Wikipedia:Reference desk/Archives/Computing/2023 April 8

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April 8

cat (or copy)

In order to get a 28 GB zip file from a computer running OS X into one running Windows 10, I used split (BSD?) to break it up into bits (which I ferried via an SSD formatted with FAT32). I assumed that use of cat (GNU Coreutils) would be straightforward. That was optimistic, it now seems. cat bigfilea{a..q} > monster.zip doesn't work in Windows, so I used cat bigfilea? > monster.zip instead. This produces a 28 GB file, as expected. But whatever is the default unzipper with Win10 doesn't recognize it as a functional zip file. Is vastness a known problem with the default unzipper (should I install and use a superior alternative?), or could it be that the 17 files were concatenated in the wrong order? If the latter, how can I ensure that the 17 files are concatenated in correct (i.e. alphabetical) order? (Should I perhaps be using Windows' built-in copy?) -- Hoary (talk) 03:58, 8 April 2023 (UTC)

Out of curiosity, why not just use (for example) an exFAT drive to ferry the file over in one piece? In any case, to address your first question: although I don't know if the default Windows unzipper has issues specifically with large files, I do know that it can fail to correctly unzip files that other unzippers can handle fine. Have you tried using 7-Zip to decompress it?

If you're concerned about file integrity, just calculate and compare the hashes of the original and the copied file. Shells-shells (talk) 04:48, 8 April 2023 (UTC)

Thank you, Shells-shells. I didn't use exFAT because ... hmm, I'm not entirely sure I remember correctly, but I think it was because when I read about it I failed to notice that macOS has built-in support for it. (I'm even less accustomed to macOS and Windows than I am to MX Linux, for which my back-up drive is formatted to ext4.) 7-Zip turns out to be able to open the laboriously chopped-up-and-reassembled zip file perfectly well. Thank you for the tips.

Another thing that greatly annoyed me about this Windows machines were the frequent pop-ups attempting to wheedle Mrs Hoary into coughing up some cash for a continuation of McAfee something-or-other; it feels good to have that uninstalled. (But now I suppose I should replace it with something.) -- Hoary (talk) 05:34, 8 April 2023 (UTC)

The non-enterprise editions of Windows 10 include Windows Defender, which is more or less fine. This is active automatically if another antimalware software isn't running. --47.155.46.15 (talk) 00:24, 9 April 2023 (UTC)

This is, shall we say, rather more complicated than just connecting the two systems to the same LAN and copying the file. You can even connect the two systems directly with a cable if they both have Ethernet—all modern Ethernet chips do autonegotiation. Or, you may be able to get USB or Bluetooth to work. You may need to install something on the OS X system to make it talk to Windows file sharing and twiddle some settings but that's it. This is assuming you are physically present with the two systems and can do stuff to them. Things to search: "windows 10 os x file sharing"; "windows 10 os x transfer file"; "connect two computers directly with ethernet cable", etc. if you want to do that. --47.155.46.15 (talk) 00:24, 9 April 2023 (UTC)

Are you using Powershell cat? Since Windows doesn't have a cat.exe, my presumption is you're not using cmd.exe, since that would just produce an error, unless you or someone has done funny stuff with the system. If my presumption is right then you're relying on Powershell's filename globbing and the collation order it uses to sort the resulting glob expansion. This might be what caused your problem: Powershell not sorting the filenames in the same order. In Powershell do ls bigfilea? and it will list all the filenames that glob expression expands to. (Yeah I have a bunch of *nix shell experience. Go ahead and pick my brain if you want more of it shared.) -- 47.155.46.15 (talk) 00:46, 9 April 2023 (UTC)

IP user 47.155 said "You can even connect the two systems directly with a cable if they both have Ethernet—all modern Ethernet chips do autonegotiation" This is incorrect. It is possible to connect two ethernet ports with a single cable, but you will need a special ethernet crossover cable which internally swaps the TX and RX pairs over. Mine is coloured bright pink to make it obviously different. Otherwise you will need a simple ethernet switch or most internet routers have 4 ethernet ports. Autonegotiation just sorts out 10/100/1000 speeds and half/full duplex. And then the fun of file-sharing between Win 10 and OSX...MinorProphet (talk) 02:21, 9 April 2023 (UTC)

Ah, this thing is technically called something different, not "autonegotiation". Medium-dependent interface § Auto MDI-X: Newer routers, hubs and switches (including some 10/100, and all 1-gigabit or 10-gigabit devices in practice) use auto MDI-X for 10/100 Mbit connections to automatically switch to the proper configuration once a cable is connected.

Gigabit and faster Ethernet links over twisted pair cable use all four cable pairs for simultaneous transmission in both directions. For this reason, there are no dedicated transmit and receive pairs, and consequently, crossover cables are never required for 1000BASE-T communication. The physical medium attachment sublayer (PMA) provides identification of each pair and usually continues to work over crossover cables as well, even if the pairs are unusually swapped, crossed, or if the polarity of a pair is unexpectedly inverted. -- 47.155.46.15 (talk) 02:34, 9 April 2023 (UTC)

Thanks for the clarification. MinorProphet (talk) 10:44, 9 April 2023 (UTC)

Improve photo scanned from book or newspaper?

When you scan a photo from a book or newspaper, it shows up as a large number of dots (because that is the way it is printed in a book or newspaper).

Is there software that and smooth this out and make it more like the original photo? Bubba73 ^{You talkin' to me?} 04:06, 8 April 2023 (UTC)

This is very easy in Photoshop Elements (cheaper than PS itself), and probably in similar apps. Just search the web for "how to remove halftone dots in photoshop" or whatever. Shantavira|^{feed me} 08:24, 8 April 2023 (UTC)

Thanks! I have Photoshop Elements but I didn't know about that feature. Bubba73 ^{You talkin' to me?} 15:08, 8 April 2023 (UTC)

I found this, and others. Bubba73 ^{You talkin' to me?} 15:10, 8 April 2023 (UTC)

That article is strange. It reports that scanning the clipping produces the dreaded Moiré effect. Instead, the author loaded the image into Photoshop. How did they do that without scanning it, in which case the Moiré pattern would also have been loaded? The resolution of good scanners is much higher, though, than the printed halftone dots, so mentioning the Moiré effect seems pointless. I think it should be possible to make a 2D wavelet transform of the image, flatten the high-frequency peaks reflecting the dot spacings, and do the inverse transform. For a colour image, it will additionally help to separate the CMYK components and treat each before recombining. I don't know if there is software doing this, but I expect the result to be better than applying a Gaussian blur.  --Lambiam 17:41, 8 April 2023 (UTC)

Yes, and it isn't accurate. Some of the things aren't where it says in Photoshop. I've done one test. I adjusted the Gaussian blur, as it says, which got rid of the dots at 2.2 pixels. But then it said to use the unsharpen mask, which didn't make any difference at all as I slid the slider from left to right. Then I found that the "remove camera shake" does sharpen it. So with the blur and then remove shake, I got a noticeable improvement. I don't know what all of those things you are talking about are. The ones I want to do are not in color. Bubba73 ^{You talkin' to me?} 21:05, 8 April 2023 (UTC)

Now I can't find "Filter > Sharpen > Unsharp Mask" in the current version of Photoshop Elements. Bubba73 ^{You talkin' to me?} 21:13, 8 April 2023 (UTC)

On the second one I tried, the Gaussian blur got rid of the dots, but when I did "shake removal" to sharpen it, it did sharpen it, but it introduced artifacts that made it look worse. Bubba73 ^{You talkin' to me?} 23:00, 8 April 2023 (UTC)