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feat(detector): recurse into Form XObjects for image detection and classify vector-text pages

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Images nested inside Form XObjects (e.g. HuttoISDWorkPerks.pdf) were
invisible to the detector. Rewrote analyze_page_images to recursively
follow Form XObjects. Also added pages_with_vector_text tracking so
PDFs with vector-outlined text (e.g. qsop_21-0055.pdf) are correctly
classified as IMAGE-BASED with OCR recommended.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Abimael Martell
2026-03-09 21:12:25 -07:00
co-authored by Claude Opus 4.6
parent c1357e79ea
commit ea4709517e
1 changed files with 117 additions and 53 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/detector.rs
+117 -53
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@@ -186,6 +186,7 @@ pub(crate) fn detect_from_document(
let mut pages_with_text = 0u32;
let mut pages_with_images = 0u32;
let mut pages_with_template_images = 0u32;
let mut pages_with_vector_text = 0u32;
let mut total_text_ops = 0u32;
// Cache Phase 1 results to avoid re-analyzing sampled pages in Phase 2
let mut analysis_cache: HashMap<u32, PageAnalysis> = HashMap::new();
@@ -195,6 +196,13 @@ pub(crate) fn detect_from_document(
if let Some(&page_id) = pages.get(page_num) {
let analysis = analyze_page_content(doc, page_id);
pages_actually_sampled += 1;
log::debug!(
"page {}: text_ops={} images={} image_count={} template={} unique_chars={} path_ops={} vector_text={} image_area={}",
page_num, analysis.text_operator_count, analysis.has_images,
analysis.image_count, analysis.has_template_image,
analysis.unique_text_chars, analysis.path_op_count, analysis.has_vector_text,
analysis.total_image_area
);
let is_image_dominated = analysis.image_count > 10
&& analysis.image_count > analysis.text_operator_count * 3;
let effective_min_ops = if analysis.has_images || analysis.image_count > 0 {
@@ -215,6 +223,9 @@ pub(crate) fn detect_from_document(
if analysis.has_template_image {
pages_with_template_images += 1;
}
if analysis.has_vector_text {
pages_with_vector_text += 1;
}
total_text_ops += analysis.text_operator_count;
analysis_cache.insert(*page_num, analysis.clone());
@@ -261,14 +272,15 @@ pub(crate) fn detect_from_document(
} else if text_ratio >= config.text_page_ratio_threshold {
ocr_recommended = false;
(PdfType::TextBased, text_ratio)
} else if pages_with_text == 0 && pages_with_images > 0 {
} else if pages_with_text == 0 && (pages_with_images > 0 || pages_with_vector_text > 0) {
// No extractable text but has images or vector-outlined text
ocr_recommended = true;
if total_text_ops == 0 {
if total_text_ops == 0 && pages_with_vector_text == 0 {
(PdfType::Scanned, 0.95)
} else {
(PdfType::ImageBased, 0.8)
}
} else if pages_with_text > 0 && pages_with_images > 0 {
} else if pages_with_text > 0 && (pages_with_images > 0 || pages_with_vector_text > 0) {
ocr_recommended = true;
(PdfType::Mixed, 0.7)
} else if total_text_ops == 0 {
@@ -767,6 +779,7 @@ fn analyze_page_images(doc: &Document, page_id: ObjectId) -> (bool, u64, bool) {
let mut has_images = false;
let mut total_area: u64 = 0;
let mut has_template_image = false;
let mut visited: HashSet<ObjectId> = HashSet::new();
if let Ok(page_dict) = doc.get_dictionary(page_id) {
let resources = match page_dict.get(b"Resources") {
@@ -776,62 +789,113 @@ fn analyze_page_images(doc: &Document, page_id: ObjectId) -> (bool, u64, bool) {
};
if let Some(resources) = resources {
if let Ok(xobject) = resources.get(b"XObject") {
let xobject_dict = match xobject {
Object::Reference(id) => doc.get_dictionary(*id).ok(),
Object::Dictionary(dict) => Some(dict),
_ => None,
};
if let Some(xobject_dict) = xobject_dict {
for (_, value) in xobject_dict.iter() {
if let Ok(xobj_ref) = value.as_reference() {
if let Ok(xobj) = doc.get_object(xobj_ref) {
if let Ok(stream) = xobj.as_stream() {
// Check if it's an Image subtype
if let Ok(subtype) = stream.dict.get(b"Subtype") {
if let Ok(name) = subtype.as_name() {
if name == b"Image" {
has_images = true;
// Get image dimensions
let width = stream
.dict
.get(b"Width")
.ok()
.and_then(|w| w.as_i64().ok())
.unwrap_or(0)
as u64;
let height = stream
.dict
.get(b"Height")
.ok()
.and_then(|h| h.as_i64().ok())
.unwrap_or(0)
as u64;
let area = width * height;
total_area += area;
// Check if this is a large template image
if area >= TEMPLATE_IMAGE_THRESHOLD {
has_template_image = true;
}
}
}
}
}
}
}
}
}
}
collect_images_from_resources(
doc,
resources,
&mut has_images,
&mut total_area,
&mut has_template_image,
TEMPLATE_IMAGE_THRESHOLD,
&mut visited,
);
}
}
(has_images, total_area, has_template_image)
}
/// Recursively collect image dimensions from XObject resources,
/// including images nested inside Form XObjects.
fn collect_images_from_resources(
doc: &Document,
resources: &lopdf::Dictionary,
has_images: &mut bool,
total_area: &mut u64,
has_template_image: &mut bool,
threshold: u64,
visited: &mut HashSet<ObjectId>,
) {
let xobject = match resources.get(b"XObject") {
Ok(obj) => obj,
_ => return,
};
let xobject_dict = match xobject {
Object::Reference(id) => doc.get_dictionary(*id).ok(),
Object::Dictionary(dict) => Some(dict),
_ => None,
};
let Some(xobject_dict) = xobject_dict else {
return;
};
for (_, value) in xobject_dict.iter() {
let xobj_ref = match value.as_reference() {
Ok(r) => r,
_ => continue,
};
if !visited.insert(xobj_ref) {
continue;
}
let xobj = match doc.get_object(xobj_ref) {
Ok(o) => o,
_ => continue,
};
let stream = match xobj.as_stream() {
Ok(s) => s,
_ => continue,
};
let subtype = match stream.dict.get(b"Subtype") {
Ok(s) => s,
_ => continue,
};
let name = match subtype.as_name() {
Ok(n) => n,
_ => continue,
};
if name == b"Image" {
*has_images = true;
let width = stream
.dict
.get(b"Width")
.ok()
.and_then(|w| w.as_i64().ok())
.unwrap_or(0) as u64;
let height = stream
.dict
.get(b"Height")
.ok()
.and_then(|h| h.as_i64().ok())
.unwrap_or(0) as u64;
let area = width * height;
*total_area += area;
if area >= threshold {
*has_template_image = true;
}
} else if name == b"Form" {
// Recurse into Form XObject's own Resources
if let Ok(form_resources) = stream.dict.get(b"Resources") {
let form_res_dict = match form_resources {
Object::Reference(id) => doc.get_dictionary(*id).ok(),
Object::Dictionary(dict) => Some(dict),
_ => None,
};
if let Some(form_res) = form_res_dict {
collect_images_from_resources(
doc,
form_res,
has_images,
total_area,
has_template_image,
threshold,
visited,
);
}
}
}
}
}
/// Get document title from Info dictionary
fn get_document_title(doc: &Document) -> Option<String> {
let info_ref = doc.trailer.get(b"Info").ok()?.as_reference().ok()?;