page.get_images() only returns raster blobs embedded in the PDF's
resource dictionary, so vector schematics like Figure 1 — drawn purely
with paths/lines — were never extracted, and the VLM only ever saw
incidental embedded photos that happened to live near figures.
Replace the xref-based extraction with bbox rendering: union the
bounding rects of all vector drawings and raster image_info entries on
each page, expand a few points, and render the region with
get_pixmap(clip=bbox, matrix=2x). The captioner now receives the
actual figure — schematic arrows, box labels, legend text, and any
inset photos — and produces a caption that describes the figure as a
whole, not just one embedded sub-image.
Also sharpen the captioner prompt: explicitly tell the VLM the image
is a single figure cropped from a PDF page, and not to describe page
chrome or body paragraphs.
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