The role of QRCodeRatio1 in detecting slightly rotated large QR Codes
When the software scans for a Qr Code it first looks for finder target patterns. When one is located it scans further along the same scan line to see if it can locate another finder pattern. If it can then it estimates the locations of the third pattern and continues to try and read the Qr Code.
If it cannot find another finder pattern on the same scan line then it stores the location of the finder pattern for later. When the initial scan of the image is complete the software considers all possible triples of finder patterns to see if they may be part of the same Qr Code.
One of the tests in this process is the ratio of the width/height of the finder patterns to the horizontal/vertical distance between the center points of the target patterns. This is known as QRCodeRatio1 and has the value 8 by default.
The maximum possible value for this ratio in an image is approximately 24 (for a 177×177 module QR Code) and setting QRCodeRatio1 to 24 will have a performance impact because it will increase the number of triples considered when processing the finder targets, however it is debatable whether a QR Code of this complexity could be scanned at a slight rotation anyway unless at a very high resolution.
In tests there appears to be almost no change in performance between the default of 8 and the value of 10. There is a small change between 10 and 16 and a change of similar size between 16 and 24.
