Frame alignment detection - jareff-g/ALT-Scann8 GitHub Wiki

In February 2025, suggested by one of the Discord channel users, a new feature was introduced to detect, while scanning, frames not correctly aligned. The purpose of this feature is to be able to quickly determine the quality of a given scan session, allowing us to discard if the proportion of misaligned frames is too high. Two kids of 'bad' frames are counted:

• Misaligned frames: These are frames which are not vertically centered, meaning that part of the top or bottom of the frame is out of the captured image. It is possible to tune how strict this check is by using the 'Misalign tolerance' parameter in the settings window. It is relevant to note that frames in this case can be partially 'fixed' in AfterScan by using the 'Fake fill' feature.
• Empty frames: Frames in this case are not necessarily errors, just frames that cannot be properly recognized. Most of the time the frame is completely empty (black or transparent film), or the frame is badly overexposed, so that the sprocket holes can be hardly recognized. These frames are left as-is (maybe another feature to skip them could be introduced in ALT-Scann8?)

Besides this new feature in ALT-Scann8, and since the detection code was already written, a standalone python app has been created (FrameAlignmentChecker.py) to allow performing the same alignment check on an existing set of frames. The results are displayed in the app and also logged to a file (same as in ALT-Scann8). To facilitate the analysis, the frames listed can be displayed by clicking on them with the mouse.