5 ms·

QR error correction helps and hinders scanning (2021)

78 points by lucb1e 3y ago

lucb1e 3y ago
Combined one of the section headings in the text, which basically gives away the conclusion, with the caveat that it's about undamaged QR codes. As you can expect more damage (such as when tattooing one, or paper that goes around), higher error correction does make sense; same when overlaying graphics/logos. I found this surprising. I'll be displaying QR codes on a screen, so for me L easily makes the most sense in order to be able to make it larger with fewer squares inside of it.
deleted 3y ago
[deleted]
cratermoon 3y ago
The airline industry uses other kinds of 2D codes, like Aztec Codes[1] or Imagen PDF417 on your boarding passes, including the digital ones you have on your phone. For example: https://fwhibbit.es/wp-content/uploads/2017/07/3-1.png https://fwhibbit.es/wp-content/uploads/2017/07/3-1.png 1 https://en.wikipedia.org/wiki/Aztec_Code https://en.wikipedia.org/wiki/Aztec_Code
- sbierwagen 3y ago
  The barcode on the back of North American driver's licenses is also a PDF417. Amusingly enough, it encodes all the text on the front of the license. Name, DOB, weight, height, etc. Retailers that scan your license for alcohol age limit checks get a lot of data they don't technically need.
  - labster 3y ago
    Finally, a justification for lying about your weight on your license.
  - chocolatkey 3y ago
    I remember that the WeWork location I went to used to scan (and likely siphon/store) all that data as part of the front desk check-in. And they really didn't need it either, but were very insistent on doing so before letting someone know I (a guest) was in the lobby
  - ProllyInfamous 3y ago
    ProTip™: US Passports are ACCEPTABLE FORMS OF ID (in all US Jurisdictions), and are not able to be scanned for these types of purchases.
    - vlovich123 3y ago
      For what it’s worth MDL, the digital driver’s license, has this baked in unless the standard changed since I paid attention - your identity authority signs a record saying >18 and >21 (+ photo) and that’s what’s transmitted.
      - ggm 3y ago
        Qld government spent $18m making its own digital license app ignoring that Apple and Google both implement the iso specification for digital ID protection. I've had two interactions online with sw people convinced "they did it better" and I am buggered if I can tell how.
        vlovich123 3y ago
        Typically what happens is that consultants implement the IT systems for these departments. Unfortunately it wouldn’t surprise me if the government got snowed into thinking they needed this app / there are kickbacks involved behind the purchasing decision. Still, it is possible the app has a legit reason like the OS wallet implementation is missing support for their region or OS wallet support is incomplete in some way and this bridges that gap. 18m does seems a tad steep though considering that RDW payed UDL to build a sample reference app for free and one would expect that to be the basis for any 3p implementation delivered. Like that would be 36 very highly paid engineers which is a lot for 2 apps. It’s possible the 18m was also for the backend changes to enable the app which would maybe be more legit and be required changes for the builtin integration. Are you sure it was 18m just for the app?
        deleted 3y ago
        [deleted]
        3y ago
MauranKilom 3y ago
The part that makes higher error correction even more pointless is that errors can only be tolerated well in certain parts of the QR code. If the position markers are damaged, a scanner likely won't even recognize that there is a QR code visible, which obviates any error correction. The article mentions this in the very last sentence/caveat. It feels a bit like the error correction exists mainly so you can embed fancy logos in your QR code... Avoiding damage to some parts but not others seems unaligned with real world scenarios...
- charcircuit 3y ago
  Since the position markers are constant they should be the easiest to recover if damaged. Considering how advanced computer vision is, a QR code can be identified without using them.
  - londons_explore 3y ago
    Agreed - QR recognition/alignment algorithms can clearly be improved further, and then when they are, higher error correction codes ought to be more reliable as designed.
  - cbzoiav 3y ago
    It's not a case of can they be. It's a case of can they cheaply be. The camera app on your smartphone likely searches for them by default. That means feeding at least 1-2 frames a second through it. Basic pattern matching for the position markers is a rounding error overhead vs processing a video feed. Fancy computer vision is not - on lower end devices you may not have enough resources to do both and on higher end devices it'll still impact power usage.
    - cwillu 3y ago
      Low tech stupid solution: carry a sharpie.
      - foota 3y ago
barbegal 3y ago
It's the same for wireless protocols too. Transmitting with less bits per symbol makes the whole packet longer and potentially more prone to interference. Transmitting at a higher symbol rate can often reduce the amount of packets lost which is counterintuitive.
- deleted 3y ago
  [deleted]
lettergram 3y ago
Why are we even using black and white tags? https://austingwalters.com/chromatags/ https://austingwalters.com/chromatags/
- charcircuit 3y ago
  Because printing binary black and white is cheaper to print and cheaper to read.
  - 1letterunixname 3y ago
    That was the case in 2005, but now nearly every camera in public and industrial use supports color except save some in particular logistics uses that would need upgrading. The only reason it remains is legacy and convention. Yes, it requires different printers, but that's not an insurmountable supply chain change, especially if it's reduced to a few distinct colors that don't need to be mixed. This is a missed opportunity to encode more data into a given area and/or to make it more readable.
    - p3n1s 3y ago
      > nearly every camera in public and industrial use supports color This is essentially false. Plenty of industrial cameras are black and white because of their speed and light collecting advantages. This matters for high speed identification. Going to color would not be an upgrade. "missed opportunity" Limited information density just isn't nearly as big an issue as you seem to believe. Colors work great until they don't, for non emissive sources they depend on ambient lighting. A black and white code can be read with under virtually any color lighting (it doesn't even have to be in the visible spectrum). And if you've seen anyone futzing getting a read of an eticket off an emissive device such as a screen, that is just much worse once color is brought in. Most auto ID applications have limited keys and identifiers encoded in the symbol. Just as color cameras are ubiquitous, the same goes for network connectivity, you don't need to store massive amounts of data in the symbol. If color symbols were really that much of a win they would have been adopted in industry. Attempts by groups that don't understand the subject have been made over the years, this is not new: https://en.wikipedia.org/wiki/High_Capacity_Color_Barcode https://en.wikipedia.org/wiki/High_Capacity_Color_Barcode "Yes, it requires different printers" This is quite an understatement. There's no cheap upgrade path from monochrome thermal printing technology (or laser engraving), that's why they have never been replaced all these years. Color imagers were readily available long before 2005. Color printing has not changed much at all in the past 20 years. If color symbols made sense they would have been adopted a long time ago. They are almost always the wrong approach, too many problems for too little payoff, that's why they are uncommon.
kazinator 3y ago
The weasel word in the title is undamaged. But the story is actually about QR codes being damaged. The original image isn't damaged, but its impression is damaged in transit while being scanned. QR codes crammed with more information (such as more error correction) have smaller pixels for the same view angle, and those are more easily damaged during the scan. An undamaged QR code with large pixels (low information) might scan perfectly without any error correction at all, but as the information density increases, so does the potential for error (error not caused by damage in the QR code being scanned). If we make a QR code so dense that the scanner cannot make out any of the pixels, it becomes completely unreliable, even if 80% of it is error correction bits. Basically, error correction defends against processes that cause random erasure or flipping of bits. Error correction is not meant to defend against fundamental channel bandwidth problems.
- vlovich123 3y ago
  Said another way if I understand correctly, erasure codes help as long as message + erasure fits into channel bandwidth. If it doesn’t, then erasure codes hurt. Is that right?
  - deleted 3y ago
    [deleted]
- BobbyTables2 3y ago
  [dead]
- deleted 3y ago
  [deleted]

