Scanning

Scanning

This page is about getting images into OMRFlow. Reading them is Processing.

Scanner settings

OMRFlow has no preferred scanner. What matters is the image:

	Recommendation
Resolution	150–300 dpi. Lower loses bubble definition; higher mostly costs time and disk
Colour	Greyscale is enough. Colour is accepted
Format	PNG, JPEG, TIFF and the other formats OpenCV reads
Page	The whole sheet, including all four registration markers. A cropped edge is the most common cause of a sheet failing to register
Orientation	Any. OMRFlow detects which way up a page is from the orientation mark
Skew	Tolerated and corrected. Feed the sheets straight anyway
Compression	Avoid heavy JPEG compression; the artefacts land on the bubble edges

Use the same resolution for the reference image in your template and for the real scans. It is not strictly required — coordinates are normalised — but it keeps the calibration you tuned meaningful.

Importing

On the Scan stage:

1. Load Template… — the template these sheets were printed from. The panel names it and warns if it has not been calibrated since it last changed.
2. Add Scan(s)… for individual files, or Add Folder… for a whole folder. A folder is read in natural order, so sheet2 comes before sheet10.
3. Clear Scan List empties the list without touching the files.

Duplicate and changed scans

OMRFlow hashes each imported image's contents. It can therefore tell you that:

• you have imported the same image twice, even under a different name;
• a source image that was processed earlier is now missing;
• a source image has changed since it was read.

Scans are referenced rather than copied into the project, so keep the source folder. If you move it, see Moving Projects.

Output filenames

With renaming enabled, a recognised sheet is copied to an output folder named by its roll number. An existing file is never overwritten — a collision gets a distinct name and is reported, because two sheets claiming the same roll number is exactly the kind of thing you need to be told about.

Exporting

Export CSV writes the batch's recognised values, including the symbols for blank, multiple and uncertain marks, so nothing is silently flattened.

Related

• Processing
• Recognition Symbols
• docs/scan_workflow.md — the detailed reference