[Bug report] Lossless WebP Size is not correct

[poppingmoon]

Version

2.1.2

Platforms

dart

Device Model

any

flutter info

[√] Flutter (Channel stable, 3.19.4, on Microsoft Windows [Version 10.0.22631.3296], locale ja-JP)
    • Flutter version 3.19.4 on channel stable at C:\Users\thkt3\fvm\versions\stable
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 68bfaea224 (10 days ago), 2024-03-20 15:36:31 -0700
    • Engine revision a5c24f538d
    • Dart version 3.3.2
    • DevTools version 2.31.1

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
    • Android SDK at C:\Users\thkt3\AppData\Local\Android\sdk
    • Platform android-34, build-tools 33.0.0
    • Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
    • Java version OpenJDK Runtime Environment (build 17.0.7+0-b2043.56-10550314)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Build Tools 2022 17.9.2)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools
    • Visual Studio Build Tools 2022 version 17.9.34622.214
    • Windows 10 SDK version 10.0.22000.0

[√] Android Studio (version 2023.1)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.7+0-b2043.56-10550314)

[√] VS Code (version 1.87.2)
    • VS Code at C:\Users\thkt3\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.84.0

[√] Connected device (4 available)
    • Pixel 7a (mobile) • 192.168.151.7:40979 • android-arm64  • Android 14 (API 34)
    • Windows (desktop) • windows             • windows-x64    • Microsoft Windows [Version 10.0.22631.3296]
    • Chrome (web)      • chrome              • web-javascript • Google Chrome 123.0.6312.60
    • Edge (web)        • edge                • web-javascript • Microsoft Edge 123.0.2420.65

[√] Network resources
    • All expected network resources are available.

• No issues found!

How to reproduce?

Getting size of lossless WebP using ImageSizeGetter.getSize() returns irrelevant value.

For example, with https://raw.githubusercontent.com/poppingmoon/dart_image_size_getter/webp-lossless/example/asset/demo_lossless.webp as input, ImageSizeGetter.getSize() returns Size( 19512, 18715, needRotate: false ), which is different from actual size (988, 466).

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Example code (optional)

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Contact

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