78 points by lucb1e 3y ago

Combined one of the section headings in the text, which basically gives away the conclusion, with the caveat that it's about undamaged QR codes. As you can expect more damage (such as when tattooing one, or paper that goes around), higher error correction does make sense; same when overlaying graphics/logos. I found this surprising. I'll be displaying QR codes on a screen, so for me L easily makes the most sense in order to be able to make it larger with fewer squares inside of it.

deleted 3y ago

[deleted]

cratermoon 3y ago

The airline industry uses other kinds of 2D codes, like Aztec Codes[1] or Imagen PDF417 on your boarding passes, including the digital ones you have on your phone. For example: https://fwhibbit.es/wp-content/uploads/2017/07/3-1.png https://fwhibbit.es/wp-content/uploads/2017/07/3-1.png 1 https://en.wikipedia.org/wiki/Aztec_Code https://en.wikipedia.org/wiki/Aztec_Code

sbierwagen 3y ago
The barcode on the back of North American driver's licenses is also a PDF417. Amusingly enough, it encodes all the text on the front of the license. Name, DOB, weight, height, etc. Retailers that scan your license for alcohol age limit checks get a lot of data they don't technically need.
- labster 3y ago
  Finally, a justification for lying about your weight on your license.
- chocolatkey 3y ago
  I remember that the WeWork location I went to used to scan (and likely siphon/store) all that data as part of the front desk check-in. And they really didn't need it either, but were very insistent on doing so before letting someone know I (a guest) was in the lobby
- ProllyInfamous 3y ago
  ProTip™: US Passports are ACCEPTABLE FORMS OF ID (in all US Jurisdictions), and are not able to be scanned for these types of purchases.
  - vlovich123 3y ago
    For what it’s worth MDL, the digital driver’s license, has this baked in unless the standard changed since I paid attention - your identity authority signs a record saying >18 and >21 (+ photo) and that’s what’s transmitted.
    - ggm 3y ago
      Qld government spent $18m making its own digital license app ignoring that Apple and Google both implement the iso specification for digital ID protection. I've had two interactions online with sw people convinced "they did it better" and I am buggered if I can tell how.
      - vlovich123 3y ago
        Typically what happens is that consultants implement the IT systems for these departments. Unfortunately it wouldn’t surprise me if the government got snowed into thinking they needed this app / there are kickbacks involved behind the purchasing decision. Still, it is possible the app has a legit reason like the OS wallet implementation is missing support for their region or OS wallet support is incomplete in some way and this bridges that gap. 18m does seems a tad steep though considering that RDW payed UDL to build a sample reference app for free and one would expect that to be the basis for any 3p implementation delivered. Like that would be 36 very highly paid engineers which is a lot for 2 apps. It’s possible the 18m was also for the backend changes to enable the app which would maybe be more legit and be required changes for the builtin integration. Are you sure it was 18m just for the app?
        deleted 3y ago
        [deleted]
        3y ago

