Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Thomas Schmitt]

Hi,

Max Nikulin wrote:
> I admit "dithering" may be incorrect term, [...]
> Consider 2 squares having size of 2.5×2.5 pixels. Non-even sizes and fuzzy
> lines variants:
> █████
> ██████
> ████ ██
>██ ██
>█████
> Second variant might have sense if an image is treated as a photo unlikely
> having regular patterns with horizontal and vertical lines.

I see ...
The second rendering style is probably best described as "Bad Distortion".


Have a nice day :)

Thomas

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 20/03/2024 01:51, Thomas Schmitt wrote:

Max Nikulin wrote:

When vector graphics, that does not match device resolution, is rasterized,
the result is either non-even sizes of similar elements or fuzzy lines due
to dithering.


Nitpicking:

"Dithering" in raster graphics is emulation of color resolution at the
expense of space resolution.

[...]


The fuzzy lines are rather the opposite. They use surplus color
resolution to emulate ibetter spacial resolution. Over here the usual
term is "Anti-aliasing".


I admit "dithering" may be incorrect term, but I am in doubts if that 
printer (claimed to have 300dpi resolution, but not suitable for QR 
codes) has surplus color resolution. I do not mean anti-aliasing in the 
sense of adjusting pixels darkness (and color).


Consider 2 squares having size of 2.5×2.5 pixels. Non-even sizes and 
fuzzy lines variants:


█████
██████
████ ██
   ██ ██
   █████

Second variant might have sense if an image is treated as a photo 
unlikely having regular patterns with horizontal and vertical lines.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Thomas Schmitt]

Hi,

Max Nikulin wrote:
> When vector graphics, that does not match device resolution, is rasterized,
> the result is either non-even sizes of similar elements or fuzzy lines due
> to dithering.

Nitpicking:

"Dithering" in raster graphics is emulation of color resolution at the
expense of space resolution. Multiple coarsly colored pixels together
create the impression of a finer color tone. A certain random aspect is
added to prevent unwanted patters.
  https://en.wikipedia.org/wiki/Dither

The fuzzy lines are rather the opposite. They use surplus color
resolution to emulate ibetter spacial resolution. Over here the usual
term is "Anti-aliasing".
  https://en.wikipedia.org/wiki/Line_drawing_algorithm
  https://www.geeksforgeeks.org/antialiasing/
I get a suspiciously high share of german language results when
searching this term in the web. But "Computer Grapics" by Foley, Van Dam,
Feiner, Hughes of 1990 has a dozen occurences in its Index.


Have a nice day :)

Thomas

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 13/03/2024 12:25, hw wrote:

On Mon, 2024-03-11 at 23:45 +0700, Max Nikulin wrote:

It seems you expect some number that you can use for any QR code. There
is no size that fits for all codes.


It's because you said: "I believed that 300dpi is high enough
resolution for QR-codes of reasonable size if source image has proper
quality." that I keep asking what you consider a reasonable size.


QR codes with more modules must be printed at larger size. Isn't it obvious?

By the way, is 300dpi real resolution of your printer or it is 
over-resolution achieved with overstrike with some offset? If so, does 
the printer driver take it into account?



Out of curiosity I tried to scan a QR code printed on a thermal printer
(so likely having ~200dpi resolution) having size of approximately 0.8in
and 50 pixels (modules) per inch. It encodes a 69 bytes long link.


Did you successfully scan it?


Instantly, no trouble at all.


It limits amount of information you may put into QR codes. You can still
choose to use e.g. 4,5,6, etc. printer dots per QR code module.


How can I choose that?  I don't know that there would be an option
with pdflatex or pdf or the printer driver that would let me choose
how many dots per module the printer puts onto the label.


When a code is generated you can look at it and count its modules. The 
next step is simple math. You have resolution, dots per module and 
number of modules, so you can get size and rerun LaTeX.



When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
Perhaps the pst-barcode package uses vector graphics?


Nice, however you have to adjust size to avoid blurring.


How do you mean?  I thought vector graphics don't blur when scaled.


When vector graphics, that does not match device resolution, is 
rasterized, the result is either non-even sizes of similar elements or 
fuzzy lines due to dithering.


If a few multiplications and divisions is so hard problem and each QR 
code module occupy at least 3x3=9 printer dots then I would try to 
rotate the code by e.g. 30 or 45 degrees before printing.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 14/3/24 17:47, jeremy ardley wrote:
For reference on a 203 DPI (8 dots per mm) printer, a GS1-128 barcode 
takes up 12 modules per character. The minimum size of a module is 1 
pixel so 1 character is 12 pixels wide or 1.2mm on a 203 dpi printer.


Assuming a 40 character barcode at 1 pixel per module, it will span 48mm.

However it is very unusual to have 1 pixel per module. Instead at 2 
pixels per module the barcode is 96mm and at 3 pixels it will be 144mm



My error; The character spacing is 1.5mm at 203dpi. So 40 characters is 
60mm at 1 pixel per module, 120mm at 2 pixels per module, and 180mm at 3 
pixels per module. This means for a 40 character barcode you can at best 
print at 2 pixels per module on a typical 100x150m shipping label. This 
allows for no errors in quantization of pixel sizes and It's really hard 
to do with a printing system that does not start and continue with 
accurate pixel registration.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 14/3/24 06:59, hw wrote:

Manufacturers can provide CUPS drivers as well, but the barcode
application is usually only windows.

In my case I had to write my own CUPS driver as the manufacturer does
not provide one.

How did you do that?


It is simply a C program that gets given some parameters and a bitmap by 
CUPS


The program processes the bitmap and frames it with printer commands to 
place the bitmap on the printer page.


CUPS abstracts the actual device interface (in my case USB). But in 
development I wrote the code to send commands directly to the USB device





Getting back to pixel registration, the latex CUPS route is very
unlikely to work well.

It's working great here since years.  Barcodes are no problem, only qr
codes can't be scanned.



This surprises me greatly. 2D codes have very large features compared to 
barcodes. They should be relatively immune to pixel quantization.


For reference on a 203 DPI (8 dots per mm) printer, a GS1-128 barcode 
takes up 12 modules per character. The minimum size of a module is 1 
pixel so 1 character is 12 pixels wide or 1.2mm on a 203 dpi printer.


Assuming a 40 character barcode at 1 pixel per module, it will span 48mm.

