Using MTF, how can I discover the smallest detail a smartphone camera can resolve for use in generating QR codes?

Since most camera lens combinations have variable MTF across the field (that is, the system can usually resolve finer details in the center of the frame than on the edges and in the corners), there is no single “magic number”, even for a specific camera/lens combo.

Then there’s the variability introduced by low light/high ISO that reduces the amount of detail that the same system can resolve compared to when that system is used under more ideal conditions.

There’s also the fact that most scans will not be made with the phone perfectly aligned with the QR code. So the minimum theoretically possible size under “perfect” conditions with the target framed perfectly level by the phone and perfectly perpendicular to the phone’s sensor won’t work if the phone is tilted and/or rotated several degrees with respect to the target QR code.

In the end you have to “aim low” if you want to create QR codes that can be compatible with a large majority of phones.

As for the QR codes themselves, the major variables are:

  • Scanning distance. A QR code on a billboard that will be scanned from 40-50 feet needs to be quite a bit larger than a QR code on a business card that will be scanned from about 12 inches.
  • The amount of data encoded. The more data you want to encode, the more discrete squares called data units arranged in rows and columns your QR code will need, and the larger it must be for each row and column to be the same size. A 25×25 QR code with 625 data units can be smaller than a 125×125 QR code with 2132 data units.
  • The design features of your QR code. If you want to make it something other than a plain B&W “bar code” looking QR code, you need to include plenty of error correction (which increases the total data needed to communicate the same amount of information). QR codes that have colors or are embedded in an image attract more scans than plain B&W QR codes do.
  • Printing considerations. Since printers often scale images, using vector graphics is usually best for QR codes. There also needs to be good contrast between the QR code and the background upon which it is printed.

There are a variety of resources on the net that address this. Here are four that are helpful:

QR Code Minimum Size: Calculate ideal size for your use case
What Size Should a QR Code Be in Relation to Scan Distance?
What is the ideal print size of a QR Code?
QR Code Minimum Size: How Small Can a QR Code Be?

Discover smallest resolvable detail of smartphone camera with MTF

Given a chart I created myself, resembling e-sfr charts, a smartphone and a MTF plot, how could I discover the smallest resolvable detail, dimension wise ? The problem with smartphones is that we don’t always have all of the technical hardware information.

To give more context, I’d like to create the smallest QR code that could be read by a smartphone camera when printed. Mine in the occurrence is the Xiaomi MI 9 SE, however, I’d like it to work with any.

Discover where a list is referenced

I am using sharepoint 365.

The cliente need to delete one list.

He is not sure if any other list uses the list that will be deleted.

Is there a way to discover if the list is referenced into another areas of sharepoint?

Thank´s in advance

Best way to discover creating events in calendar application

I have a mobile calendar app

First I want to say that my app is not a normal calendar app, because users may sometimes need to add a lot of events at once, not like google calendar where people usually create one event every time they need, so I need a UI/UX that will make creating a lot of events at once easy and fast.


The user can press the ‘plus’ button in the top left corner, to toggle Adding Mode.

In Adding Mode, single-tapping a date opens the “New Event Screen”.

But the user can also show the same “New Event Screen” by long-pressing a date, without being in Adding Mode.

  1. What is the best way to indicate that long-pressing a date is also a possible way to add events? I find creating events by long-pressing way quicker than pressing the plus button and then single-tapping a date, especially if the user wants to create a lot of events at once.
  2. Should I remove single-tap “Adding Mode” and instead only creating events with long-press? Because if I’ll keep both ways to create events I worry it might be confusing for the user which way to choose.
  3. Is long-press a good gesture for this kind of thing?

Any other advice will be appreciated!

how to discover if a Samsung device is already registered with Knox Mobile Enrollment (KME)?

I’m asking this question as a end user not a Knox cloud admin. Bearing this in mind,

I’ve finished the first initial setup without allowing the device to connect to the Internet (and thus couldn’t be aware of any possible Knox enrollment prompt). And now I would like to discover if this device is already registered with Samsung Knox Mobile Enrollment (KME) and thus if it is a corporate-owned device or BYOD (any kinda work device)?

