Latex PDF Preprocess

LaTeX PDF Figure Preprocessing

Fix PDF figures (especially from Adobe Illustrator) so they embed cleanly in xelatex.

The problem

Adobe Illustrator exports PDFs with ICC-based color profiles as indirect stream references inside page-level transparency groups. xdvipdfmx (xelatex's PDF backend) crashes on these:

Assertion failed: (!indirect->pf), function write_indirect, file pdfobj.c

The fix

Replace the ICC color space reference in the page-level transparency /Group with /DeviceRGB. This is a single metadata swap — no rasterization, no PostScript roundtrip, no content changes. Transparency and blending are fully preserved.

Core Command

import pikepdf, sys

pdf = pikepdf.open(sys.argv[1])
for page in pdf.pages:
    if "/Group" in page:
        g = page["/Group"]
        if "/CS" in g and isinstance(g["/CS"], pikepdf.Array):
            g["/CS"] = pikepdf.Name("/DeviceRGB")
pdf.save(sys.argv[2])

Usage:

python3 fix_pdf.py input.pdf output.pdf

Batch Processing

import pikepdf, os

for d in sorted(os.listdir("figures")):
    fpath = os.path.join("figures", d, "figure.pdf")
    if not os.path.isfile(fpath):
        continue
    pdf = pikepdf.open(fpath)
    fixed = False
    for page in pdf.pages:
        if "/Group" in page:
            g = page["/Group"]
            if "/CS" in g and isinstance(g["/CS"], pikepdf.Array):
                g["/CS"] = pikepdf.Name("/DeviceRGB")
                fixed = True
    if fixed:
        tmp = fpath + ".tmp"
        pdf.save(tmp)
        pdf.close()
        os.replace(tmp, fpath)
        print(f"Fixed: {d}")
    else:
        pdf.close()
        print(f"OK:    {d} (no ICC group)")

Dependencies

pip install pikepdf

Verifying the Output

# Page dimensions should be identical
pdfinfo input.pdf | grep 'Page size'
pdfinfo output.pdf | grep 'Page size'

Or confirm the fix programmatically:

import pikepdf
pdf = pikepdf.open("output.pdf")
for page in pdf.pages:
    if "/Group" in page and "/CS" in page["/Group"]:
        cs = page["/Group"]["/CS"]
        assert cs == pikepdf.Name("/DeviceRGB"), f"Still ICC: {cs}"
print("OK")

Cropping whitespace

PDF figures (especially from Illustrator) often have excess whitespace from the artboard being larger than the artwork. Use pdfcrop (ships with TeX Live) to trim to content bounds:

pdfcrop --margins 2 input.pdf output.pdf

The --margins value is in bp (1bp = 1/72 inch). A small margin (1–2bp) prevents clipping artifacts at content edges.

Batch crop:

for f in figures/*.pdf; do
    pdfcrop --margins 2 "$f" "${f%.pdf}_cropped.pdf" && mv "${f%.pdf}_cropped.pdf" "$f"
done

What this does NOT do

• Does not rasterize anything — vectors, images, and text are untouched
• Does not change PDF version
• Does not flatten transparency — blending modes and opacity are preserved
• Does not touch Form XObject groups (only the page-level group needs fixing)

Background

The page-level /Group dictionary controls the transparency blending color space for the entire page. Illustrator sets this to [/ICCBased <stream>] where the stream is an embedded sRGB ICC profile. xdvipdfmx crashes when it encounters this indirect stream reference during PDF output. Replacing it with the equivalent /DeviceRGB name avoids the indirect reference while preserving identical color behavior (the ICC profile is sRGB).