However it is very unusual to have 1 pixel per module. Instead at 2 
pixels per module the barcode is 96mm and at 3 pixels it will be 144mm


With the barcode you have no leeway in the pixel sizes. You must have it 
exact to scan.


In comparison, a QR code typically will have modules 8 pixels square and 
typically is 26x26 or 32x32 pixels. At 26x26  the printed code is 26mm 
square at 203dpi. You can afford to be out by a pixel at those dimensions.


If you have problems scanning QR codes at those sizes perhaps your QR 
codes are invalid to start with? If you print them out really large will 
they scan?

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Wed, 2024-03-13 at 03:50 +0800, jeremy ardley wrote:
> On 12/3/24 21:21, hw wrote:
> > 
> > Even if they did that, it would be totally useless because it won't be
> > able to automatically print labels from databases.
> 
> The manufacturer applications  usually allow you to print a list from a 
> spreadsheet or text file.

That isn't very useful.

> > > It is possible to use document generation tools like latex and printing
> > > systems like CUPS to print a label, but pixel registration will be poor.
> > Why?  The manufacturer provided a CPUS printer driver without which
> > printing wouldn't be possible at all.
> 
> Most custom barcodes programs run on windows and don't use CUPS.

That makes them entirely useless.

> Manufacturers can provide CUPS drivers as well, but the barcode 
> application is usually only windows.
> 
> In my case I had to write my own CUPS driver as the manufacturer does 
> not provide one.

How did you do that?

> Getting back to pixel registration, the latex CUPS route is very 
> unlikely to work well.

It's working great here since years.  Barcodes are no problem, only qr
codes can't be scanned.



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 13/03/2024 02:50, jeremy ardley wrote:
Getting back to pixel registration, the latex CUPS route is very 
unlikely to work well.


TeX with MetaFont fonts worked well with low resolution dot matrix 
printers. Rasterized fonts may be generated for specified resolution. It 
should be still possible unless wide Unicode coverage is required.


I may be wrong, but I have impression that better support of modern 
vector fonts (TTF, OTF, etc.) in LuaTeX has other side. HurfBuz font 
library with priority to speed can not align characters to specified 
pixel grid. Likely nobody cares concerning font hints for low resolution 
devices.


Scale and position of images like QR codes should be adjusted to printer 
resolution.


More than a decade ago it was necessary to provide a document for 
archival purposes. I got a couple of complains: font with too thin lines 
and gray rather than black toner. The cartridge was refilled almost a 
dozen of times, but for routine documents quality was still good. 
CM-Super Type 1 font (converted from original Computer Modern with 
additions related to more scripts) really has hairlines. I configured 
metafont to increase minimal line width and generated a document with 
600dpi raster fonts using latex+dvips+ps2pdf instead of pdflatex. I went 
to a print shop nearby with hope to find there a printer filled with 
really black toner. The person there did not get the point why I was not 
satisfied looking into a test page from my document. It was blurry. 
Likely the page was scaled to printable area and dithering was applied. 
I preferred to go to another shop and got a stack of paper printed with 
proper quality. Either stuff there were a bit more experienced or 
default printer settings were more reasonable.


So it is not difficult to ruin efforts invested into print quality by 
inappropriate checkbox. The process is not fool-proof.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Florent Rougon]

Florent Rougon  wrote:

>   - printer matrix alignment if printer resolution is low (more
> difficult; maybe try with some very small horizontal and veritical
> shifts to see if it helps...).

Thinking about it more, this is probably hopeless unless printer
resolution is *extremely* low. Typical printer dots are so small that
you can't realistically expect paper placement to have good enough
precision to align both grids (say, 1/4 of the printer dot size).

This is, I believe, what Jeremy meant when he wrote earlier in this
thread:

> Getting back to pixel registration, the latex CUPS route is very unlikely to
> work well. However a custom application that generates a pixel perfect bitmap
> that is printed at 100% scale through cups should work.

I agree with that if printer resolution is so low that the QR code and
printer dot grids have to be aligned. Even with perfect size in the PDF,
there is very little hope that paper will be every time correctly
aligned in the vertical and horizontal directions with the matrix of
dots managed by the printer—a dot at 300 dpi being approximately
0.08 mm. The only realistic hopes are:
  - high enough resolution that grid alignment doesn't really matter (is
300 dpi enough? Maybe.);
  - direct control over the printer bitmap (what Jeremy mentioned).

For the sake of completeness, the following LaTeX document (an inline
attachment) draws a QR code whose modules are correctly placed for some
“ideal” 300 dpi printer. This assumes that printer dots perfectly start
at a dot-size multiple from the top left corner of the physical page,
which probably can't be obtained in practice. So, this is mainly to show
how accurate placement and computations can be done (\fpeval is provided
by xfp; it is very accurate and expandable).

\documentclass{article}
\usepackage[papersize={50mm,35mm},margin=0cm]{geometry}
\usepackage{xfp}
\usepackage{qrcode}

\pagestyle{empty}
\newlength{\modulesize}
\setlength{\modulesize}{\fpeval{6/300}in}% assume 300 dpi, set 6 dots/module

\begin{document}

\noindent
\hspace{10\modulesize}% horizontal offset from paper edge: 10 modules
\raisebox{\dimexpr \topskip - \height - 10\modulesize}{% ditto in vert. direction
  \qrcode[height=25\modulesize, version=2]{Hey Debian-user!}}%
% The modules will have the expected size only if the QR code is effectively
% doable at version=2 (check the LaTeX terminal output). Indeed, version=2
% means 25×25 modules.

\end{document}

Regards

-- 
Florent

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Florent Rougon]

hw  wrote:

>> That is quite likely: the pst- prefix means this is PSTricks, which is
>> an oldish way of doing vector graphics with LaTeX. I tend to avoid
>> PSTricks these days as it is generally awkward to use in PDF contexts,
>> although there are various workarounds that often allow to do so.
>
> Is that bad?  It works great for what I'm doing.

Well, “bad” is a strong word in this context. ;-) First, PDF has been
replacing PostScript in the last 20+ years, so it is often easier to
find tools that do interesting things with PDF than with PostScript.

