QR Code Readability

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1) Size / distance – it’s not just a matter of size. Combining size / distance is what determines if a QR is readable or not.

2) Number of characters. The more information a QR contains the more “dense” it will be and that will make reading it more difficult.You could say that the more information contains the larger QR must be.

3) Level of error correction. The redundancy of information contained in a QR algorithm is given by (Red -Solomon ) pemitirá “play” with designs and customizations but that will be detrimental to readability.

4) Contrast with the base. If we use custom codes, we must control the contrast with the base (specially if you use yellow or light colors).

5 ) Phone lenses. This problem affects very smartphone cameras but if they are old they usually don’t have a good macros (ability to focus up close ) and this can also affect readibility of a QR for being too small ( < 2cm) .

 6) App used . There are hundreds if not thousands of applications reading QR- Codes in the various app stores and some are better than others. They all do essentially the same: identify, capture and read 2D codes but efficiency may vary.

7) Light. Even if the contrast is correct in “lab conditions”  if the QR is read in low light or in a backlighted surface (Eg. screen) it may become unreadable .

8) Angle . There is a tolerance of skewed catch the QR form 20-30 ° vertically or horizontally

9) Surface curvature. If you print a QR on a curved surface (Eg. Mug) if the size is not excessive it can be read .


The number of variables make trial and error the most reliable method to validate a QR face .

The best way to determine the size is “try , try and try .” It is very easy to print 3-4 different sizes and see how far QR can be shrunk.

Our advice is to borrow the worst smartphone and do the tests with this and average lighting conditions . If it works, it will always work.

Size and Distance

The QR code needs to be of a sufficient size to be scanned reliably; generally, the minimum size of the printed code should be one inch. In determining the size of the code you will also want to take into account the expected distance the user will be from the code when it is scanned. A good rule of thumb is to assume a 1:10 size-to-distance ratio, under ideal conditions. So if the code size is one inch, the user can be up to 10 inches away when the code is scanned. If you anticipate a scenario where users will be standing at a further distance then you will need to increase the size of the code accordingly (e.g. a product display where you anticipate users to be three feet away would call for a code of about 3.5 inches). If you anticipate more challenging conditions such as low-light, or low contrast, then a more conservative 1:8 size-to-distance ratio may be more suitable.

Color and Contrast

QR Codes are most commonly displayed as a black code on a white background, and with good reason, as this color combination provides the greatest contrast. Contrast is an important factor in scan reliability, so a black code on a white background is the safest display option in terms of color. However, it is also possible to display QR codes in a variety of colors, provided there is sufficient contrast between the foreground (code) and the background. Generally, the darker the color of the code, and the lighter the background, the more reliably the code will scan.

It is also possible to display a QR code in a reversed color pattern (light code on dark background), but this is not advisable, as many QR code readers cannot read the code if it is reversed out on a dark background.

Leave a Little Breathing Room

It's generally a good idea to have a margin of empty whitespace around the perimeter of the code (AKA the “quiet zone”), as objects positioned near the edge of the code can interfere with scan reliability. The quiet zone should be equal to at least four of the modules (little squares) within the code.

Positioning and Interference

It's important to think about the literal placement of the code, to ensure that there are no obstructions that could interfere with getting a clean scan. For example, if a code is placed too close to the edge of the fold in a magazine it might be difficult to get the code to scan correctly. If a code is placed on a billboard you would want to make sure there were no wires, branches or other items that would cross the visual path of the code and interfere with scanning.

Media and Material

QR codes can be placed on just about anything that can accept printing, including paper, plastics and fabric, as well as electronic/screen-display. Generally speaking, QR codes should be placed on a flat surface that is not reflective, in order to avoid glare (think matte rather than gloss). Materials that are porous or bumpy are not ideal for QR code presentation.

Environmental Factors

Consider the environment in which the code will be placed – will it be pretty consistent, or might it change in ways that could affect the scan reliability of the code? For example, can you assume that there will always be sufficient lighting, or will lighting conditions change; is the code on a material that could cause glare in sunlight? Also consider connectivity - since most codes send users to some web-based destination it's also important to ensure that there is a reliable data connection (3G, 4G, WiFi) within the immediate area where the code will be placed.

The Math

Explanation: http://www.qrcode.com/en/howto/generate.html

Simple Formula:

Minimum Size = QR Code Scanning Distance / 10

Improved formula :

QR Code Minimum Size = (Scanning Distance / Distance Factor) * Data Density Factor

Links to STUFF QR- with mathematical formula to calculate the size of a QR .



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