when they are shown at a lower size in an article, the automatically generated lower-sized version is much larger in filesize. This certainly happens with :Image:TerraNovabox.png. The image is 28kb, and has a resolution of 259x301 pixels. When shown in the Terra Nova: SFC article at 250px, the resulting file is 119kb, over 4 times the original filesize. As such, I showed it at the original size in the article (9 extra pixels in width doesn't really affect infobox) Why does this happen? If it helps, I'm running IE 6 (though this seems a server-side issue), and I converted the image from GIF to PNG in Paint Shop Pro 7. I have not put the file through any optimisers.--Drat (Talk) 02:17, 17 January 2006 (UTC)
replies: text: Imagemagick upconverts the image to RGB before doing any scaling. unfortunately it doesn't have any system built in to decicide if it should convert back to 256 color or not so the result is that all scaled images are RGB color. Also the very process of scaling can introduce a flood of extra color transisitions round edges that the compression system used in PNG doesn't like. Plugwash 02:56, 17 January 2006 (UTC)
replies: text: Very interesting, thanks. Is there a warning about this anywhere? If there isn't, there should be. I'm on 512k ADSL, and it's annoying. I'd hate to think what it's like for 56k'ers.--Drat (Talk) 03:02, 17 January 2006 (UTC)
replies: text: Sometimes you want a thumbnail to have more colours - especially when the image is black and white. I have proposed to developers that Mediawiki add a feature for explicitly specifying the colour count for a thumbnail, and it performs palette selection and reduction automatically. But I haven't entered a bug for this yet and it certainly hasn't been added yet. In the meantime, if you really have a filesize problem, simply upload a second thumbnail version of the image (on the Wikipedia where the article using it lives, not Commons), crosslink the two, and put a big bold notice explaining its purpose. I've done this in the past with some of my images. Deco 05:39, 24 January 2006 (UTC)

text: http://bugzilla.wikimedia.org/show_bug.cgi?id=1757 Plugwash 12:45, 24 January 2006 (UTC)
thread_title:  scaling problems. 

message: :"That said, PNG does not support Exif image data from sources such as digital cameras, which makes it problematic for use amongst amateur and especially professional photographers."
Sure png doesn't call the feature exif but it certainly supports storage of arbitary name-value pairs which is what exif data basically consists of. Plugwash 17:05, 5 June 2006 (UTC)
thread_title:  Exif 

message: Since PNG is a lossless image format and it compresses better than TIFF does (and apparently better than PSD, if my test is accurate), could it be used for image editing? I'm not talking about a total replacement. There are probably limitations and problems with using PNG this way. However, would the average user be better off using PNG instead of TIFF when editing images? Photoshop won't let me save an image as a PNG, except as a copy (or a JPEG). However, it will let me save it as a TIFF or PSD, presumably since there is no loss of data. I did a test on a 5.9 MB JPEG image. I saved it as a TIFF and got an image size of 26.2 MB and as a PNG, which gave an image size of 12.2 MB (47% of 26.2). It did take longer to save the file as a PNG, though (10 seconds or so compared to a second or two). A table of the size with the different formats is below. Unfortunately, the image was too wide to save it as a PICT. 
*JPG 5.9 MB (original)
*GIF 5.2 (just for the hell of it)
*JP2 7.7 (highest quality lossy)
*JP2 10.7 (lossless)
*PNG 12.2
*PDF 21.4 (highest quality lossy)
*PSD 25.8
*TIFF 26.2
*BMP 26.2
*Photoshop 2.0 26.2
*Photoshop Raw 26.2
*PDF 39.6 (no compression)
*Photoshop EPS 44.3
It looks like JP2 lossless is the best if you want the smallest file size and lossless compression. PNG isn't much bigger and might be more compatible. PSD, TIFF, BMP, Photoshop 2.0 and Raw are about the same in file size, so I guess it depends which has the features you need, like PSD which supports layers and stuff, and whether there is a compatibility issue. PDF, of course, is not the way to go when you want a small file size, losslessly or otherwise, and neither is EPS. 
I'm suprised that the JP2 lossless is so small, less than double (the comparison might be screwed up since it was saved as a regular JPG first, though) and it is even less of a step up from the highest quality lossy JP2. If it becomes widely supported, perhaps it would be better just to use JP2 lossless as the format for the final image, rather than the highest lossy setting. JP2 lossless or RAW could be used in the camera and PSD could be used while editing, if necessary. -- Kjkolb 20:50, 3 July 2006 (UTC)
replies: text: For the home editor using a basic tool PNG is ideal, pros may find its limited color depth support and lack of things like layers an issue though. Plugwash 21:13, 3 July 2006 (UTC)
thread_title:  PNG vs. TIFF and PSD for image editing 