Second, regarding the existing workarounds that allow PSTricks code to
be used in PDF workflows: I haven't used many of them but AFAIK, most of
the times, if you want things to work automatically, you need to enable
\write18 which has security implications. In the most relaxed case, it
allows the compiled document, as well as any class or package it loads,
to run arbitrary shell commands. There is a restricted mode for \write18
(see -shell-restricted and “§5.5 Shell escapes” in `texdoc web2c`), but
it currently doesn't allow running ps2pdf:

,[ /usr/share/texmf/web2c/texmf.cnf ]
| shell_escape_commands = \
| bibtex,bibtex8,\
| extractbb,\
| gregorio,\
| kpsewhich,\
| makeindex,\
| memoize-extract.pl,\
| memoize-extract.py,\
| repstopdf,\
| r-mpost,\
| texosquery-jre8,\
| 
| % we'd like to allow:
| % dvips - but external commands can be executed, need at least -R1.
| % epspdf, ps2pdf, pstopdf - need to respect openout_any,
| %   and gs -dSAFER must be used and check for shell injection with filenames.
| ...
`

One of the problems with PostScript is that it is “too powerful” for
something that should only produce text and graphics—AIUI, security
concerns were not at the core of its design.

Finally, for a few things like transparency and “new” font formats
(e.g., TrueType, OpenType), PostScript is either a no-go or has
solutions that appeared very late, contrary to PDF.

>> The ubiquitous, powerful and modern way to do vector graphics in LaTeX
>> is PGF/TiKZ[1],
>
> That package has almost 1300 pages of documentation which doesn't seem
> to mention qr-codes or barcodes.

Right. Presumably, the qrcode package is good enough. BTW, since its
\qrcode command produces a TeX box without using any TikZ code, it can
be placed without restriction in a TikZ node (I say this because TikZ
nodes can't be nested—more precisely, doing so is not supported).

> I wonder why it uses different options for URLs and other data.  What
> difference does that make?

I believe you misunderstood the manual here, or maybe I don't understand
what you meant. The \qrcode command can encode both URLs and other text.
What I see is simply options (and the starred variant \qrcode*) to
decide whether to turn the QR codes into PDF hyperlinks.

Global switch at \usepackage level:  hyperlinks/nolinks
Local switch for each \qrcode command:   link/nolink

\qrcode*{…} == \qrcode[nolink]{…}

These options are provided because when the hyperref package is loaded,
QR codes are output as hyperlinks by default; however, it is quite
possible to write QR codes that don't encode URLs, in which case making
them hyperlinks would be confusing and useless.

> It might be worth a try for when I need to experiment with qr-codes on
> small labels again.  It might not work because I may need to place the
> qr-code in some way and it could conflict with other packages like the
> labels package ...  I even might have already tried it; it's been a
> few years and I don't remember exactly.

Since \qrcode outputs a TeX box without using any TikZ code, it has
about the highest level of “compatibility” you can expect in a TeX
document.

> Now I'm wondering why the qr-codes I printed with the label printer
> couldn't be reliably scanned.  When I look at [1] and [2], for the
> data I wanted to print (between 38 and 40 alphanumericals at L
> quality) I would have to use a version 2 qr code, i. e. 25x25 modules.
> I don't know how the modules transfer to dots, but assuming the
> minimum of 4 dots per module, it would take 25 x 4 dots, i. e. 100
> dots.  Each module would be 0.33mm in size which would require 25 x
> 0.33mm, i. e. 8.25mm for the size of the qr-code.
>
> I printed the qr-code much larger than that, about 1x1".  That is
> about three times as large as would be required, and the printer can
> print three times as many dots per inch as the 100 dots needed.
>
> So in theory, my theory that the resolution of the printer is too low
> can't be true.
>
> But why couldn't these qr-codes be scanned?  It shouldn't have been a
> problem at all.

L quality is the worst; can't you use a better one? Also worth
considering:

  - scanner limitation? Did you try to scan the codes with a smartphone?

  - printer matrix alignment if printer resolution is low (more
difficult; maybe try with some very small horizontal and veritical
shifts to see if it helps...).

Regards

-- 
Florent

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Mon, 2024-03-11 at 23:45 +0700, Max Nikulin wrote:
> On 11/03/2024 08:06, hw wrote:
> > On Sun, 2024-03-10 at 09:50 +0700, Max Nikulin wrote:
> > > On 10/03/2024 04:41, hw wrote:
> > > > \psbarcode{textblah foo}{height=0.6 width=0.6 eclevel=L}{qrcode}
> > > > 
> > > > That works for 600dpi laser printers.  When you print the QR-code with
> > > > a 300dpi label printer you can't reliably scan it, not even when you
> > > > make the QR-code 1x1" in size.
> > > > 
> > > > Perhaps that's not a reasonable size?
> > > 
> > > Perhaps height and width are chosen improperly. An image some percents
> > > smaller may be sharper.
> > 
> > What size do you consider reasonable?
> 
> It seems you expect some number that you can use for any QR code. There 
> is no size that fits for all codes.

It's because you said: "I believed that 300dpi is high enough
resolution for QR-codes of reasonable size if source image has proper
quality." that I keep asking what you consider a reasonable size.

> Out of curiosity I tried to scan a QR code printed on a thermal printer 
> (so likely having ~200dpi resolution) having size of approximately 0.8in 
> and 50 pixels (modules) per inch. It encodes a 69 bytes long link. 
> Likely the same code scaled to 0.4in will still work, but I would prefer 
> to avoid it, 0.6in should be more reliable. On your 300dpi printer this 
> particular QR code may be printed e.g. at ~(0.8/1.5)in.

Did you successfully scan it?

> > [...]
> > The QR-code must fit on the label, plus some text.  The labels are
> > 50x35mm in size.
> 
> It limits amount of information you may put into QR codes. You can still 
> choose to use e.g. 4,5,6, etc. printer dots per QR code module.

How can I choose that?  I don't know that there would be an option
with pdflatex or pdf or the printer driver that would let me choose
how many dots per module the printer puts onto the label.

> > When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
> > Perhaps the pst-barcode package uses vector graphics?
> 
> Nice, however you have to adjust size to avoid blurring.

How do you mean?  I thought vector graphics don't blur when scaled.



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Mon, 2024-03-11 at 11:58 +0100, Florent Rougon wrote:
> Hi,
> 
> I haven't read the whole thread (sorry) but thought this might help.
> 
> hw  wrote:
> 
> > When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
> > Perhaps the pst-barcode package uses vector graphics?
> 
> That is quite likely: the pst- prefix means this is PSTricks, which is
> an oldish way of doing vector graphics with LaTeX. I tend to avoid
> PSTricks these days as it is generally awkward to use in PDF contexts,
> although there are various workarounds that often allow to do so.

