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M6: detect form fields on scanned pages (#1721) (#1722)

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Field detection read only vector data: text-layer words and drawn
rectangles and lines. A scanned form is a single picture, so it found
nothing there.

A page that an image covers at least half of, and whose content draws
no lines, is now rendered at 144 dpi and its shapes are read from the
pixels (pdfcraft_forms::detect::raster): ink against a local mean,
long thin runs as lines, enclosed rectangular patches of paper as
boxes, the empty band of a box with a small printed label as its
writing area, and the open-ended horizontal lines as rules. Labels come
from the text layer, else from OCR when the models are installed;
without either the fields get default names. Detection works in the
displayed frame, so a scan stored sideways reads like any other, and
fields on a turned page get /MK /R so typing reads upright.

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This commit is contained in:
alexanderalber
2026-10-15 02:21:42 -04:00
committed by GitHub
parent 659c8fcbd4
commit 5b220eb886
8 changed files with 893 additions and 21 deletions
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parity/acrobat-features.toml
+2 -2
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@@ -5064,8 +5064,8 @@ milestone = "M6"
status = "partial"
commands = ["form.detect", "form.prepare"]
tools = ["form_detect_fields"]
evidence = ["crates/forms/src/tests.rs::detection_finds_blanks_rules_boxes_and_names_them", "crates/engine/src/tests.rs::detecting_fields_on_a_printed_form", "crates/automation/tests/automation.rs::detecting_form_fields_through_tools", "crates/ui-egui/tests/javascript.rs::prepare_a_form_detects_fields_on_a_paper_form", "crates/ui-egui/tests/prepare.rs::deleting_several_selected_fields_and_detecting_fields_from_the_panel"]
notes = "Underscore runs, rules, empty boxes and small squares (check boxes); runs when Prepare a form starts on a document without fields, and from Prepare a form ▸ Detect form fields at any time (existing fields are skipped). Not yet: comb boxes, tables of cells, scanned forms (needs OCR first), radio groups."
evidence = ["crates/forms/src/tests.rs::detection_finds_blanks_rules_boxes_and_names_them", "crates/engine/src/tests.rs::detecting_fields_on_a_printed_form", "crates/engine/src/tests.rs::detecting_fields_on_a_scanned_form", "crates/forms/src/detect/raster.rs::a_scanned_form_gives_its_rules_boxes_and_check_boxes", "crates/forms/src/detect/raster.rs::noise_and_uneven_paper_do_not_hide_the_lines", "crates/automation/tests/automation.rs::detecting_form_fields_through_tools", "crates/ui-egui/tests/javascript.rs::prepare_a_form_detects_fields_on_a_paper_form", "crates/ui-egui/tests/prepare.rs::deleting_several_selected_fields_and_detecting_fields_from_the_panel"]
notes = "Underscore runs, rules, empty boxes and small squares (check boxes); runs when Prepare a form starts on a document without fields, and from Prepare a form ▸ Detect form fields at any time (existing fields are skipped). Scanned pages (an image covers at least half the page and the content draws no lines) are rendered and their rules, boxes and check boxes read from the pixels; a box with a small printed label gets a field in its empty part. Tested on synthetic scans only: straight, stored sideways with /Rotate 90 (fields get /MK /R so typing reads upright), noisy, and 1 degree askew (fields stay inside their boxes but lose up to the skew in height). Labels come from the text layer or, when the OCR models are installed, from text recognition (Latin without accents, so German labels with umlauts make poorer names); without either, fields get default names (Text1, Check Box1). Recognition runs synchronously, about a second per scanned page. Not yet: comb boxes, dotted leader lines, tables of cells as such, deskewing, radio groups."
[[feature]]
id = "form.auto-name-fields"