hpr-knowledge-base/hpr_transcripts/hpr0934.txt

Episode: 934
Title: HPR0934: LiTS 001: qrencode
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0934/hpr0934.mp3
Transcribed: 2025-10-08 05:08:41

---

Welcome to Linux and the Shell Episode 1.
My name is Dan Washco.
I'm your host, and today we are going to talk about the QR Incode application.
But before we do that, let's talk about QR codes or quick response codes.
QR codes were originally developed by the automotive industry.
Or the use of scanning parts.
They developed this because of the limitations of the current scanning codes, primarily
barcodes at the time, were not stored enough that a barcode stores about 20 digits.
But QR codes can store up to 7,089 characters and can handle an array of data, including
alpha, numeric, binary, and kanji, as just opposed to numeric data.
Now how does it do this?
Well, a traditional barcode holds data only on a horizontal plane.
So it can only be read horizontally.
Whereas the QR code is a 2D code and a matrix, which allows data to be read both horizontally
and vertically, therefore allowing for far more data and other features like error correction
into the QR code to be scanned in.
QR code can be read in 360 degrees because it has what is a called a position detection
patterns around it.
Now, if you've ever seen a QR code, they are little squares with a whole lot of almost
like white noise data in them and typically have on the lower left, lower upper right,
and upper left corners, a larger square.
Compared to the rest of the data, really well defined squares.
Those are the position detection patterns there.
And they determine the order which the code could be read.
So no matter what direction the code is read from, the data is always read properly.
Because of this position detection patterns, QR codes can actually be appended inside
one another in a structured format.
So that is another benefit over the standard barcode.
And I had said that QR codes are a square of black and white dots.
And what they are, what those black and white dots are grouped together in what is called
modules.
Now, the number of modules in a QR code is determined by the version of the QR code.
And currently there are 40 versions available with version one containing 21 modules on
the vertical and 21 modules on the horizontal.
Each successive version adds another four modules per side, up to version 40, which contains
177 modules on the vertical and 177 modules on the horizontal.
The higher the version number, the more data that can actually be stored inside the QR code.
In addition to data, there's also error correction levels.
There are four levels labeled L, which is a 7% correction level, approximately M, which
is approximately 15% correction level, Q, which is approximately 25% correction level,
and H, which is approximately 30% correction level.
These levels define the number of blocks assigned in each module for error correction.
The higher the error correction, the less data that can be stored.
But the higher the error correction, the more data that can reliably be read in a situation
where the QR code becomes dirty or damaged.
Now note that this was originally developed by the automotive industry to be used in a factory.
So these QR codes could get easily smudged or damaged.
So therefore, the higher the error correction level, the less data, but the more reliable
it is.
At a level L, the lowest level, are typically used in clean room environments where you
don't really need to worry about data and damage happening to the QR codes.
Levels L, M, and Q are, M is probably pretty standard for just about any use, but Q, if
you were going to print your QR codes and put them up on posters around outside, you might
want to go with Q, because the QR code could get a little dirty outside.
It might get ripped or whatever, but M will suit most purposes.
Q, you could do that if you just want a little more error correction, but H should primarily
be used in a factory environment where it is dirty and damaged could likely occur.
Another factor in QR code is the module size.
Now this determines the size of each individual module in millimeters.
The larger the module size, the more stable and easier it is to read the QR code, but
the larger the actual QR code will be.
So you have to balance module size to use.
Again, something that would want to be printed on printed media, you might want to have a larger
module size as opposed to maybe something you're going to have on your screen.
And finally, there is the margin size.
You can adjust this, but typically the margin size is a four module wide margin around
the symbol.
It's a dead area and that's required that that area exists around the symbol so that the
scanner knows where the code begins and where it ends.
So all those factors into creating a QR code and the amount of data that can be inside
the QR code and the resulting size of the QR code.
At the lowest error correction at the highest module size, you can have a QR code hold up
to 7,089 digits.
There are, if you go to the website, there's links at the bottom that break all this down
off the Denzo wave website and gives you nice grids on how much data can be held at
what version level, at what error correction level.
If you're really that interested in finding it out, more than likely that type of information
is going to far exceed your uses.
Finally, I just want to give a brief mention of something called the micro QR code.
These were developed for use in specialized areas like circuit boards where the amount
of information or data that needs to be held is small, but the QR size has to be really,