Is that bad?  It works great for what I'm doing.

> The ubiquitous, powerful and modern way to do vector graphics in LaTeX
> is PGF/TiKZ[1],

That package has almost 1300 pages of documentation which doesn't seem
to mention qr-codes or barcodes.

> however this is not even necessary for QR codes, because
> [...]

good :)

> I've played with a different package for producing QR codes in LaTeX,
> which uses the aforementioned \hrule and \vrule primitives: qrcode. Its
> manual is here (follow the “Package documentation” link):
> 
>   https://ctan.org/pkg/qrcode

I wonder why it uses different options for URLs and other data.  What
difference does that make?

> Here is a simple example you can compile with pdflatex:
> 
> \documentclass{article}
> \usepackage{qrcode}
> 
> \pagestyle{empty}
> 
> \begin{document}
> 
> \noindent
> % \qrset affects \qrcode commands in the current group. You can use it
> % to factor out options used for several QR codes.
> \qrset{nolinks, padding}% add padding to make sure the codes are 
> “legal”/readable
> \qrcode[version=1]{Hey Debian-user!}% Can't do version=1 with level=M or more
> \qrcode[level=L, version=1]{Hey Debian-user!}% Less redundancy but is doable
> 
> \end{document}
> 
> Note the terminal output:
> 
> 
> 
>  Version increased to '2' to fit text.>
> 
> 
>  calculated.>
> 
> 
> 
> 
>  calculated.>
> 

It might be worth a try for when I need to experiment with qr-codes on
small labels again.  It might not work because I may need to place the
qr-code in some way and it could conflict with other packages like the
labels package ...  I even might have already tried it; it's been a
few years and I don't remember exactly.

> [...]
> But with low printer resolution constraints, who knows?).
> 
> Hope this helps!

Yes, thanks, knowing about these packages can be useful.

Now I'm wondering why the qr-codes I printed with the label printer
couldn't be reliably scanned.  When I look at [1] and [2], for the
data I wanted to print (between 38 and 40 alphanumericals at L
quality) I would have to use a version 2 qr code, i. e. 25x25 modules.
I don't know how the modules transfer to dots, but assuming the
minimum of 4 dots per module, it would take 25 x 4 dots, i. e. 100
dots.  Each module would be 0.33mm in size which would require 25 x
0.33mm, i. e. 8.25mm for the size of the qr-code.

I printed the qr-code much larger than that, about 1x1".  That is
about three times as large as would be required, and the printer can
print three times as many dots per inch as the 100 dots needed.

So in theory, my theory that the resolution of the printer is too low
can't be true.

But why couldn't these qr-codes be scanned?  It shouldn't have been a
problem at all.


[1]: https://www.qrcode.com/en/about/version.html
[2]: https://www.qrcode.com/en/howto/cell.html

> 
> Regards
> 
> [1] https://ctan.org/pkg/pgf
> 





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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 12/3/24 21:21, hw wrote:


Even if they did that, it would be totally useless because it won't be
able to automatically print labels from databases.


The manufacturer applications  usually allow you to print a list from a 
spreadsheet or text file.



It is possible to use document generation tools like latex and printing
systems like CUPS to print a label, but pixel registration will be poor.

Why?  The manufacturer provided a CPUS printer driver without which
printing wouldn't be possible at all.


Most custom barcodes programs run on windows and don't use CUPS.

Manufacturers can provide CUPS drivers as well, but the barcode 
application is usually only windows.


In my case I had to write my own CUPS driver as the manufacturer does 
not provide one.


Getting back to pixel registration, the latex CUPS route is very 
unlikely to work well. However a custom application that generates a 
pixel perfect bitmap that is printed at 100% scale through cups should work.


There are a number of programs that can do that, though I have not used 
them so far.


- zint

- GNU barcode

- BWIPP

also a possibility is

- qrencode

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Mon, 2024-03-11 at 09:57 +0800, jeremy ardley wrote:
> On 11/3/24 07:34, hw wrote:
> > Do you think that thermal transfer printers with 203dpi would be
> > better suited to print QR codes than the 300dpi multi-mode printers?
> > 
> > I'm not fond of thermal transfer at all.  Usually what is being
> > printed that way fades rather quickly over time and is more slightly
> > gray rather than black and so thin that it's hard to read even when
> > freshly printed.  Perhaps better labels are available, but the labels
> > must not get too expensive ...
> 
> 
> Thermal transfer and thermal direct printers have the same resolution.
> 
> Thermal transfer printers are used for archival labels as they fade very 
> little over time.
> 
> Direct thermal printers are intended for mailing applications where it 
> doesn't matter if they fade after a few months.
> 
> Given that, I think a lot of commercial shippers use thermal transfer 
> for mailing labels. Very few shippers use laser printed adhesive address 
> label, nor non-adhesive in pockets or pouches.
> 
> To print a QR code or other 2D code on any thermal printer, the printer 
> manufacturer will supply an application that generate the codes and 
> prints them independently of the host printing system. These codes will 
> scan perfectly.

Even if they did that, it would be totally useless because it won't be
able to automatically print labels from databases.

> It is possible to use document generation tools like latex and printing 
> systems like CUPS to print a label, but pixel registration will be poor. 

Why?  The manufacturer provided a CPUS printer driver without which
printing wouldn't be possible at all.

> The only practical option for this route is to print the code BIG
 
That's what I thought, but then the codes won't fit on the labels.
That's why I wonder if there's a better way.



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 11/03/2024 08:06, hw wrote:

On Sun, 2024-03-10 at 09:50 +0700, Max Nikulin wrote:

On 10/03/2024 04:41, hw wrote:

\psbarcode{textblah foo}{height=0.6 width=0.6 eclevel=L}{qrcode}

That works for 600dpi laser printers.  When you print the QR-code with
a 300dpi label printer you can't reliably scan it, not even when you
make the QR-code 1x1" in size.

Perhaps that's not a reasonable size?


Perhaps height and width are chosen improperly. An image some percents
smaller may be sharper.


What size do you consider reasonable?


It seems you expect some number that you can use for any QR code. There 
is no size that fits for all codes.


