explain xkcd - User contributions [en]

Talk:1190: Time

2013-03-25T07:43:02Z

220.226.203.202:

Pretty sure we're just getting trolled with this one [[Special:Contributions/99.108.190.136|99.108.190.136]] 04:48, 25 March 2013 (UTC)

Can't tell if this is emo xkcd or trolling xkcd. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:53, 25 March 2013 (UTC)

Something seems a little fishy because the image url is different than normal. [[User:Bugefun|Bugefun]] ([[User talk:Bugefun|talk]]) 04:55, 25 March 2013 (UTC)
:Maybe the comic slowly changes throughout the day. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:56, 25 March 2013 (UTC)
::Oh god, it does. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:57, 25 March 2013 (UTC)
:::When uploading different versions of the image, use the naming convention time[iterationNumber].png. We'll compile all the images into one and display them as per [[Traffic Lights]]. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:05, 25 March 2013 (UTC)
::::Alright, so the comic appears to be switching between two states here: between [[media:time2.png|this]] and [[media:time3.png|this]]. If nothing new happens, I'll get to clipping the comics together. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:28, 25 March 2013 (UTC)
:::::Whoop, nope, [[media:time4.png|this]] just came up. Is there more to come? '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:34, 25 March 2013 (UTC)
::::::Alright, so a new one is posted every half-hour. Whoopee. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 06:06, 25 March 2013 (UTC)
:::::::And there's a new one! Megan leaning back and looking up...
::::::::Well, the image changed, who has the time to make a script to catch the new images and compile them into a gif? https://dl.dropbox.com/u/932170/time.png [[User:Statharas.903|Statharas.903]] ([[User talk:Statharas.903|talk]]) 07:14, 25 March 2013 (UTC)

[[Special:Contributions/72.21.198.66|72.21.198.66]] 05:11, 25 March 2013 (UTC)It could be a reference to the old proverb " time and tide wait for none" Cueball and the girl could be waiting for the tide in the beach! (Just a guess)[[Special:Contributions/72.21.198.66|72.21.198.66]] 05:11, 25 March 2013 (UTC)

The picture does chance with time. The URL includes a changing timestamp that I can't decipher. Compare these two URLS (which have slightly different images:
http://imgs.xkcd.com/comics/time/8eb156cce408df8bb83528382d6a2aa2ce6c74f3c573fd12b058cd1c56420672.png
http://imgs.xkcd.com/comics/time/1e349a579b5f9b5ed487ddf7e88244b70330941ddedac9c6abf6ed2e3f589b97.png

Perhaps there is a way to hack the URL to view future images. [[Special:Contributions/199.30.248.121|199.30.248.121]] 05:29, 25 March 2013 (UTC)
: I would also like to add that knowing randall, these are not the only images. For all we know, the image will still be changing in 5 years while a tree grows in front of them. My point is: Are the URLs hackable, or did he encrypt them? [[Special:Contributions/199.30.248.121|199.30.248.121]] 05:33, 25 March 2013 (UTC)

Likely there is a way to hack the URLs; they look like some sort of hash, probably a hashed timestamp. Of course, he could easily have added some salt to the hash, making it significantly *harder* to hack. But they're strings of a specific length, so it should be pretty easy to bruteforce it, fetch all the images, and then (maybe) reverse-engineer the sequence. *That* all depends on how many of them there are. [[Special:Contributions/76.90.249.178|76.90.249.178]] 05:44, 25 March 2013 (UTC)
:Good god, do you see how many digits are *in* that hash? The sun'll have burned out by the time we've tested every possible combination of digits. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:47, 25 March 2013 (UTC)

It seems that the image is updated every 1/2 hour. [[Special:Contributions/152.23.97.150|152.23.97.150]] 06:17, 25 March 2013 (UTC)
: Given that the images switch back and forth between other images already seen, and that the comic should be viewable in the future, it seems unlikely that it's any thing like a simple sha256 of part of the timestamp. I think it's more likely a function of half-hours and minutes (assuming we continue to get a new possible image every half-hour). [[Special:Contributions/99.153.248.206|99.153.248.206]] 06:59, 25 March 2013 (UTC)

::: The images do cycle, yes. But for some reason I have never seen the img where Megan is looking behind her. Also wouldn't it be difficult to show a sequential story (like the rising tide) if the previous images keep cycling ?

Hash appears to be SHA-256. I tried some obvious hashes ("1", "11901", "1190_1", "1190.1") to no avail. Maybe this is HMAC-SHA256? Also, I would suggest trying Unix timestamps. [[Special:Contributions/131.156.236.149|131.156.236.149]] 06:19, 25 March 2013 (UTC)
: I've been trying to make educated guesses as to what's being hashed here: http://www.xorbin.com/tools/sha256-hash-calculator ... he could also be using hash(hash2(value)) which would be virtually impossible to crack. [[Special:Contributions/99.153.248.206|99.153.248.206]] 06:59, 25 March 2013 (UTC)

It's entirely possible that the "hash" is actually randomly generated. Just a thought. [[Special:Contributions/129.21.119.153|129.21.119.153]] 07:03, 25 March 2013 (UTC)

Alright, this is probably not going to work, but I'm trying to exploit Randall's awesomeness here. Maybe he decided to take the time-stamps from the user? I don't know if that's even possible... That would then allow people in different time zones to obtain different images simultaneously. (What's the corollary of Godwin's law for a bunch of math-and-science nerds and relativity? Is there one?) Clicking the img src url on the comic's html page, give me this: http://imgs.xkcd.com/comics/time/752687b61523144c61736cd89f8c153dc41e19128f72d78d44947ff800f057fa.png : Never mind.. apparently others see the same image too.

