🌑 位图转灰度（导出 8 位灰度 BMP）Convert Bitmap to Grayscale
把位图（BMP）或其他图片转换成灰度：可选 ITU-R BT.601（常用的 0.299R + 0.587G + 0.114B）、BT.709（高清视频标准）、平均值、明度（最大值和最小值的平均），或直接取红、绿、蓝某一个通道，还可以反相。导出 BMP 时生成真正的 8 位灰度位图（256 级灰度调色板），文件只有 24 位 BMP 的约三分之一大；也可以导出 PNG 并保留透明。支持批量，图片只在浏览器本地处理。Convert a bitmap (BMP) or any other image to greyscale. Choose ITU-R BT.601 (the common 0.299R + 0.587G + 0.114B), BT.709 (the HD video standard), the average, lightness (mean of the largest and smallest channel), or a single red, green or blue channel, and optionally invert. BMP output is a true 8-bit greyscale bitmap with a 256-level grey palette, about a third the size of a 24-bit BMP; PNG output keeps transparency. Works in bulk, and images are processed locally in your browser.
使用说明与常见问题How-to & FAQ
「位图转灰度（导出 8 位灰度 BMP）」是什么？What is the Convert Bitmap to Grayscale tool?
把位图（BMP）或其他图片转换成灰度：可选 ITU-R BT.601（常用的 0.299R + 0.587G + 0.114B）、BT.709（高清视频标准）、平均值、明度（最大值和最小值的平均），或直接取红、绿、蓝某一个通道，还可以反相。导出 BMP 时生成真正的 8 位灰度位图（256 级灰度调色板），文件只有 24 位 BMP 的约三分之一大；也可以导出 PNG 并保留透明。支持批量，图片只在浏览器本地处理。Convert a bitmap (BMP) or any other image to greyscale. Choose ITU-R BT.601 (the common 0.299R + 0.587G + 0.114B), BT.709 (the HD video standard), the average, lightness (mean of the largest and smallest channel), or a single red, green or blue channel, and optionally invert. BMP output is a true 8-bit greyscale bitmap with a 256-level grey palette, about a third the size of a 24-bit BMP; PNG output keeps transparency. Works in bulk, and images are processed locally in your browser.
如何使用「位图转灰度（导出 8 位灰度 BMP）」？How do I use the Convert Bitmap to Grayscale tool?
在「位图转灰度（导出 8 位灰度 BMP）」中，选择或拖入文件，按需设置「灰度算法」、「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 Convert Bitmap to Grayscale: Choose or drop your files, set "Method", "Format", then click the Download button next to each result (with several files, "Download all (ZIP)" saves them together).
哪种灰度算法最好？Which method should I use?
一般照片用默认的 BT.601，它按人眼对绿色最敏感、蓝色最不敏感来加权，亮度最接近原图的感觉；BT.709 是高清视频和 sRGB 的标准，结果和 BT.601 很接近。“平均值”简单但蓝色会显得偏亮；“明度”对比较柔和；只取单个通道常用于突出某种颜色（例如用红色通道让天空变暗）。For photos the default BT.601 is best: it weights green most and blue least, matching how bright colours look to the eye. BT.709 is the HD-video and sRGB standard and gives very similar results. Average is simple but makes blue look too light; Lightness gives a softer contrast; a single channel is a classic darkroom trick to bring out certain colours (the red channel darkens a blue sky).
导出的灰度 BMP 是什么格式？What kind of BMP is produced?
导出 BMP 时是 8 位索引色位图：文件里有一张 256 级灰度调色板（0 = 黑 … 255 = 白），每个像素只占 1 个字节，所以比 24 位 BMP 小约三分之二，Windows 画图、Photoshop、GIMP、Python（Pillow 读作 L 或 P 模式）等都能直接打开。BMP 不支持透明，透明部分会填成白色；需要保留透明请导出 PNG。BMP output is an 8-bit indexed bitmap: it contains a 256-level grey palette (0 = black … 255 = white) and each pixel takes a single byte, so the file is about two thirds smaller than a 24-bit BMP. Windows Paint, Photoshop, GIMP and Python (Pillow reads it as mode L or P) open it directly. BMP has no transparency, so transparent areas are filled with white; 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.
「位图转灰度（导出 8 位灰度 BMP）」免费吗？需要注册吗？Is the Convert Bitmap to Grayscale free? Do I need an account?
「位图转灰度（导出 8 位灰度 BMP）」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 Convert Bitmap to Grayscale is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.