Out of curiosity I tried to scan a QR code printed on a thermal printer 
(so likely having ~200dpi resolution) having size of approximately 0.8in 
and 50 pixels (modules) per inch. It encodes a 69 bytes long link. 
Likely the same code scaled to 0.4in will still work, but I would prefer 
to avoid it, 0.6in should be more reliable. On your 300dpi printer this 
particular QR code may be printed e.g. at ~(0.8/1.5)in.


Fix size of QR code pixel (module), not size of whole QR code.


- Find number of pixels in QR code in QR specs (or just calculate them)


Calculate them how or find them where?  Pdflatex somehow does it and
the QR-codes are fine when printed on a laser printer and when shown
on a 4k display.


"Modules" in Florent's message is what I referred to as QR code "pixels" 
and their count depends on "version".



- Specify width and height so that the ration of 2 numbers above is a
whole number.

Image may become a bit larger or a bit smaller.


The QR-code must fit on the label, plus some text.  The labels are
50x35mm in size.


It limits amount of information you may put into QR codes. You can still 
choose to use e.g. 4,5,6, etc. printer dots per QR code module.



When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
Perhaps the pst-barcode package uses vector graphics?


Nice, however you have to adjust size to avoid blurring.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Florent Rougon]

Hi,

I haven't read the whole thread (sorry) but thought this might help.

hw  wrote:

> When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
> Perhaps the pst-barcode package uses vector graphics?

That is quite likely: the pst- prefix means this is PSTricks, which is
an oldish way of doing vector graphics with LaTeX. I tend to avoid
PSTricks these days as it is generally awkward to use in PDF contexts,
although there are various workarounds that often allow to do so.

The ubiquitous, powerful and modern way to do vector graphics in LaTeX
is PGF/TiKZ[1], however this is not even necessary for QR codes, because
these are made of perfect monochrome rectangles, which TeX can draw
natively using its \hrule and \vrule primitives.

> 'pdfimages -list' doesn't show any images for a PDF with QR-codes
> created with pdflatex.

AFAIK, 'pdfimages' would extract “actual images” embedded in a PDF file
(e.g., PNG or JPG), however here pst-barcode presumably uses PostScript
or PDF primitives for drawing and filling polygons, which in your case
probably end up as PDF primitives. Hence, 'pdfimages' can't see these QR
codes (AFAIUI).

I've played with a different package for producing QR codes in LaTeX,
which uses the aforementioned \hrule and \vrule primitives: qrcode. Its
manual is here (follow the “Package documentation” link):

  https://ctan.org/pkg/qrcode

Here is a simple example you can compile with pdflatex:

\documentclass{article}
\usepackage{qrcode}

\pagestyle{empty}

\begin{document}

\noindent
% \qrset affects \qrcode commands in the current group. You can use it
% to factor out options used for several QR codes.
\qrset{nolinks, padding}% add padding to make sure the codes are 
“legal”/readable
\qrcode[version=1]{Hey Debian-user!}% Can't do version=1 with level=M or more
\qrcode[level=L, version=1]{Hey Debian-user!}% Less redundancy but is doable

\end{document}

Note the terminal output:














There are several quality levels allowing error correction (see the
manual): Low, Medium, Quality, and High. They correspond to 'level'
values L, M, Q, H. Default is M but if the chosen 'version' (which maps
to a specific number of modules) allows for a better level, qrcode
automatically upgrades to the best level possible for the chosen
'version' (which the above log demonstrates for the first QR code).

My example tries to print two QR codes with version=1, which means
21×21 modules (see below). Using the default level (M), this is not
possible for the specified text, therefore the first QR code is drawn as
a version=2 one (i.e., it has 25×25 modules). For the second QR code, I
explicitly ask for level=L which has the worst redundancy for error
correction; this allows "Hey Debian-user!" to be QR-encoded with
version=1, i.e. as a square of 21×21 modules.

The length of what you are encoding obviously dictates which quality
parameters you can afford, so you need to play with actual text for your
application. You can control the size of the QR code with e.g.
\qrcode[height=1cm]{...}. Since the modules are stuck to each other,
once you've determined an appropriate 'version' parameter, you can
easily choose a height that causes the modules to have the exact size
you want in the resulting PDF file (printer driver issues are out of my
league).

Regarding the 'version' parameter:

  version=1  → 21×21 modules
  version=2  → 25×25 modules
  version=3  → 29×29 modules
  ...
  version=40 → 177×177 modules

(each version step adds 4 to the number of modules in each direction)

So, you may want to play with text of yours and these parameters.
Examine the terminal output or log file to make sure the qrcode package
didn't have to increase the 'version' in order to encode the text you
specified. Note that in my example, the second QR code scanned with a
smartphone from a computer screen display seems to be significantly
harder to recognize than the first one (IOW, using level=L is probably a
bad idea even though it allows one to reduce the number of modules. But
with low printer resolution constraints, who knows?).

Hope this helps!

Regards

[1] https://ctan.org/pkg/pgf

-- 
Florent

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 11/3/24 07:34, hw wrote:

Do you think that thermal transfer printers with 203dpi would be
better suited to print QR codes than the 300dpi multi-mode printers?

I'm not fond of thermal transfer at all.  Usually what is being
printed that way fades rather quickly over time and is more slightly
gray rather than black and so thin that it's hard to read even when
freshly printed.  Perhaps better labels are available, but the labels
must not get too expensive ...



Thermal transfer and thermal direct printers have the same resolution.

Thermal transfer printers are used for archival labels as they fade very 
little over time.


Direct thermal printers are intended for mailing applications where it 
doesn't matter if they fade after a few months.


Given that, I think a lot of commercial shippers use thermal transfer 
for mailing labels. Very few shippers use laser printed adhesive address 
label, nor non-adhesive in pockets or pouches.


To print a QR code or other 2D code on any thermal printer, the printer 
manufacturer will supply an application that generate the codes and 
prints them independently of the host printing system. These codes will 
scan perfectly.


It is possible to use document generation tools like latex and printing 
systems like CUPS to print a label, but pixel registration will be poor. 
The only practical option for this route is to print the code BIG

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Sun, 2024-03-10 at 09:50 +0700, Max Nikulin wrote:
> On 10/03/2024 04:41, hw wrote:
> > \psbarcode{textblah foo}{height=0.6 width=0.6 eclevel=L}{qrcode}
> > 
> > That works for 600dpi laser printers.  When you print the QR-code with
> > a 300dpi label printer you can't reliably scan it, not even when you
> > make the QR-code 1x1" in size.
> > 
> > Perhaps that's not a reasonable size?
> 
> Perhaps height and width are chosen improperly. An image some percents 
> smaller may be sharper.