Could he be doing this live? Monitoring the discussion on the net? Collaborative, crowdsourced comic-ing? Reminds me of those you-decide-what-the-character-does-next-and-flip-to-appropriate-page parallel plot novels.

[[Special:Contributions/220.224.246.97|220.224.246.97]] 07:14, 25 March 2013 (UTC)

Let's just compare the two pictures and see how the bottom right changes, which I believe is water and they are indeed waiting for the tide. [[User:Statharas.903|Statharas.903]] ([[User talk:Statharas.903|talk]]) 07:19, 25 March 2013 (UTC)
:I'm adding urls to pictures bellow, edit freely.
::They change every 5 minutes, will try to keep track.

http://www.explainxkcd.com/wiki/images/f/f8/time.png
http://imgs.xkcd.com/comics/time/1e349a579b5f9b5ed487ddf7e88244b70330941ddedac9c6abf6ed2e3f589b97.png
http://imgs.xkcd.com/comics/time/752687b61523144c61736cd89f8c153dc41e19128f72d78d44947ff800f057fa.png
http://dl.dropbox.com/u/932170/timeasdf.png
http://dl.dropbox.com/u/932170/time6.png

Talk:1190: Time

2013-03-25T07:06:51Z

220.226.203.202:

Pretty sure we're just getting trolled with this one [[Special:Contributions/99.108.190.136|99.108.190.136]] 04:48, 25 March 2013 (UTC)

Can't tell if this is emo xkcd or trolling xkcd. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:53, 25 March 2013 (UTC)

Something seems a little fishy because the image url is different than normal. [[User:Bugefun|Bugefun]] ([[User talk:Bugefun|talk]]) 04:55, 25 March 2013 (UTC)
:Maybe the comic slowly changes throughout the day. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:56, 25 March 2013 (UTC)
::Oh god, it does. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:57, 25 March 2013 (UTC)
:::When uploading different versions of the image, use the naming convention time[iterationNumber].png. We'll compile all the images into one and display them as per [[Traffic Lights]]. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:05, 25 March 2013 (UTC)
::::Alright, so the comic appears to be switching between two states here: between [[media:time2.png|this]] and [[media:time3.png|this]]. If nothing new happens, I'll get to clipping the comics together. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:28, 25 March 2013 (UTC)
:::::Whoop, nope, [[media:time4.png|this]] just came up. Is there more to come? '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:34, 25 March 2013 (UTC)
::::::Alright, so a new one is posted every half-hour. Whoopee. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 06:06, 25 March 2013 (UTC)
:::::::And there's a new one! Megan leaning back and looking up...

[[Special:Contributions/72.21.198.66|72.21.198.66]] 05:11, 25 March 2013 (UTC)It could be a reference to the old proverb " time and tide wait for none" Cueball and the girl could be waiting for the tide in the beach! (Just a guess)[[Special:Contributions/72.21.198.66|72.21.198.66]] 05:11, 25 March 2013 (UTC)

The picture does chance with time. The URL includes a changing timestamp that I can't decipher. Compare these two URLS (which have slightly different images:
http://imgs.xkcd.com/comics/time/8eb156cce408df8bb83528382d6a2aa2ce6c74f3c573fd12b058cd1c56420672.png
http://imgs.xkcd.com/comics/time/1e349a579b5f9b5ed487ddf7e88244b70330941ddedac9c6abf6ed2e3f589b97.png

Perhaps there is a way to hack the URL to view future images. [[Special:Contributions/199.30.248.121|199.30.248.121]] 05:29, 25 March 2013 (UTC)
: I would also like to add that knowing randall, these are not the only images. For all we know, the image will still be changing in 5 years while a tree grows in front of them. My point is: Are the URLs hackable, or did he encrypt them? [[Special:Contributions/199.30.248.121|199.30.248.121]] 05:33, 25 March 2013 (UTC)

Likely there is a way to hack the URLs; they look like some sort of hash, probably a hashed timestamp. Of course, he could easily have added some salt to the hash, making it significantly *harder* to hack. But they're strings of a specific length, so it should be pretty easy to bruteforce it, fetch all the images, and then (maybe) reverse-engineer the sequence. *That* all depends on how many of them there are. [[Special:Contributions/76.90.249.178|76.90.249.178]] 05:44, 25 March 2013 (UTC)
:Good god, do you see how many digits are *in* that hash? The sun'll have burned out by the time we've tested every possible combination of digits. '''[[User:Davidy22|{{Color|purple|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 05:47, 25 March 2013 (UTC)

