explain xkcd - User contributions [en]

Talk:2414: Solar System Compression Artifacts

2021-01-24T17:15:49Z

Efalk:

"([Compression artefacts] may become literally unnoticeable because hexadecimal color values are discrete[...]" - disagree. Artefacts exist ''because'' of a discrete nature. Either of the RGB(/HSV/whatever) granularity, the lower the colour depth, or of the method used to get around the overheads of storing literal 24+ bits of colour-depth across a given image size. TrueColo(u)r should escape ''perceived'' colour-banding, but any image editor knows (or relies upon) that any flood-fill/by-colour-selection used with an absolute drift range away from the datum spot less than that across a gradient spills away from it can highlight 'hidden' edges between (say) #789ABC and #789BBC. What we have here is low bit-depth (grey-shade or equal-RGB, apparently 4-bit(/each), counting the 16 bands thanks to the mach-banding) non-dithered band-shading of a possibly nuanced (fractal?) shade fall-off. Possibly a 2D slice through 3D (or more, e.g. if animated) of voxelated (or hypervoxelated) stored values, which use up a ''lot'' of space in the Universe Simulator. Perhaps there's also something like Discrete Cosine Transform compression for easier block/chunk storage, retrieval and/or generation-on-demand (with detailed deltas for complex overlaying features such as Voyager). Because the Creator/Programmer of the universe has limited storage/processor cycles! [[Special:Contributions/141.101.105.122|141.101.105.122]] 01:39, 21 January 2021 (UTC)
:tl;dr? — [[User:Sqrt-1|The 𝗦𝗾𝗿𝘁-𝟭]] [[User talk:Sqrt-1|talk]] [[Special:Contributions/Sqrt-1|stalk]] 13:16, 21 January 2021 (UTC)
::TLDR is this Tom Scott video on the topic: https://youtu.be/h9j89L8eQQk. Short version: the difference between blacks #010101 and #020202 (a doubling of brightness) is more noticeable than the difference between whites #FEFEFE and #FDFDFD (a 0.00001% change in brightness). If your picture is dark, and especially if it is compressed, you will often get ugly bands of different shades of black. [[Special:Contributions/108.162.237.28|108.162.237.28]] 16:50, 22 January 2021 (UTC)
I would suggest that more emphasis needs to be placed on 'dynamic range' and 'undetectable' in this explanation. Particularly noticeable in streaming video codecs, you often can't decipher any information in dark scenes/regions. So the joke is that the map beyond here is empty, mostly because it is too far down in the dynamic range of our lossy observations. [[Special:Contributions/108.162.219.80|108.162.219.80]] 17:36, 21 January 2021 (UTC)
:Re "...stretches out over maybe a dozen such low-res pixels/AUs, which is equivalent to slightly more than the radius of Saturn's orbit or the entire diameter of Jupiter's!", this assumes that Jupiter and Voyager are the same distance from the imaginary "camera". I can completely cover the moon with my thumb, but that does not imply that they are similar in size, because my thumb is closer to my eye. ''(Unsigned!)''
::I presume that this is the 'data' version of our system, straight from the 'cosmic computer' behind reality, viewed orthographically like a Minecraft map. But it matters not. The text quoted clearly gives scale context (on the justifiable presumption that the low-res grid is a 1AU-sized display of solar particle distribution) that "the range of the map the Voyager covers is like the size of these orbits". Just like "the area of the sky my thumb obscures is roughly a Moon-width". [[Special:Contributions/141.101.104.241|141.101.104.241]] 01:18, 22 January 2021 (UTC)
:Re: "The Voyager image (and track) is overlaid at finer resolution", if it not unheard-of for a compression algorithm to render, say, 32x32 pixel blocks as if they were single, larger pixels if their immediate neighbors are almost the same shade, while rendering small, detailed, and high contrast portions of the image at a higher resolution. No "overlay" required. ''(Still unsigned!)''
::Within an area of finer details, artefacts ''would'' be seen as the "meh, this is just one block" attitude is changed to incorperate detail of interest within a sub-block. There's no sign of fringe-artefacts (other than normal XKCS antialiasing of lines against background). I'd say it was a "solar wind" low-detail layer over which is incorporated a "Voyager" standard-detail layer with transparency, not a single layer of subject-aware tunable blockwise compression. (It might have come out differently if the composition was saved in an actual lossy-compression, by Randall, rather than .png, but for different reasons. Bit that's a meta-discussion issue, not nerd-sniping.) [[Special:Contributions/141.101.104.241|141.101.104.241]] 01:18, 22 January 2021 (UTC)
This doesn't just happen in old images. I still see this frequently when watching movies, even new ones, where what should be a smooth gradation of tones shows steps. The other obvious defect is poor sprite handling, which causes artifacts like someone's facial features not moving with their head movements.
I'm not sure dithering would be a useful way to dispel the banding, since dithering would increase the compressed data size because you no longer have large areas of all-the-same-pixel-value.
The banding could also be an artifact of the decompression. If you consider that a format like JPEG uses something like Fourier transforms it seems it should be able to represent a gradation easily and the stepped banding with difficulty, so I might be tempted to blame the banding on the decompression code.[[Special:Contributions/108.162.241.70|108.162.241.70]] 13:46, 22 January 2021 (UTC)