What size do you consider reasonable?

> - Find the dpi value in the specs of your printer

300dpi

> - Find number of pixels in QR code in QR specs (or just calculate them)

Calculate them how or find them where?  Pdflatex somehow does it and
the QR-codes are fine when printed on a laser printer and when shown
on a 4k display.

> - Specify width and height so that the ration of 2 numbers above is a 
> whole number.
> 
> Image may become a bit larger or a bit smaller.

The QR-code must fit on the label, plus some text.  The labels are
50x35mm in size.

That limits the QR-code to about 1x1", give or take a few mm.  1" is
already half the width of the label which doesn't leave much room for
text, and you have to give it some slack because you want to end up
printing somewhere on the label and not on the gaps between the
labels.

When I zoom in on QR-codes in a PDF viewer, they don't get blurry.
Perhaps the pst-barcode package uses vector graphics?

'pdfimages -list' doesn't show any images for a PDF with QR-codes
created with pdflatex.



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Sun, 2024-03-10 at 07:56 +0800, jeremy ardley wrote:
> On 10/3/24 05:41, hw wrote:
> > The QR-codes are sharp and easily scanable when printed in 600dpi.
> > With the label printer you can't really tell if they're sharp or not.
> 
> As  mentioned in my previous post, thermal label printers are 203dpi, 
> *not the 300 that the OP quoted.*

The printers I've been printing on are 300dpi and can do both thermal
and ribbon/ink.  I haven't tried thermal.

> [...]
> The data_matrix code (like a QRcode) for the same 41 digits is a 26x26 matrix 
> which at 203dpi can have pixels of 8x8 dots in a field of 26x26mm. These are 
> super easy for a thermal printer

Do you think that thermal transfer printers with 203dpi would be
better suited to print QR codes than the 300dpi multi-mode printers?

I'm not fond of thermal transfer at all.  Usually what is being
printed that way fades rather quickly over time and is more slightly
gray rather than black and so thin that it's hard to read even when
freshly printed.  Perhaps better labels are available, but the labels
must not get too expensive ...



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Sun, 2024-03-10 at 10:21 +0700, Max Nikulin wrote:
> On 10/03/2024 03:48, jeremy ardley wrote:
> > 
> > Standard thermal label printers are 203DPI (8 dots per mm).
> 
> Thanks, this number suits better to my expectation. I just trusted hw 
> earlier.

I should clarify:

The printer the OP pointed to seems to be rated at 203DPI and I
somehow thought it had 300dpi.  (203 seems very odd.)

The printers I have been trying to print QR-codes on are actually
300dpi printers.  They can do both thermal transfer or use a ribbon
that transfers ink to the labels kinda like typewriters did.  I
haven't used the thermal transfer mode and only the ribbon/ink mode.

> > I have asked the postal service to generate labels at 203dpi which will 
> > print just fine at 600 dpi and so work with laser and thermal printers, 
> > but they will not cooperate.

Why would they create labels that can not be scanned when printed?

Maybe ask them to print the labels for you?  If they can't scan them
then that's their problem.



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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 10/3/24 15:39, Max Nikulin wrote:
From your earlier message I count approximately 1000px for 5in (125 
mm) barcode. If it is 1:1 to ~200dpi then it is incompatible with 
300dpi printers, so it may be a reason why your proposal to the post 
office was rejected. If it is 500 black or white lines and each one 
occupies 2 printer dots then 300dpi image of the same size has 3 dots 
per line. (Sorry, I am unsure concerning "module" term.) You should be 
able to rasterize PDF files to 600dpi (2x factor) and downsample them 
by 1/3 keeping lines sharp.


In barcodes such as Code-128 a module is 12 'slots' which at minimum is 
one pixel per slot or 12 pixels. Code-128 has over 100 character 
encodings in a module.


So code 128 on a 203dpi printer 12 * characters / 8 mm e.g. for 40 
characters it's 12*40/8 = 60mm. 2 pixels per module make it 120mm. 3 
pixels per module make it 180mm so too big for mailing labels.


As for my post office, their barcodes do not match 300dpi or 600dpi. 
They are scaled at about 75-80% of what they should be. I'm really 
surprised they work. I can only guess most people use 1200dpi.


Thermal labels are the way to go as they stick really well and resist 
water. They are also *cheap*. around 1-2 cents in bulk for 100x150 . 
Plastic envelope and laser printed label will cost 10-20c. A self 
adhesive laser label is getting on to 50c.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 10/03/2024 10:51, jeremy ardley wrote:


I have far less problems with the QR code (in my case data_matrix code) 
than with the barcode. The pixel elements of the QR code are much larger 
than the lines in a barcode so there is much less chance for pixel 
ambiguity.


From your earlier message I count approximately 1000px for 5in (125 mm) 
barcode. If it is 1:1 to ~200dpi then it is incompatible with 300dpi 
printers, so it may be a reason why your proposal to the post office was 
rejected. If it is 500 black or white lines and each one occupies 2 
printer dots then 300dpi image of the same size has 3 dots per line. 
(Sorry, I am unsure concerning "module" term.) You should be able to 
rasterize PDF files to 600dpi (2x factor) and downsample them by 1/3 
keeping lines sharp.


Certainly this simple trick would fail if QR in the same file requires 
3/4 scaling.



from pdf2image import convert_from_path


The pdfimage(1) tool may extract images in their original format, 
perhaps there is a similar python module.



     detected_codes = pyzbar.decode(img)


Each barcode and QR code may be resampled individually without 
recognizing it. If position of each image on the page is known,
resampled images may be put back to correct places in the document 
rasterized to your printer resolution.


P.S. Post office guys may believe that labels created using laser 
printers are more resistant to wearing during processing and delivery, 
so 300dpi resolution may be intentional to discourage usage of thermal 
printers.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 10/3/24 11:21, Max Nikulin wrote:


Is the QR image a raster one? I am unsure concerning its printer dots 
per QR pixel ratio. Let's take e.g. 4 as a value inconvenient for 
direct scaling from 300dpi to 203dpi. I expect that upscaling it by 3 
and downscaling the result by 4 with disabled smoothing (e.g. using 
splines) should generate an image that is 1.5% larger than the one 
suitable for 203dpi. So setting 98.5% scaling for printer should allow 
to achieve sharp QR image without re-encoding QR.