It seems that the image is updated every 1/2 hour. [[Special:Contributions/152.23.97.150|152.23.97.150]] 06:17, 25 March 2013 (UTC)
: Given that the images switch back and forth between other images already seen, and that the comic should be viewable in the future, it seems unlikely that it's any thing like a simple sha256 of part of the timestamp. I think it's more likely a function of half-hours and minutes (assuming we continue to get a new possible image every half-hour). [[Special:Contributions/99.153.248.206|99.153.248.206]] 06:59, 25 March 2013 (UTC)

Hash appears to be SHA-256. I tried some obvious hashes ("1", "11901", "1190_1", "1190.1") to no avail. Maybe this is HMAC-SHA256? Also, I would suggest trying Unix timestamps. [[Special:Contributions/131.156.236.149|131.156.236.149]] 06:19, 25 March 2013 (UTC)
: I've been trying to make educated guesses as to what's being hashed here: http://www.xorbin.com/tools/sha256-hash-calculator ... he could also be using hash(hash2(value)) which would be virtually impossible to crack. [[Special:Contributions/99.153.248.206|99.153.248.206]] 06:59, 25 March 2013 (UTC)

It's entirely possible that the "hash" is actually randomly generated. Just a thought. [[Special:Contributions/129.21.119.153|129.21.119.153]] 07:03, 25 March 2013 (UTC)

1187: Aspect Ratio

2013-03-21T10:05:44Z

220.226.203.202: Teeny typo

{{comic
| number = 1187
| date = March 18, 2013
| title = Aspect Ratio
| image = aspect ratio.png
| titletext = I'm always disappointed when 'Anamorphic Widescreen' doesn't refer to a widescreen Animorphs movie.
}}

==Explanation==
Aspect ratio is the relationship between the width and height of the image (and in this case, a video) and is denoted in a ratio of <width>:<height> - usually either in lowest common denominator, or with a decimal width to a height of "1". Up until the 1990s, all televisions and most computer monitors (CRT tube and LCD) were in the standard 4:3 aspect ratio, called "fullscreen" (meaning the width is 4/3 or 1.33... times the height). When HDTV was developed, the standard for television screens changed to 16:9 (width being 16/9 or 1.77... times the height), called "widescreen" (although widescreen can also refer to a number of even wider ratios used in feature films). Computer monitors are now available in widescreen ratios, though fullscreen remains common as well.

Letterboxing is a process whereby an image which does not fully fill a screen is expanded to fill the screen by the addition of further material (mattes). Usually this is done with the addition of black bars in the empty space. One example of why this was necessary was widescreen films on VHS cassette. VHS could only record and play back 4:3 images. Thus, in order to display a widescreen film, the rest of the VHS's 4:3 image had to be filled with horizontal black bars at the top and bottom of the image. Those bars were part of the video information recorded on the cassette.

When DVDs were introduced, many DVDs also had letterbox bars on the DVD's full screen image. With the increased popularity of widescreen televisions, DVD players were improved to offer {{w|anamorphic widescreen}}, in which the full widescreen image is horizontally rescaled (shrunk) into a 4:3 size, which the player then was able to display stretched horizontally back to the proper widescreen aspect.

With the advent of Blu-Ray, video is generally encoded in whatever its proper aspect ratio is intended to be, and the player itself is left to appropriately matte the image.

The problem with letterboxed video (such as a 16:9 video letterboxed for 4:3) is that if one tries to watch the video on a 16:9 widescreen, where the image ''should'' fill the whole screen, instead the 4:3 letterboxed image fills part of the screen with further vertical mattes on the left and right of the image, thus producing an image much smaller than it needs to be, with mattes on all four sides. Some TVs or media players can zoom to help resolve the issue, although the video resolution usually suffers. By encoding only the video itself and allowing the player to do the matting, the video can be seen as large as possible on any given screen.

''{{w|Animorphs}}'' is a late-90's to early-00's young adult book series about shape-shifting teens who turn into animals to fight body-snatching aliens. Sony held the rights to create a film, but never made use of them, beyond creating URLs for a proposed movie on December 11th, 2012.

In this comic, Randall appears to be complaining about the issue of widescreen videos which have been rescaled to 4:3 by adding mattes to the top and bottom and uploaded on sites like YouTube. He is probably annoyed by the fact that on his widescreen monitor, TV or mobile device, the video (as noted above) does not fill the screen because of the letterboxing. In some cases, uploaders also take video and rescale it to the point where the image is improperly compressed horizontally or vertically, even without letterboxing. This is more akin to the car crushing Randall depicts in the comic.

A note is that, if someone managed to "expand" the car, the car would not be "un-crushed" and probably even weakened even more, referencing the bigger damage done when letterboxed video is attempted to be "expanded" to its original ratio, distorting the video quality.

==Transcript==
:[A car is crushed in a large black clamp.]
:Whenever someone uploads a letterboxed 16:9 video rescaled to 4:3, I do this to their car.

{{comic discussion}}

Talk:401: Large Hadron Collider

2013-02-16T04:01:40Z

220.226.203.202: Signs of vandalism

Why is there is a link to some Higgs Boson music on this page ?