TLDR: We have observed that the bar code reader results are different when source images are rotated 90 degrees, or when the rectangle defining the read region is changed.
We are reading i2of5 and DataMatrix bar codes on image files scanned from A4 sized paper at 200dpi. We observed that the reading was very slow on the full page, so we added a rectangular region where we search for each bar code. One of the bar codes is used to determine the orientation of the paper in the scan, so we look for it on all 4 corners.
First, we noticed that the read success rate changed when we added the rectangles, and second, we noticed that the read success rate was sensitive to changes in the rectangle size. We are unable to determine how to correctly size the rectangle for maximum success, only that changing the rectangle changes the results.
We also observed some variability on the read success if the bar codes were rotated 90 degrees. In particular, bar codes that are vertical with right orientation have a success rate about 75% of all the other orientations.
Is there any guidance you can give on sizing the read rectangle for maximum success, and is there some reason we should see lower read success with right oriented barcodes?