message: The chart at PNG#Color depth makes it seem like PNG is limited to 16 bits per pixel, but PNG#Technical comparison with GIF says, "PNG gives a much wider range of color depths than GIF (truecolor up to 48-bit compared to 256-color), allowing for greater color precision, smoother fades, etc." Is this an error or is it talking about different things? Also, in the post above, Plugwash says that PNG has limited color depth support. Is the lack of support in the PNG format itself or is it in programs that create PNGs? What color depth are PNGs limited to, due to the format and/or application support? -- Kjkolb 08:00, 11 July 2006 (UTC)
replies: text: PNG is limited to 16 bits per channel, as the table at PNG#Color depth says. But there can be as many as 4 channels (red, green, blue and alpha) with 16 bits each, which gives 64 bits per pixel. --Zundark 08:32, 11 July 2006 (UTC)

text: The following discussion is an archived debate of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section. 
The result of the debate was no move. -- tariqabjotu (joturner) 01:29, 11 August 2006 (UTC)
thread_title:  Color depth 

message: How about the problem with PNGs not loading in IE 4 or 5, despite the alleged basic support?  This is not about the transparency issue but getting them to load at all.  Is there any information on this?  I have searched the Net and have not found information anywhere.  Surely there must be a plugin or workaround to fix this.  Stovetopcookies 18:10, 24 August 2006 (UTC)
thread_title:  PNGs not loading in IE 4 or 5 

message: 9 times out of 10, if someone searches for this topic and winds up here, they need to know basic information.  The info here now is super thorough, complex, and way over our heads!  The folks putting this together failed in that they never told what a png file is and how to use it.  Way too technical - I still don't know how to print, view, or imbed on my website!  Can & should I convert it to a more standard file extension? —Preceding unsigned comment added by Genihanna (talk • contribs) 
:The intro pretty clearly states what png is and why it was created
:"PNG (Portable Network Graphics) is a bitmap image format that employs lossless data compression. PNG was created to both improve upon and replace the GIF format with an image file format that does not require a patent license to use."
:If those words don't mean anything to you then i'd suggest reading the linked articles as you will not be able to understand the differences between image formats without a grasp of them.
:As to your other questions you have to realise that wikipedia is not a howto guide. It is not our purpose to go telling users how to use specific applications to perform specific tasks on files. Any decent image editor will support loading and saving png files. There is nothing special about embedding a png in a web page it is just the same as any other image format. Plugwash 00:04, 21 October 2006 (UTC)
thread_title:  Still unanswered 

message: Hey, I realize that this is not exactly the forum for this question, but I am looking for a relatively obscure answer that no one has been able to help me with so far.  I'm trying to make stimulus for a psych experiment using CIE space, so I made it in photoshop with LAB color, a CIE space, but I can't save it as anything but a Tiff which most other applications won't load.  I can save it as an 8-bit LAB color tiff, which will sort-of load, or a 16-bit RGB color .PNG file, which will load.  The problem is that the two look very different, and I dont know which is closer to the true 16-bit LAB color.  Any ideas?
thanks and sorry for posting a somewhat irrelevant question here.
Oh, to clarify, The program I am using (SuperLAB 4.0) only supports .bmp,.png,.tif, and .jpg.  Photoshop does .tif just fine, but it looks like SuperLAB, along with most other programs, can't handle LAB color in 16 bits.  The Image quality doesn't matter much, its a simple line drawing, but the color is super-important.  I need LAB Cyan to look as close as possible to what it really is, so is 8 bit LAB (tiff) closer than 16 bit RGB (ping)? I also have the option of an 8 bit RBG jpeg, but im guessing thats a joke.  Thanks again
:i'd imagine 8 bit per channel lab color would be more likely to be indistinguishable than 16 bit "RGB" but i'm no expert. Plugwash 23:44, 20 October 2006 (UTC)
thread_title:  Color Question - LAB/RGB/ 8/16 bit 

message: "However, as a 7-pass scheme, it tends to reduce the data's compressibility more than simpler schemes."  Is this accurate?  Based on the context, this seems to be saying the opposite.  Is this an unintentional double-negative? ("reducing compressability" would mean it can't be compressed as well) BeboGuitar 00:49, 11 November 2006 (UTC)
replies: text: It is true that adding Adam7 interlacing to a PNG will increase its file size in most cases. I've never seen Adam7 interlacing decrease the file size of a PNG. It also seems to take longer to save PNGs using Adam7 interlacing than without. The interlacing feature in GIFs doesn't increase the file size nearly as much as the interlacing feature in PNGs, and in some cases interlacing doesn't increase the file size at all in GIFs. Jecowa 12:36, 11 November 2006 (UTC)
replies: text: interlacing is a compromise, you send the raw image data in a different order which allows a low res version to be constructed quickly but in doing so you reduce the compressibility of the data. Generally the more passes you have the bigger the affect on compressibility. Its a balance, is having low res information availible to the user quickly more important than the overall download time and if so how low res is low res, png decided on a 7 pass system proposed by a mailing list member at the time which was iirc based on some rough tests with imagemaps. Now we are stuck with that scheme. Plugwash 17:57, 12 November 2006 (UTC)
replies: text: But there's no point optimising an interlace system for low file size. You already have a low file size choice - don't interlace. If you want to interlace, it makes sense to choose an interlace system that gets something recognisable up quickly. And the PNG scheme is very good at that; much, much better than GIF by an order of magnitude. And the extra file size cost isn't much. --KJBracey 21:09, 12 November 2006 (UTC)
thread_title:  Interlacing 

