🔃 位图旋转（BMP 旋转 90° / 180° / 任意角度）Rotate a Bitmap

使用说明与常见问题How-to & FAQ

「位图旋转（BMP 旋转 90° / 180° / 任意角度）」是什么？What is the Rotate a Bitmap tool?

把位图（BMP）或其他图片旋转 90°、180°、270°（逐像素精确、无损），或旋转任意角度（-360° 到 360°，正数为顺时针）。任意角度时画布会自动扩大以完整显示旋转后的图片，空出的角落可以填背景色或保持透明（PNG）。默认导出 24 位 BMP，也可以导出 PNG，支持批量，图片只在浏览器本地处理。Rotate a bitmap (BMP) or any other image by 90°, 180° or 270° (exact and lossless, pixel for pixel), or by any angle from -360° to 360° (positive is clockwise). For any other angle the canvas grows so the whole rotated picture fits, and the empty corners are filled with a background colour or left transparent (PNG). The result is a 24-bit BMP by default, or PNG; works in bulk, and images are processed locally in your browser.

如何使用「位图旋转（BMP 旋转 90° / 180° / 任意角度）」？How do I use the Rotate a Bitmap tool?

在「位图旋转（BMP 旋转 90° / 180° / 任意角度）」中，选择或拖入文件，按需设置「旋转」、「角度（°）」、「背景色」、「输出格式」等选项，然后点击每个结果旁的「下载」按钮即可；有多个文件时也可以点「全部下载（ZIP）」一次打包下载。In the Rotate a Bitmap: Choose or drop your files, set "Rotation", "Angle (°)", "Background", "Format", then click the Download button next to each result (with several files, "Download all (ZIP)" saves them together).

90° 旋转和任意角度旋转有什么区别？How do 90° rotations differ from other angles?

90°、180°、270°（以及在“任意角度”里填写这些值）是逐像素重新排列，不插值、不改变任何颜色，转回去就完全和原图一样，宽高会对调（90°、270°）。其他角度必须插值计算每个新像素，边缘会有轻微的抗锯齿，画布会扩大到能完整放下旋转后的图片，四个角会空出来。90°, 180° and 270° (including those values typed under Any angle) simply rearrange pixels with no interpolation or colour change, so rotating back gives an identical image; width and height swap for 90° and 270°. Any other angle has to interpolate each new pixel, so edges get slight anti-aliasing, and the canvas grows to fit the whole rotated picture, leaving empty corners.

角度的方向和空白角落怎么处理？Which way does it turn, and what about the empty corners?

正数为顺时针、负数为逆时针，例如 -15 就是逆时针 15°。任意角度旋转后空出的角落默认填白色，可以改成其他背景色；导出 PNG 时勾选“透明背景”可以保持透明。BMP 不支持透明，所以总是填背景色。Positive angles turn clockwise and negative ones anticlockwise, so -15 turns 15° anticlockwise. The empty corners left by other angles are white by default — pick another background colour if you like — and with PNG output you can tick Transparent background to keep them clear. BMP has no transparency, so a background colour is always used.

导出的 BMP 是什么格式？What kind of BMP is produced?

默认导出 24 位不压缩 BMP（BITMAPINFOHEADER，自下而上存储），Windows 画图、Photoshop、GIMP、Python Pillow 和各种嵌入式工具都能直接打开。BMP 不支持透明，透明部分会填成白色并在结果里提示；需要保留透明请导出 PNG。By default a 24-bit uncompressed BMP (BITMAPINFOHEADER, stored bottom-up), which Windows Paint, Photoshop, GIMP, Python Pillow and embedded tools open directly. BMP has no transparency, so transparent areas are filled with white (the result says so); export PNG to keep transparency.

支持哪些图片？会上传吗？Which images work, and are they uploaded?

支持 JPG、PNG、WebP、GIF（静态或动图的第一帧）、BMP、AVIF、HEIC，以及浏览器能打开的 SVG；可一次拖入最多 50 张批量处理，单张最大 60 MB、1 亿像素；多张结果可打包成 ZIP 下载。所有处理都在你的浏览器里完成，图片不会上传，结果中也不会保留 EXIF 等元数据（包括拍摄位置）。JPG, PNG, WebP, GIF (a still or the first frame of an animation), BMP, AVIF, HEIC, and SVG that the browser can open. Drop in up to 50 images at once; each can be up to 60 MB and 100 megapixels, and several results can be downloaded as a ZIP. Everything happens in your browser: images are not uploaded, and EXIF and other metadata (including location) is not kept in the results.

「位图旋转（BMP 旋转 90° / 180° / 任意角度）」免费吗？需要注册吗？Is the Rotate a Bitmap free? Do I need an account?

「位图旋转（BMP 旋转 90° / 180° / 任意角度）」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Rotate a Bitmap is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.