Wikipedia:Reference desk/Archives/Computing/2021 August 21

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August 21

Merge 200 pictures into a long line of pictures

Hi! I would like to know how I can merge 200 pictures into one long picture. I've tried manually with Paint but there's a limit of size. Plus, it's extremely slow to do. Is there any software (free or not) that could do that in a few seconds? Ericdec85 (talk) 11:18, 21 August 2021 (UTC)

You can try imagemagic: convert +append in-*.jpg out.jpg

in-* is a pattern to match the names of your input files that should be sorted by name in the order you want. Else you can list them all by name.

Graeme Bartlett (talk) 12:15, 21 August 2021 (UTC)

The term for what you are doing is image stitching, and we have Comparison of photo stitching software to get you started on considering programs that will do it for you.-gadfium 20:44, 21 August 2021 (UTC)

Upload and download speeds

I have Gigabit Ethernet at home over a fibre optic connection. Speed tests carried out under controlled conditions at different times of day show that although my upload speed approaches 900Mbps, as one would expect, my download speed rarely rises above 20Mbps. As I understand it, Gigabit Ethernet is symmetrical, i.e. upload and download speeds should be more or less the same. The network card and Ethernet cable are both new. Besides, if there were a problem with my hardware, I would have expected it to affect both my upload and download speeds, but it is only my download speed which is slow. The only explanation I can think of is that other people who share my connection are doing a lot of downloading, but it's summer and a lot of people are away on holiday, plus, as I say, the same download speed is observed in the middle of the night. What could be causing the download speed to be so slow? And yes, I will ask my ISP of course, but I wanted to get the opinions of random people on the internet first. --Viennese Waltz 13:32, 21 August 2021 (UTC)

You should address these questions to your internet service provider. Ruslik_Zero 20:39, 21 August 2021 (UTC)

As I have already said, I intend to do so. I want to hear from the experts on this desk what might be causing this. --Viennese Waltz 21:44, 21 August 2021 (UTC)

I don't think you're giving enough information on these "controlled conditions" for any meaningful comment. What remote host/s as being used for the test and how many connections were used? Was this with UDP or TCP. What software was used for this "controlled tests"? Speed tests website running on browsers are known for having problems saturating a gigabit connection. It shouldn't be quite as bad as 20Mbps but still it's better to use their dedicated apps like the one on the Windows 10 store. What sort of computer is this? The fact you mentioned "network card" makes me wonder since many motherboards have had GbE built in for ~15 years. Are you using some dodgy prioritisation drivers or software? Killer NIC software/drivers are known to do totally crap stuff and IMO should be completely uninstalled and replaced with standard drivers for whatever chipset is being used. Nil Einne (talk) 23:50, 21 August 2021 (UTC)

Assume the results of the speed tests are accurate. No, I am not "using some dodgy prioritisation drivers or software". What else could be causing my download speed to be much slower than my upload speed? You tend to be quite a verbose poster, so I'd be grateful if you could limit your response to 200 words or less. Thanks. --Viennese Waltz 15:42, 22 August 2021 (UTC)

Sorry but your question still makes no sense without further info. What do you mean by "accurate"? A single downstream connection from a host behind a dialup modem in Timbuktu when you live in Austria or the UK is a very different thing from the combined speed of 10 downstream connections to multiple major providers (e.g. CDNs) hosted near you with excellent connectivity to your local node. If you regularly get 10Kbit/s to the modem, and 20Mbit/s with the combined, both results are probably accurate. The cause for the first being so much slower than your upload is ultimately the modem. But even if the modem was replaced by a fibre connection, there are multiple things which may reduce the downstream speed from you to the host. The second suggests there's something weird with your connection. But even then, it's still impossible to comment on the cause. You didn't even mention whether you're testing download and upload simultaneously. If you are and you're using TCP, the problem could be saturation of your upstream and poor prioritisation of ack packets. The result is an "accurate" test of what to expect with your hardware under those conditions. Nil Einne (talk) 19:37, 23 August 2021 (UTC)

P.S. Even if the upstream and downstream are tested with the same host, it could be one of those older dialup modem upstream + satellite downstream connections. Point being without info on the host/s it's impossible meaningfully comment on what you results means because we don't know if they can achieve more than 20 Mbit/s nor if your connection to them should be somewhat symmetric in bandwidth. Nil Einne (talk) 19:45, 23 August 2021 (UTC)

P.P.S. This pushes me well over the 200 word limit so maybe it'll be ignored but if at all possible, test don't assume. A good test would be the connection speed between the testing device and some other devices on the router. If there's no other device with at least fast ethernet (fast should allow speeds significantly over 20Mbit/s), then even testing the connection to a recent smartphone over WiFi located near the router may help as you may be able reach 50 Mbit+ even upstream. (Speed to the router could be an option but many domestic routers even with USB 3 ports are terrible NASes.) Nil Einne (talk) 20:07, 23 August 2021 (UTC)

Are you sure you have not reversed upload and download? Often the upload speed is reduced as most residential customers require much more download than upload. Graeme Bartlett (talk) 02:58, 22 August 2021 (UTC)

No, I have not reversed upload and download. I just did another speed test, 18Mbps download, 860Mbps upload. --Viennese Waltz 05:11, 22 August 2021 (UTC)