== Source of Voyager 1 ==

Given Voyager 1's distance and age now, wouldn't it be more appropriate to change the opening explanatory sentence to "Voyager 1 is a space probe launched from Earth in 1977."
The only sentient creatures who may still care about its origins in the United States are probably also from the United States. The next sentient beings to encounter Voyager 1 will have no understanding of what the United States is or was.

One more point: I think this XKCD is a play on the fact that every few years we hear once again that "Voyager has left the solar system". First because it passed the termination shock, then because it passed the heliopause. [https://solarsystem.nasa.gov/news/784/nasas-voyager-2-probe-enters-interstellar-space/ This article from NASA] says that Voyager won't be officially out of the solar system until it passes the Oort cloud. These milestones seem arbitrary, so why not make up one more? [[User:Efalk|Efalk]] ([[User talk:Efalk|talk]]) 17:13, 24 January 2021 (UTC)

Talk:2414: Solar System Compression Artifacts

2021-01-24T17:13:31Z

Efalk: This explainxkcd highlights the fact that Voyager seems to reach one arbitrary milestone after another.

"([Compression artefacts] may become literally unnoticeable because hexadecimal color values are discrete[...]" - disagree. Artefacts exist ''because'' of a discrete nature. Either of the RGB(/HSV/whatever) granularity, the lower the colour depth, or of the method used to get around the overheads of storing literal 24+ bits of colour-depth across a given image size. TrueColo(u)r should escape ''perceived'' colour-banding, but any image editor knows (or relies upon) that any flood-fill/by-colour-selection used with an absolute drift range away from the datum spot less than that across a gradient spills away from it can highlight 'hidden' edges between (say) #789ABC and #789BBC. What we have here is low bit-depth (grey-shade or equal-RGB, apparently 4-bit(/each), counting the 16 bands thanks to the mach-banding) non-dithered band-shading of a possibly nuanced (fractal?) shade fall-off. Possibly a 2D slice through 3D (or more, e.g. if animated) of voxelated (or hypervoxelated) stored values, which use up a ''lot'' of space in the Universe Simulator. Perhaps there's also something like Discrete Cosine Transform compression for easier block/chunk storage, retrieval and/or generation-on-demand (with detailed deltas for complex overlaying features such as Voyager). Because the Creator/Programmer of the universe has limited storage/processor cycles! [[Special:Contributions/141.101.105.122|141.101.105.122]] 01:39, 21 January 2021 (UTC)
:tl;dr? — [[User:Sqrt-1|The 𝗦𝗾𝗿𝘁-𝟭]] [[User talk:Sqrt-1|talk]] [[Special:Contributions/Sqrt-1|stalk]] 13:16, 21 January 2021 (UTC)
::TLDR is this Tom Scott video on the topic: https://youtu.be/h9j89L8eQQk. Short version: the difference between blacks #010101 and #020202 (a doubling of brightness) is more noticeable than the difference between whites #FEFEFE and #FDFDFD (a 0.00001% change in brightness). If your picture is dark, and especially if it is compressed, you will often get ugly bands of different shades of black. [[Special:Contributions/108.162.237.28|108.162.237.28]] 16:50, 22 January 2021 (UTC)
I would suggest that more emphasis needs to be placed on 'dynamic range' and 'undetectable' in this explanation. Particularly noticeable in streaming video codecs, you often can't decipher any information in dark scenes/regions. So the joke is that the map beyond here is empty, mostly because it is too far down in the dynamic range of our lossy observations. [[Special:Contributions/108.162.219.80|108.162.219.80]] 17:36, 21 January 2021 (UTC)
:Re "...stretches out over maybe a dozen such low-res pixels/AUs, which is equivalent to slightly more than the radius of Saturn's orbit or the entire diameter of Jupiter's!", this assumes that Jupiter and Voyager are the same distance from the imaginary "camera". I can completely cover the moon with my thumb, but that does not imply that they are similar in size, because my thumb is closer to my eye. ''(Unsigned!)''
::I presume that this is the 'data' version of our system, straight from the 'cosmic computer' behind reality, viewed orthographically like a Minecraft map. But it matters not. The text quoted clearly gives scale context (on the justifiable presumption that the low-res grid is a 1AU-sized display of solar particle distribution) that "the range of the map the Voyager covers is like the size of these orbits". Just like "the area of the sky my thumb obscures is roughly a Moon-width". [[Special:Contributions/141.101.104.241|141.101.104.241]] 01:18, 22 January 2021 (UTC)
:Re: "The Voyager image (and track) is overlaid at finer resolution", if it not unheard-of for a compression algorithm to render, say, 32x32 pixel blocks as if they were single, larger pixels if their immediate neighbors are almost the same shade, while rendering small, detailed, and high contrast portions of the image at a higher resolution. No "overlay" required. ''(Still unsigned!)''
::Within an area of finer details, artefacts ''would'' be seen as the "meh, this is just one block" attitude is changed to incorperate detail of interest within a sub-block. There's no sign of fringe-artefacts (other than normal XKCS antialiasing of lines against background). I'd say it was a "solar wind" low-detail layer over which is incorporated a "Voyager" standard-detail layer with transparency, not a single layer of subject-aware tunable blockwise compression. (It might have come out differently if the composition was saved in an actual lossy-compression, by Randall, rather than .png, but for different reasons. Bit that's a meta-discussion issue, not nerd-sniping.) [[Special:Contributions/141.101.104.241|141.101.104.241]] 01:18, 22 January 2021 (UTC)
This doesn't just happen in old images. I still see this frequently when watching movies, even new ones, where what should be a smooth gradation of tones shows steps. The other obvious defect is poor sprite handling, which causes artifacts like someone's facial features not moving with their head movements.
I'm not sure dithering would be a useful way to dispel the banding, since dithering would increase the compressed data size because you no longer have large areas of all-the-same-pixel-value.
The banding could also be an artifact of the decompression. If you consider that a format like JPEG uses something like Fourier transforms it seems it should be able to represent a gradation easily and the stepped banding with difficulty, so I might be tempted to blame the banding on the decompression code.[[Special:Contributions/108.162.241.70|108.162.241.70]] 13:46, 22 January 2021 (UTC)