I shouldn’t do a factory reset for some reasons. How to verify that without giving the device a factory reset?

virtualization – Unable to discover other networks using Airodump-ng in Kali VirtualBox (Beginner)

first post. I have an ALFA AWUS036NH network adapter I am trying to use in Kali VirtualBox but when I run “sudo airodump-ng wlan0mon” it scans for networks but does not come back with any results. I ran airmon-ng check kill and killed 1 process- 1181 wpa_supplicant. Then I typed “sudo airmon-ng start wlan0” to switch to monitor mode. From here I try to discover other networks with “sudo airodump-ng wlan0mon” but it keeps cycling through channels and not displaying any results, or error messages. Can anyone point me in the right direction? Thanks

legal – UK car rental: protections against charges for damage, that was pre-existing and renter had no chance to discover at checkout?

Are there any consumer protection laws/regulations against such charges, in the UK?

The legal aspects are probably a better fit law.stackexchange.com

Chances are, the legal path would be difficult. Read your contract carefully: when you checked out the car you probably signed a statement that you have indeed inspected the car and that you will take full responsibility for any damages or “changes” that occur while you are using the vehicle. These clauses are their for a reason: rental companies hear “oh, that wasn’t me” ten times a day.

If it’s a reputable company (Avis, Hertz, Enterprise, Europcar, Alamo, Sixt, etc. ) you can probably negotiate your way out of there. Some of the field agents can be overzealous and that just annoys customers and results in bad reviews on tripadvisor and social media.

It’s a classical case of “your word against theirs” so you need to establish credibility. Call them up or write. Be polite, reasonable, constructive but firm. Explain what happened and ask for advice on how to proceed. Carefully choose your sentences. “The alleged damage wasn’t even visible to the naked eye”, “Lighting conditions during check out made it impossible to see the damage”, etc. Express that you would be very disappointed with the company, if they were to force you to pay for damage that you didn’t do.

ubuntu – my laptop can’t discover bluetooth devices neither be discoverable

I’ve just installed Ubuntu 20.04 and Bluetooth is working fine but when I try to discover my phone my laptop can’t find any device and I tried discovering my laptop in my phone but can’t either find my laptop. and then I find some posts that tells to check the software and updates setting for drivers and so but found only one driver :

Software and updates settings Bluetooth settings
Bluetooth Adapter

and I can’t find any solution to fix this problem ,can anyone suggest some solutions to me , I am a new Ubuntu user so I can’t fully comprehend what to do

peer discovery – How long on average would it take to discover all other nodes in Bitcoin network and connect to them? Are there technical obstacles to this?

discover all other nodes in Bitcoin network and connect to them

Discovery and connecting are a bit different. To discover a node that node has to have advertised itself using an addr message. I believe nodes that don’t accept incoming connections (have no listening port) don’t do this, so they can not be discovered unless your node listens for incoming connections and they initiate the connection.

Connecting to known nodes is simple and is what statistic tools such as bitnodes do, an I’m assuming this is what you have in mind otherwise as @RedGrittyBrick there is no point.

It could start from initial peer discovery using DNS seeders then it is a matter of making a TCP connection to each node’s IP address through the port they listen on (almost always the default 8333 and 18333 for mainnet and testnet) and performing the handshake (version+verack) which doesn’t take more than a second. A getaddr message could be sent to each node asking for a list of nodes they know of to construct a list and connect to each of them.
I don’t think going through all reachable nodes (about 10k) would take longer than a minute.

Discover Who Owns Any Cell

Phone Number Just 2 Minutes From Now! I Know You Have Been Curious About Who Owns That Cell Number That Keep Calling You Or Your Spouse,  Business Telephone Lists   So Find Out Now! Locate The A Reverse Lookup by a Phone Number Database Will Trace Any Phone Number Instantly e two various types of opposite query by telephone number information bases accessible. The first are the free administrations.  Business Telephone Lists   A simple method to depict the free converse telephone number look into administrations is that it will give you a similar data that is accessible in the overall white pages. The free administrations may persuade they will give all of you the data of the paid administrations, Business Telephone Lists    yet as a general rule, after you enter the telephone number you are searching for, they will at that point reveal to you the data is accessible, however a charge is needed to get to it. Business Telephone Lists    The free administrations simply give data that is as of now accessible to the general population.