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TIFF without XResolution/YResolution reports dpi (1, 1)

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已经有一个关联 PR 被合并了。

  • #10339 来自 @brettdavies —— 已合并

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2/5
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1-3 小时
新手友好度
75/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
python
领域
backend

调研方向

首先追踪 TIFF 插件如何将 XResolution、YResolution 和 ResolutionUnit 读入 im.info，然后与 issue 中提到的 PNG 和 JPEG 行为进行比较。为未包含分辨率标签而保存的 TIFF 添加或调整回归测试，并检查其 dpi 键不存在；保留包含分辨率标签的 TIFF 的预期行为。

由索引模型根据 Issue 内容生成。

描述

🤖-assisted TIFF
What did you do?

I'm building an image-optimization tool that prepares screenshots and photos for PDFs: it picks the output format, carries the DPI so pages place at the right size, and checks that lossless steps keep every pixel. Its test suite generates each input type Pillow opens and runs it through the tool, which is where this came up. A TIFF saved without resolution tags reported dpi == (1, 1), and the tool carried 1 DPI into its PNG and JPEG output, which a DPI-aware PDF tool would place at 96 inches wide for a 96-pixel image.

import io
from PIL import Image

buf = io.BytesIO()
Image.new("L", (16, 16)).save(buf, "TIFF")
with Image.open(buf) as im:
    print(im.tag_v2.get(282), im.tag_v2.get(283), im.tag_v2.get(296))
    print(im.info.get("dpi"), im.info.get("resolution"))
What did you expect to happen?

No dpi key, as for a PNG or JPEG saved without resolution.

What actually happened?
None None None
(1, 1) (1, 1)

xres = self.tag_v2.get(X_RESOLUTION, 1) and the same for Y supply 1 when the tags are absent. I understand this may be kept for compatibility; #10187 dropped BMP's (0, 0) placeholder in the same spirit.

Related: #10331 (JPEG dpi read from EXIF).

What are your OS, Python and Pillow versions?
  • OS: Ubuntu 24.04 (Linux x86_64)
  • Python: 3.13.13
  • Pillow: 13.0.0 (also reproduces on 12.3.0)
--------------------------------------------------------------------
Pillow 13.0.0
Python 3.13.13 (main, May 10 2026, 19:26:54) [Clang 22.1.3 ]
--------------------------------------------------------------------
Python executable is ~/.venv/bin/python
Environment Python files loaded from ~/.venv
System Python files loaded from ~/.local/share/uv/python/cpython-3.13.13-linux-x86_64-gnu
--------------------------------------------------------------------
Python Pillow modules loaded from ~/.venv/lib/python3.13/site-packages/PIL
Binary Pillow modules loaded from ~/.venv/lib/python3.13/site-packages/PIL
--------------------------------------------------------------------
--- PIL CORE support ok, compiled for 13.0.0
--- TKINTER support ok, loaded 9.0
--- FREETYPE2 support ok, loaded 2.14.3
--- LITTLECMS2 support ok, loaded 2.19
--- WEBP support ok, loaded 1.6.0
--- AVIF support ok, loaded 1.4.2
--- JPEG support ok, compiled for libjpeg-turbo 3.2.0
--- OPENJPEG (JPEG2000) support ok, loaded 2.5.4
--- ZLIB (PNG/ZIP) support ok, loaded 1.3, compiled for zlib-ng 2.3.3
--- LIBTIFF support ok, loaded 4.7.2
--- RAQM (Bidirectional Text) support ok, loaded 0.11.0, fribidi 1.0.13, harfbuzz 14.5.0
*** LIBIMAGEQUANT (Quantization method) support not installed
--- XCB (X protocol) support ok
--------------------------------------------------------------------
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