In my case I have never seen a bigger dogs breakfast of a pdf! It has 
many elements in different formats including bitmaps, scalable vector 
graphics, and text elements. That and some images are colour and some 
black and white. I just preprocess it


I have far less problems with the QR code (in my case data_matrix code) 
than with the barcode. The pixel elements of the QR code are much larger 
than the lines in a barcode so there is much less chance for pixel 
ambiguity.


I think i you make it 'big enough' it will scan fine. So a factor of 2 
magnification should work with a QR code.


I spent many (un)happy hours with gimp and imagemagick to try and get 
the best solution for barcodes. Sadly there is none other than print the 
barcode as big as possible in your page real-estate.


I spent an hour today with my friend GPT4 and python and I can now pluck 
out any and all codes from my mailing labels and I next plan to generate 
new labels at 203dpi using freshly encoded barcodes and data_matrix codes.


Here is some experimental code

from PIL import Image
import pyzbar.pyzbar as pyzbar
import qrcode  # For generating QR codes
from barcode import EAN13, generate  # Using EAN13 as an example; this 
might vary

from barcode.writer import ImageWriter
import os

from pdf2image import convert_from_path

def pdf_to_image(pdf_path, dpi=600):
    images = convert_from_path(pdf_path, dpi=dpi)
    for img in images:
    yield img

def detect_and_extract_codes(images):
    for img in images:
    detected_codes = pyzbar.decode(img)
    for code in detected_codes:
    print(code)
    if code.type == 'QRCODE':
    # Process QR code
    process_qr_code(code)
    else:
    # Process other types of barcodes
    process_barcode(code)

def process_qr_code(code):
    qr = qrcode.QRCode(
    version=1,
    error_correction=qrcode.constants.ERROR_CORRECT_L,
    box_size=10,
    border=4,
    )
    qr.add_data(code.data.decode())
    qr.make(fit=True)
    img = qr.make_image(fill_color="black", back_color="white")
    img.show()  # Or save the image

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 10/03/2024 03:48, jeremy ardley wrote:


Standard thermal label printers are 203DPI (8 dots per mm).


Thanks, this number suits better to my expectation. I just trusted hw 
earlier.


I have asked the postal service to generate labels at 203dpi which will 
print just fine at 600 dpi and so work with laser and thermal printers, 
but they will not cooperate.


Is the QR image a raster one? I am unsure concerning its printer dots 
per QR pixel ratio. Let's take e.g. 4 as a value inconvenient for direct 
scaling from 300dpi to 203dpi. I expect that upscaling it by 3 and 
downscaling the result by 4 with disabled smoothing (e.g. using splines) 
should generate an image that is 1.5% larger than the one suitable for 
203dpi. So setting 98.5% scaling for printer should allow to achieve 
sharp QR image without re-encoding QR.


You may try to find rational approximation for (4*208)/300 better than 
4/3 (or for actual QR pixel size).

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 10/03/2024 04:41, hw wrote:

\psbarcode{textblah foo}{height=0.6 width=0.6 eclevel=L}{qrcode}

That works for 600dpi laser printers.  When you print the QR-code with
a 300dpi label printer you can't reliably scan it, not even when you
make the QR-code 1x1" in size.

Perhaps that's not a reasonable size?


Perhaps height and width are chosen improperly. An image some percents 
smaller may be sharper.


- Find the dpi value in the specs of your printer
- Find number of pixels in QR code in QR specs (or just calculate them)
- Specify width and height so that the ration of 2 numbers above is a 
whole number.


Image may become a bit larger or a bit smaller.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 10/3/24 05:41, hw wrote:

The QR-codes are sharp and easily scanable when printed in 600dpi.
With the label printer you can't really tell if they're sharp or not.


As  mentioned in my previous post, thermal label printers are 203dpi, 
*not the 300 that the OP quoted.*


you can read the OP specs here which say 203. 
.


Thermal label printers have no problems printing even long bar codes, QR codes, 
and data_matrix codes if the generator uses the correct dpi and the print 
process maintains the pixel mapping.

In my case my barcodes are 41 digits long (extreme GS1 !) and at 2 pixels per 
module (12 modules per digit) it is 123mm long which fits into a 150x100 
thermal label

The data_matrix code (like a QRcode) for the same 41 digits is a 26x26 matrix 
which at 203dpi can have pixels of 8x8 dots in a field of 26x26mm. These are 
super easy for a thermal printer

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[hw]

On Sat, 2024-03-09 at 23:20 +0700, Max Nikulin wrote:
> On 09/03/2024 19:08, hw wrote:
> > On Fri, 2024-03-08 at 23:21 +0700, Max Nikulin wrote:
> > > On 08/03/2024 12:35, hw wrote:
> > > > On Thu, 2024-03-07 at 23:15 -0500, Jeffrey Walton wrote:
> > > > > 
> > > > > I have a USB thermal printer for the shipping labels,
> > > > > .
> > > > 
> > > > This printer has only 300dpi.  If you print QR-codes on it make sure
> > > > you can scan them: they have to be large enough or get you an
> > > > unscanable smear.
> > > 
> > > I believed that 300dpi is high enough resolution for QR-codes of
> > > reasonable size if source image has proper quality. On the other hand,
> > > if possible, it is better to scale QR-codes to match some whole factor
> > > of printer pixel size.
> > 
> > What do you consider a 'reasonable size'?
> 
> Looking at a QR code likely having ~75 pixels per inch I find it 
> unreasonably small for delivery labels.

Shipping labels tend to be pretty large.

> I am in doubts if its redundancy is high enough to reliably
> recognize it if it would be scratched during delivery. Another

Increased redundancy can make the QR-code harder or impossible to
scan because it creates more smear instead of more redundancy.

Once you've seen what that looks like, it is evident that smearing
more ink into the same area for more redundancy makes things only
worse.  You'd have to print the QR-code larger.

> limitation may be stability of optics in scanners in respect to
> labels. This one is printed using a laser printer with resolution at
> least 600 dpi. Each QR code pixel has still 4x4 printer dots in the
> case of 300dpi, so when image is properly aligned, printer quality
> is not an issue.

Yes, the QR-codes printed on a 600dpi laser printer are fine.

