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86 lines
4.1 KiB
Markdown
86 lines
4.1 KiB
Markdown
# Doubao visible watermark capture
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> **Status (captured 2026-05-29; asset rebuilt 2026-05-31):** the
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> black and gray captures are committed here. The generated alpha
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> asset is now a detection silhouette and mask-shaping input only. Current
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> removal localizes the mark and sends its footprint to the shared fill backend.
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> Reverse-alpha recovery was retired. The details below preserve the historical
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> capture rationale.
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Goal: capture the Doubao "豆包AI生成" visible watermark over known flat backgrounds so we can
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rebuild and validate the detection silhouette used by
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`src/remove_ai_watermarks/doubao_engine.py`.
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## Historical findings from the capture work
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- Blend model: **alpha compositing with a white logo** `watermarked = a*logo + (1-a)*original`,
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`logo = (255,255,255)`. Inversion: `original = (watermarked - a*logo) / (1-a)`.
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Confirmed by two independent sources (an open-source remover's algorithm doc + aiwatermarkremover.dev,
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both say "alpha map"). One commercial blog (pixelcleanai) claims "screen blend" instead; the gray
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capture below settles it empirically.
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- Position: **bottom-right corner**, small margins (right ~8-20px, bottom ~5px), scales with image size.
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Confirmed by our sample `data/fixtures/provenance/doubao-1.png` (2048x2048) plus three sources.
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- Size **scales with resolution**. Third-party numbers (~90x18 at <=1024, ~180x40 at >1024) are
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approximate and calibrated for ~1024-1280 outputs; at 2048 the strip is much larger. A shipped
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third-party alpha map is only 120x20, too small for our 2K/4K target -> capture fresh.
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- The original implementation used reverse-alpha recovery. That path was later
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removed in favor of localize then fill because the latter also handles moved
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and re-rendered marks.
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## Use doubao.com specifically
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The "豆包AI生成" mark is Doubao's. Jimeng / Dreamina use a different mark. Generate on doubao.com so
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the captured template matches our target.
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## How to capture (image-edit path, most reliable)
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For each locally generated solid-color seed:
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1. Open Doubao image generation, use the image-edit / reference mode, upload the seed.
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2. Prompt (Chinese preferred):
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`请完全按照原图重新生成这张图片，保持完全一致，不要添加或修改任何内容`
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(English: `Recreate this image exactly as it is, keep it identical, do not add or change anything`)
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3. Download the ORIGINAL output file (not a screenshot). Do not crop / edit / re-save.
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Prior art confirms uploading a pure-black image and letting Doubao stamp it works.
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If edit mode is unavailable and text-to-image refuses a solid color, fall back to generating 10-12
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normal-content images at one fixed resolution; the mark is the only constant across them and can be
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extracted by per-pixel min/median.
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## What to capture (priority top to bottom)
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| Aspect | black | white | gray128 | why |
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|--------|-------|-------|---------|-----|
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| 1:1 | 3 | 1 | 1 | primary alpha map + confirm the stamp is pixel-identical across runs + settle blend mode |
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| 16:9 | 2 | 1 | 1 | anchor rule in landscape |
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| 9:16 | 2 | 1 | 1 | anchor rule in portrait |
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| 4:3, 3:4 | 1 each | - | - | optional, refines anchor rule |
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- 3 blacks on 1:1: if the first two are byte-identical in the watermark region, the third is optional.
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- gray128 is the blend-mode test: predict the gray result from the black capture under alpha vs screen;
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whichever matches the real gray output is the true blend.
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- If the UI offers multiple output resolutions (1K / 2K / 4K), capture one black per resolution on 1:1 -
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needed to learn how the watermark scales.
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- Also grab 3-5 normal-content images on 1:1 for end-to-end removal validation.
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## Hygiene
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- Original download, never a screenshot. PNG preferred; if Doubao only gives JPEG, note it.
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- No crop / edit / re-save. Default settings, watermark left ON.
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## Committed inputs
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```
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doubao_black_1x1_1.png
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doubao_gray_1x1_1.png
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```
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The black and gray captures feed `scripts/visible_alpha_solve.py doubao`.
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## Also report back
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1. Which resolutions and aspect ratios the Doubao UI actually offers.
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2. Whether there is a watermark on/off toggle in the UI.
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3. Download format (PNG or JPEG).
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