really tiny to fit on the circuit board.
One of the differences between a micro QR code and a standard QR code is that there's
only one position detector pattern.
There's a two module wide margin around the QR code and the maximum data capacity is
35 numeric characters and that's at the lowest error correction level and only numeric
characters.
If you get into alpha numeric characters and higher correction levels or binary, the
amount of data that can be stored in them drastically reduces.
That is QR codes in a nutshell.
There's a lot of information there and more than likely you are not going to require
that to just start generating your QR codes.
Thankfully, QR in code makes it incredibly easy to just dump out whatever it is that you
want to do.
Now, some practical uses for a QR code would be to embed a URL to a website or a video
file into a QR code so that somebody with a smartphone that has a camera could scan
that image in with their camera using a barcode application and it would pop up and ask
them, what would you like to take this information and go to website if it's a website or if
it's a video, would you like to open it on the website or would you like to open it in
YouTube or the video application on the phone?
If it's a text document, you can actually scan in some text in there.
It might ask you if you want to open it in a text editor or a text viewer.
You could also encode vCard information into a QR code.
When you scan it, it would pop up that information of the vCard and allow it to be entered into
the contact information onto the phone.
So while there are a myriad of uses and you're left to your own devices to figure that out,
QR encode, again, makes it really simple to generate whatever you want to do.
QR encode takes some options and whatever string you want to encode.
Now the required option you must pass to QR encode is the dash O option, which is the
output file name.
QR encode generates PNG files and the dash O is going to be whatever the file name is
going.
You want it to be .png and it will output it whatever string that you pass to it.
So for example, if I wanted to create a QR code of the website packerpublicmedia.org,
I would just simply type QR code, space dash O, space, hpr.png, http, colon slash slash
hackerpublicradio.org, and it would create a nice little QR code with the standard defaults.
QR encode does a great job of determining what module version level to use.
By default, it uses an error correction level L, which is approximately 7%.
Now recall, that is for a clean room environment.
And if you're going to be using this to show on a website, chances are that that's good
enough.
But if you wanted to do the uses on printed media, you might want to go into m or q.
So be aware of that.
It also does a good job of handling the margin width and the module size.
Generally, you won't have to go in and manipulate any of that information.
But if you wanted to, you could very easily handle that by passing different options to it.
For instance, if you wanted to set the symbol version number, that's what the dash v option.
And again, this level is 1 through 40 error correction level is the dash L option standard
to 72 dpi.
It's good for screen, but you can adjust that with the dash d to create something like 300 dots
per inch for code that needs to be printed.
Then there's also pixel size for the screen by default.
It's three, but you can set that with the option dash s.
And finally, margin width, that's the dash m option.
And by default, it is four pixels.
But otherwise, taking the standard defaults of QR encode will probably produce a QR code
to suit your needs right out of the box.
And remember, the more data that you're going to put into the QR code, the larger it is
going to be, the resulting code will be.
So be aware of that.
Most of the time, you can just pass a string in there and it will create a QR code based
on that string.
But I had mentioned that you could put v card information in there.
The way to get v card information, or let's say any kind of text file if you had a poem
that you wanted to put into a QR code, is quite simple.
And you wouldn't want to type it all out on the command line, although you could, you'd
want to create that into a file beforehand, a text file, and then redirect that file
as standard in, as opposed to typing information out onto the command line, to the QR encode
application.
Kind of like we discussed last week with on the redirection.
So it would be QR encode space dash out would be some file, let's say, Dan's address.
And space less than symbol and the v card information, my address, when you do that,
it will create a v card QR code that all the information in the QR code is my v card.
So if somebody were to scan that with a phone, it would ask if I wanted to input that into
their phone as a address or a contact.
So it's pretty handy.
I hope that this episode has given you a little taste of QR codes and start the juices
flowing as to where you could use these and what you could use these for, and you'd
be interested in trying out the QR encode application.
Head on over to the website linuxintheschel.org and check out entry number one for the full
write up and all the links to the documentation and standards for QR codes and the examples
over there, watch the video.
It's fun stuff and you can produce some really neat QR codes to do love letters or whatever
you want to.
The sky's the limit with these things.
So check it out.
Thank you very much for listening and we'll see you in another fortnight.
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