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Canva MCPで日本語タイトルが「天久百厳浸」になった — AI生成の限界と代替手順の記録

#mcp #python #ai #claude

Canva MCP Generated "天久百厳浸" Instead of My Japanese Title — Failure Log

I called Canva MCP from Claude Code to generate hero images with Japanese titles. All 4 generated images had random kanji characters ("天久百厳浸", "米岡済本") that had nothing to do with my actual title.

Root Cause

Canva's AI image generation engine is trained primarily on English corpora and cannot preserve the semantic meaning of Japanese text when rendering it visually.

Operation Japanese Text Handling
generate-design (AI generation) Random kanji output
Template copy + text edit Works correctly

The Fix: Pillow + Bundled TTF Fonts 

from PIL import ImageFont, ImageDraw, Image

# Bundle TTF in the repo — don't rely on system fonts
title_font = ImageFont.truetype("public/fonts/NotoSansJP-Bold.ttf", size=48)
sub_font   = ImageFont.truetype("public/fonts/NotoSansJP-Regular.ttf", size=24)
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Key insight: System font dependencies (like IPAGothic) break in cloud environments. Bundling fonts in the repo makes the pipeline reproducible.

Decision Framework

"Is this tool trained on English corpora?"

  • YES → Don't trust it for Japanese content semantic integrity
  • NO or local processing (Pillow, ImageMagick) → Fine

"Is this running in an automated pipeline without human review?"

  • YES → Don't use AI-generated text for Japanese content

Full failure log (in Japanese) at masatoman.net.

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