File talk:Airbus A300 Beluga v1.0.png

These files behave oddly

The enlarged plans display in my browser as black on a dark gray background with a transverse cross-section in white/light-gray to the lower right. When downloaded, the resultant file displays in my image viewing program (IrfanView) as a black field with only the light cross-section showing. Manipulating the brightness, gamma and contrast show that the rest of the image is not there at all.

I think something is wrong here and perhaps the original up-loader or a knowledgeable person can explain or fix this.

Note that the versions of these files on their Wikipedia page (http://en.wikipedia.org/wiki/File:A300Belugav1.0.png) behave correctly. —Blanchette (talk) 20:22, 18 July 2012 (UTC)

This may be a browser issue since I just returned to the Wikipedia page and it now has the same issues for me as the Commons page. I am using Firefox 14.0.1 on Windows XP x64. —Blanchette (talk) 20:39, 18 July 2012 (UTC)

Hi Blanchette, this is definitely a browser issue. Since version 11 or so, when displaying a single JPG or PNG image, Firefox centers the image in the window and adds a dark gray background behind it. Since this PNG file has transparent backdrop what we are seing is the Firefox-added dark gray background, on top of which the black lines of the drawing are visible. This is filed as Firefox bug #728085. It may get fixed soon, depending on the amount of interest it obtains. Ariadacapo (talk) 06:43, 19 July 2012 (UTC)

Yes, this is the first irritating "feature" I have noticed on Firefox and I hope it is fixed soon especially if it violates the PNG specification. I have discovered that my download of this was not defective and that IrfanView displays this type of PNG image with a transparent background correctly as long as one sets Options > Properties/Settings > Viewing with "Show PNG/TIF/TGA/DDS alpha/transparent color" CHECKED and have set "Main window color" to white or another light color.

I do have reservations about Wikimedia using this kind of PGN with transparency in that it seems to demand that the user be set up to accommodate an unknown convention that such images will be displayed on a white background. I notice some very light gray dimensioning lines in this file that are invisible against light gray. If there is a requirement in the PNG specification that all such files will be displayed on a white background then I suppose it is justifiable, if not exactly user friendly, but I doubt that the specification specifies this since I gather transparent PNG was designed, among other things, to be used on the kind of patterned backgrounds one finds on web pages. Furthermore, a white-line transparent-background PNG on a white display background will be just as invisible as black on black! Is there a good reason to use these transparent-background files on Wikimedia projects? —Blanchette (talk) 05:38, 4 August 2012 (UTC)

This issue is not a "violation" of the PNG standard. Transparent background images are incredibly useful. Adding a white background on a transparent PNG is trivially easy, removing a white background on a non-transparent PNG is much harder (due to anti-aliasing). Transparent background images allow for much more flexibility in usage. We should not change this to accommodate for a mere browser display quirk. Ariadacapo (talk) 06:36, 4 August 2012 (UTC)

Thanks, Ariadacapo. I was not proposing eliminating this image format, just asking the reason for its use. Also, my question was unrelated any browser quirk since. as I remarked, white on white is just as invisible as black on black, etc. I have no reason to doubt your pronouncement that this format is incredibly useful, though an example or two would be helpful for novices such as myself. I do understand your point about anti-aliasing where the image is anything but monochrome. —Blanchette (talk) 22:12, 7 August 2012 (UTC)

Hi Blanchette. Sorry for the misunderstanding. I guess since no physical device is actually transparent, one is always going to have to pick a pattern or a color to fill the "transparency" in images. In that sense, "transparent" may be interpreted as "left to the choice of the user".

The best example I can think of is the use of images in presentation slides (I do this all the time for work). In such cases the background can be changed (black, white, gradient, company template, etc) without having to re-adapt the image. For aircraft plans I am used to filling the inside of profiles in white, like so.

Finally, regarding anti-aliasing. The technique uses multiple shades of gray to represent what is essentially a "black and white" image, as shown in File:Aliasing a.png. If that is done over a transparent background, then the shades of gray are defined as partly-transparent black. All of the the transparency in the image can be replaced with white quickly, but going the other way is much harder (it is much more time-consuming to extract the "whiteness" in each pixel and replace this with transparency).

Note that this problem disappears entirely when using SVG instead of PNG, as I wish the author of the present files would do for his excellent work. Ariadacapo (talk) 09:14, 9 August 2012 (UTC)

Thank you for the explanations, Ariadacapo. I am happy to report that my current Firefox version, 15.0.1, displays these files on a white background, so apparently the developers listened to our bug reports. —Blanchette (talk) 06:32, 14 September 2012 (UTC)