== Source of Voyager 1 ==

Given Voyager 1's distance and age now, wouldn't it be more appropriate to change the opening explanatory sentence to "Voyager 1 is a space probe launched from Earth in 1977."
The only sentient creatures who may still care about its origins in the United States are probably also from the United States. The next sentient beings to encounter Voyager 1 will have no understanding of what the United States is or was.

One more point: I think this XKCD is a play on the fact that every few years we hear once again that "Voyager has left the solar system". First because it passed the termination shock, then because it passed the heliopause. [This article from NASA](https://solarsystem.nasa.gov/news/784/nasas-voyager-2-probe-enters-interstellar-space/) says that Voyager won't be officially out of the solar system until it passes the Oort cloud. These milestones seem arbitrary, so why not make up one more? [[User:Efalk|Efalk]] ([[User talk:Efalk|talk]]) 17:13, 24 January 2021 (UTC)

2363: Message Boards

2020-09-23T23:31:27Z

Efalk:

{{comic
| number = 2363
| date = September 23, 2020
| title = Message Boards
| image = message_boards.png
| titletext = (c) You can have a scooter when you pay for it yourself, and (d) if you can't learn to start a new thread rather than responding to an old one, you'll be banned. [thread locked by moderator]
}}

==Explanation==
{{incomplete|Created by Julian's kid in 2040, who wants a hover-scooter. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

The joke of this comic lies in the dates of the forum posts and the relation between the posters.

The initial post was made in 2000 by an, at the time, teenaged girl (presumably 15 years old given her username ends in '85), complaining that her mother did not want her to get a vehicle - the reply was written in 2020, twenty years later, by the now-adult woman's son, Julian, who is complaining that, 20 years previously, his mother complained to her mother about something that he is now complaining to his mother about.

In the title text, the parent is apparently a mod on that board now and threatens banning if the kid doesn't learn to post a new thread for stuff like this instead of dredging up dead threads from years ago, a common complaint on message boards, except in this case it seems to be more about hiding her hypocrisy from other users on the board than for the usual reason of letting dead threads stay dead.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[View of the "MopedPro" forum on a message board]
:NIN85 (posted December 5, 2000): So mad that my mom won't let me get a Vespa. I'm old enough for a moped license and they're really not that dangerous.
:JULZ (posted September 23, 2020): At least she's not stopping you from getting an electric scooter you don't even need a license for
:NIN85 (posted September 23, 2020): Okay, Julian, (A) you know we talked about this, and (B) how the heck did you find this thread

:Subtitle: I love that message boards are now old enough for this to happen.

{{comic discussion}}

[[Category:Social networking]]