> > There is no source image other than whatever LaTeX creates.  I can
> > specify the size of the QR-code.  Other than that, how do you apply
> > scaling?
> 
> I am unsure what particular QR code generator do you use and what is the 

I'm using the pst-barcode package and pdflatex to create a PDF file
which is then sent through cups to the printer.  So LaTeX, the
bst-barcode package, some PDF stuff, the printer driver, the printer
and it's settings for darkness and printing speed, the material the
labels are made of and the ribbon with the ink on it which gets
transferred to the label all influence the result.

Also, labels are continuously being fed through the printer while
printing without stopping.  That makes some smear inevitable.

> format of QR codes.

It basically goes like this:

\psbarcode{textblah foo}{height=0.6 width=0.6 eclevel=L}{qrcode}

That works for 600dpi laser printers.  When you print the QR-code with
a 300dpi label printer you can't reliably scan it, not even when you
make the QR-code 1x1" in size.

Perhaps that's not a reasonable size?

> Is it raster or vector image? Specify size that makes QR code pixels
> having whole number of printer pixels.

I only know that the QR-code must fit on the label.

> "Fit to page" or "fit to printable area" in printer options may make an 
> image blurry.

No such options are specified.

> In the case of low input image resolution, upscaling method suitable
> for photos may make QR code blurry. However consistent configuration
> should make QR codes sharp.

IIRC there is an option to create a PDF having a particular
resolution, like 300DPI, but that didn't seem to have any effect.  I
don't remember what that option was :/

The QR-codes are sharp and easily scanable when printed in 600dpi.
With the label printer you can't really tell if they're sharp or not.




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Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[jeremy ardley]

On 10/3/24 00:20, Max Nikulin wrote:


Looking at a QR code likely having ~75 pixels per inch I find it 
unreasonably small for delivery labels. I am in doubts if its 
redundancy is high enough to reliably recognize it if it would be 
scratched during delivery. Another limitation may be stability of 
optics in scanners in respect to labels. This one is printed using a 
laser printer with resolution at least 600 dpi. Each QR code pixel has 
still 4x4 printer dots in the case of 300dpi, so when image is 
properly aligned, printer quality is not an issue. 


Standard thermal label printers are 203DPI (8 dots per mm).

The problem with printing QR codes and bar codes is not the resolution 
of the printer but getting the the software drivers to produce a bitmap 
that is the same resolution as the printer resolution and aligned at the 
pixel level when it goes to the printer


I have written a CUPS driver for a thermal printer and routinely print 
labels with barcodes and QR style codes. I have immense problems with 
PDF labels generated by my local postal service which are generated for 
a 300 DPI printer. The barcodes especially end up with too thick or too 
thin bars where the pixel mapping doesn't align. These will not scan.


I have asked the postal service to generate labels at 203dpi which will 
print just fine at 600 dpi and so work with laser and thermal printers, 
but they will not cooperate.


I am in the process of developing software to take the issued labels, 
extract the barcode and QR fields, decode them, and then generate new 
bitmaps at 203 dpi to replace  the misaligned bitmaps. This is not 
straight forward as the postal service does not fully comply with the 
coding rules.


In the meantime I have to extract the QR and bar code fields, enlarge 
them, and print on separate labels.


As far as printer drivers work, CUPS typically generates a bitmap from a 
source document such as PDF or postscript, and passes that to a raster 
printer. This in itself can be a problem as any stage of the process of 
generation of pdf, 'printing', and rasterisation can misalign and 
distort pixels. To be absolutely sure of clean output you need a custom 
program directly driving the printer.

Re: printing QR-codes on labels with 300dpi label printers with LaTeX

[Max Nikulin]

On 09/03/2024 19:08, hw wrote:

On Fri, 2024-03-08 at 23:21 +0700, Max Nikulin wrote:

On 08/03/2024 12:35, hw wrote:

On Thu, 2024-03-07 at 23:15 -0500, Jeffrey Walton wrote:


I have a USB thermal printer for the shipping labels,
.


This printer has only 300dpi.  If you print QR-codes on it make sure
you can scan them: they have to be large enough or get you an
unscanable smear.


I believed that 300dpi is high enough resolution for QR-codes of
reasonable size if source image has proper quality. On the other hand,
if possible, it is better to scale QR-codes to match some whole factor
of printer pixel size.


What do you consider a 'reasonable size'?


Looking at a QR code likely having ~75 pixels per inch I find it 
unreasonably small for delivery labels. I am in doubts if its redundancy 
is high enough to reliably recognize it if it would be scratched during 
delivery. Another limitation may be stability of optics in scanners in 
respect to labels. This one is printed using a laser printer with 
resolution at least 600 dpi. Each QR code pixel has still 4x4 printer 
dots in the case of 300dpi, so when image is properly aligned, printer 
quality is not an issue.



There is no source image other than whatever LaTeX creates.  I can
specify the size of the QR-code.  Other than that, how do you apply
scaling?


I am unsure what particular QR code generator do you use and what is the 
format of QR codes. Is it raster or vector image? Specify size that 
makes QR code pixels having whole number of printer pixels.


"Fit to page" or "fit to printable area" in printer options may make an 
image blurry. In the case of low input image resolution, upscaling 
method suitable for photos may make QR code blurry. However consistent 
configuration should make QR codes sharp.

printing QR-codes on labels with 300dpi label printers with LaTeX (was: libbusiness-us-usps-webtools-perl and USPS Ground Advantage shipping)

[hw]

On Fri, 2024-03-08 at 23:21 +0700, Max Nikulin wrote:
> On 08/03/2024 12:35, hw wrote:
> > On Thu, 2024-03-07 at 23:15 -0500, Jeffrey Walton wrote:
> > > 
> > > I have a USB thermal printer for the shipping labels,
> > > .
> > 
> > This printer has only 300dpi.  If you print QR-codes on it make sure
> > you can scan them: they have to be large enough or get you an
> > unscanable smear.
> 
> I believed that 300dpi is high enough resolution for QR-codes of 
> reasonable size if source image has proper quality. On the other hand, 
> if possible, it is better to scale QR-codes to match some whole factor 
> of printer pixel size.

What do you consider a 'reasonable size'?  The maximum possible size
of the QR-code is limited by the size of the label.  (Shipping labels
are probably big enough ...)

There is no source image other than whatever LaTeX creates.  I can
specify the size of the QR-code.  Other than that, how do you apply
scaling?




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