MauranKilom 3y ago

The part that makes higher error correction even more pointless is that errors can only be tolerated well in certain parts of the QR code. If the position markers are damaged, a scanner likely won't even recognize that there is a QR code visible, which obviates any error correction. The article mentions this in the very last sentence/caveat. It feels a bit like the error correction exists mainly so you can embed fancy logos in your QR code... Avoiding damage to some parts but not others seems unaligned with real world scenarios...

charcircuit 3y ago
Since the position markers are constant they should be the easiest to recover if damaged. Considering how advanced computer vision is, a QR code can be identified without using them.
- londons_explore 3y ago
  Agreed - QR recognition/alignment algorithms can clearly be improved further, and then when they are, higher error correction codes ought to be more reliable as designed.
- cbzoiav 3y ago
  It's not a case of can they be. It's a case of can they cheaply be. The camera app on your smartphone likely searches for them by default. That means feeding at least 1-2 frames a second through it. Basic pattern matching for the position markers is a rounding error overhead vs processing a video feed. Fancy computer vision is not - on lower end devices you may not have enough resources to do both and on higher end devices it'll still impact power usage.
  - cwillu 3y ago
    Low tech stupid solution: carry a sharpie.
    - foota 3y ago

barbegal 3y ago

It's the same for wireless protocols too. Transmitting with less bits per symbol makes the whole packet longer and potentially more prone to interference. Transmitting at a higher symbol rate can often reduce the amount of packets lost which is counterintuitive.

deleted 3y ago
[deleted]

lettergram 3y ago

Why are we even using black and white tags? https://austingwalters.com/chromatags/ https://austingwalters.com/chromatags/

charcircuit 3y ago
Because printing binary black and white is cheaper to print and cheaper to read.
- 1letterunixname 3y ago
  That was the case in 2005, but now nearly every camera in public and industrial use supports color except save some in particular logistics uses that would need upgrading. The only reason it remains is legacy and convention. Yes, it requires different printers, but that's not an insurmountable supply chain change, especially if it's reduced to a few distinct colors that don't need to be mixed. This is a missed opportunity to encode more data into a given area and/or to make it more readable.
  - p3n1s 3y ago
    > nearly every camera in public and industrial use supports color This is essentially false. Plenty of industrial cameras are black and white because of their speed and light collecting advantages. This matters for high speed identification. Going to color would not be an upgrade. "missed opportunity" Limited information density just isn't nearly as big an issue as you seem to believe. Colors work great until they don't, for non emissive sources they depend on ambient lighting. A black and white code can be read with under virtually any color lighting (it doesn't even have to be in the visible spectrum). And if you've seen anyone futzing getting a read of an eticket off an emissive device such as a screen, that is just much worse once color is brought in. Most auto ID applications have limited keys and identifiers encoded in the symbol. Just as color cameras are ubiquitous, the same goes for network connectivity, you don't need to store massive amounts of data in the symbol. If color symbols were really that much of a win they would have been adopted in industry. Attempts by groups that don't understand the subject have been made over the years, this is not new: https://en.wikipedia.org/wiki/High_Capacity_Color_Barcode https://en.wikipedia.org/wiki/High_Capacity_Color_Barcode "Yes, it requires different printers" This is quite an understatement. There's no cheap upgrade path from monochrome thermal printing technology (or laser engraving), that's why they have never been replaced all these years. Color imagers were readily available long before 2005. Color printing has not changed much at all in the past 20 years. If color symbols made sense they would have been adopted a long time ago. They are almost always the wrong approach, too many problems for too little payoff, that's why they are uncommon.

kazinator 3y ago

The weasel word in the title is undamaged. But the story is actually about QR codes being damaged. The original image isn't damaged, but its impression is damaged in transit while being scanned. QR codes crammed with more information (such as more error correction) have smaller pixels for the same view angle, and those are more easily damaged during the scan. An undamaged QR code with large pixels (low information) might scan perfectly without any error correction at all, but as the information density increases, so does the potential for error (error not caused by damage in the QR code being scanned). If we make a QR code so dense that the scanner cannot make out any of the pixels, it becomes completely unreliable, even if 80% of it is error correction bits. Basically, error correction defends against processes that cause random erasure or flipping of bits. Error correction is not meant to defend against fundamental channel bandwidth problems.

vlovich123 3y ago
Said another way if I understand correctly, erasure codes help as long as message + erasure fits into channel bandwidth. If it doesn’t, then erasure codes hurt. Is that right?
- deleted 3y ago
  [deleted]
BobbyTables2 3y ago
[dead]
deleted 3y ago
[deleted]