Photo to cyanotype print: Qwen Image edit or a Pillow colorize?

A cyanotype is a two-tone image, white highlights on Prussian blue, so you can make one from any photo with Pillow alone: grayscale, autocontrast, then ImageOps.colorize with a dark blue black point and a pale blue-white white point. That costs nothing. Use an image model, qwen/qwen-image at $0.025 per image in the Sume catalog I read, only when you want what Pillow cannot add: uneven brush edges, a paper border and visible exposure streaks.

What does the free Pillow route give me?

A clean, even, digital cyanotype. The mapping is deterministic, so every photo in a batch gets the same two inks. It will not invent a hand-coated border or fibre texture, which is why people reach for an edit model.

Pick the two colors once and reuse them. The script below also loops over a folder so a set of photos stays consistent.

from pathlib import Path
from PIL import Image, ImageOps

INK = "#0b2a5b"    # deep Prussian blue
PAPER = "#e8f1fb"  # pale blue-white

Path("cyano").mkdir(exist_ok=True)
for src in Path("photos").glob("*.jpg"):
    gray = ImageOps.grayscale(Image.open(src))
    gray = ImageOps.autocontrast(gray, cutoff=2)
    out = ImageOps.colorize(gray, black=INK, white=PAPER)
    out.save(Path("cyano") / f"{src.stem}.png")
    print("wrote", src.stem)

When is the Qwen edit worth the 2.5 cents?

When the print should look hand-made. Send the photo as one input_references entry to qwen/qwen-image and ask for a cyanotype with a rough brushed border and visible paper fibre. Sume's catalog lists this row as edit-capable with up to 10 references, PNG, JPEG or WebP output, and 1 to 4 images per call. It has no quality or resolution field, so a request that sends one gets 400 unsupported_parameter.

The aspect list for this row has no auto value, so pin the ratio yourself: 3:4 for a portrait photo, 4:3 for landscape. Sume's docs warn that leaving the field off on an edit is not the same as auto, and this row does not offer auto to begin with.

Should I run both?

Yes, if the edit comes back with a greenish or purple blue. Run the model's output through the same colorize step to force your two inks, and keep its texture. Qwen's own newer checkpoint, Qwen-Image-2.1-Turbo, is described on its model card as a 7B model that runs in 8 steps, but Sume does not say which Qwen version its qwen/qwen-image row runs, so judge it on the output, not the model card.

If a request exceeds the 30-second wait it returns 202; read the picture from the job result as described in Jobs and results.