message: (I guess no one has discussed it yet as per discussion request.)  Rather than have a stub article for libpng, I agree with merging the libpng article into this one. 2*6 02:42, 6 January 2007 (UTC)
replies: text: If no comments in next couple of days, I'll go ahead and merge. 2*6 12:35, 12 January 2007 (UTC)
replies: text: Without any concurrence from anyone, I decided I'm not comfortable doing the merger, although I still think it is good idea. I noticed as I started merging that zlib has its own article, which is what made me hesitate now. – 2*6 13:20, 16 January 2007 (UTC)

text: Well, that's 5 saying "Oppose" (6 if you count User:Dozen's comment from 16 January 2007) to 0 who support. So I've WP:BOLDly closed the poll and removed the merge tags. Cheers, CWC 17:19, 29 March 2007 (UTC)
thread_title:  Merging the libpng article 

message: I added 3 greyscale images to the "Color depth" section.  I'm not sure it is the best spot for them.  Also, if others feel they are not useful, I would not object to them being removed from the article. 2*6 12:35, 12 January 2007 (UTC)
thread_title:  Added 3 greyscale images 

message: Would anyone be able to transfer  to a PNG with a transparent background? I guess I don't have the skill. --Daysleeper47 20:16, 31 January 2007 (UTC)
replies: text: It has a transparent background in . The JPEG is compressed and has artifacts. Would you be able to get a lossless (not a JPEG) version of this image? It would make the image higher in quality. Jecowa 20:54, 31 January 2007 (UTC)
replies: text: I did not create it. Bobanny created it but wasn't sure how to make it transparent. He created it as jpg. I will chat with him and see what he can do. Thanks for the help Jecowa. --Daysleeper47 21:44, 31 January 2007 (UTC)
replies: text: Also, how do I reconcile the fact that I created an image with the same name only on en.wiki which is different from the one which Bobanny created? When I apply the image to articles, the en.wiki image appears, not the Commons image. --Daysleeper47 21:53, 31 January 2007 (UTC)
thread_title:  Converting to PNG 

message: PNG redirect should be to the country. Sad mouse 04:07, 12 March 2007 (UTC)
replies: text: Don't be silly. Nobody would say he went to pee-en-jee for the holidays. Shinobu 19:08, 26 August 2007 (UTC)
thread_title:  Redirect 

message: On other Wikis, I have tried to make thumbnails of some PNG-files, but it doesn't work very well. Unlike gif or jpg, for some reason the png's color depth gets decreased to just nuances of a particular color, i.e. if the background is green, the whole image turns into shades of green. Why does this happen, and is it some way one could get around it? 惑乱 分からん * \)/ (\ (< \) (2 /) /)/ * 15:44, 28 May 2007 (UTC)
replies: text: 23-Aug-2007: Some versions of some browsers have trouble displaying PNG files (but not GIF or JPEG).  See alpha/gamma color problems displaying PNG in IE7 (above): Internet Explorer 7.  For Wiki (as of 2006 to August 2007), the Wiki thumbnail resizing software still displays GIF files 3x times faster than PNG (and JPEG 5x to 21x times faster than PNG).  Even though PNG files store as slightly (5%-25%) smaller than GIF, the PNG files expand to a whopping 3x times the size of the tiny GIF thumbnails, clogging the transfer of Wikipedia or Wikimedia Commons PNG thumbnails.  The Wiki problem is typically massive PNG-thumbnail gigantism:  some PNG thumbnails have displayed 21x (twenty-one) times (painfully) slower than same-size JPEG images.  I've been waiting since mid-2006 for the Wiki-PNGs to thumbnail faster, but the Wiki software is not improving that fast.  Those bizarre Wiki-PNG thumbnails are much (often 8x times) larger than the original PNG stored image.  People who don't study Wiki performance have been shocked at the massive Wiki-PNG thumbnails, perhaps because equivalent GIFs & JPEGs were deleted when auto-converted to PNG, and the deleted original GIF/JPEGs were no longer there for comparisons. Also, some people who convert to PNG have been censoring Wiki information about slow PNG performance & blurry results. -Wikid77 07:05, 23 August 2007 (UTC)
replies: text:  That rant didn't answer his question, nor was it anywhere as convincing as a good full writeup somewhere. I guess when the Illuminati are actively censoring you, though...--Prosfilaes 10:32, 23 August 2007 (UTC)
thread_title: PNGs and thumbnails?