🔲 检查图片是否透明（透明像素、Alpha 通道检测）Check Image Transparency (Alpha Channel & Transparent Pixels)

使用说明与常见问题How-to & FAQ

「检查图片是否透明（透明像素、Alpha 通道检测）」是什么？What is the Check Image Transparency (Alpha Channel & Transparent Pixels) tool?

检查图片有没有透明背景：逐像素统计完全透明、半透明和不透明像素的比例，读取文件头判断格式是否带透明通道（PNG Alpha / tRNS、GIF 透明色、WebP Alpha），给出可见内容的范围（可据此裁掉透明边），并发现“带透明通道但其实没用到”的图片。支持 PNG、WebP、GIF、AVIF、BMP、JPG 等，可批量检查，图片只在浏览器本地处理。Find out whether an image has a transparent background. The tool counts fully transparent, semi-transparent and opaque pixels, reads the file header to see whether the format carries transparency (PNG alpha or tRNS, GIF transparent colour, WebP alpha), reports the visible content box (handy for trimming transparent margins), and flags images that have a transparency channel they never use. Works with PNG, WebP, GIF, AVIF, BMP, JPG and more, in batches. Images are processed locally in your browser.

如何使用「检查图片是否透明（透明像素、Alpha 通道检测）」？How do I use the Check Image Transparency (Alpha Channel & Transparent Pixels) tool?

在「检查图片是否透明（透明像素、Alpha 通道检测）」中，在上方填写或选择所需内容，结果会实时显示在下方；所有处理都在浏览器本地完成。In the Check Image Transparency (Alpha Channel & Transparent Pixels): Fill in or choose the options above and the result appears below instantly; everything runs locally in your browser.

怎么判断图片是否透明？How does it decide whether an image is transparent?

工具同时做两项检查：一是读取文件头，看格式本身有没有透明通道（PNG 的 Alpha 或 tRNS、GIF 的透明色、WebP 的 Alpha 标志；JPG 不支持透明）；二是解码后逐个像素读取透明度，统计完全透明（A = 0）、半透明（0 < A < 255）和不透明像素各占多少。结论以实际像素为准。It does two checks. First it reads the file header to see whether the format carries transparency at all (PNG alpha or tRNS, the GIF transparent colour, the WebP alpha flag; JPG has none). Then it decodes the image and reads every pixel's alpha, counting fully transparent (A = 0), semi-transparent (0 < A < 255) and opaque pixels. The verdict is based on the actual pixels.

“带透明通道但没有用到”是什么意思？What does 'has a transparency channel but doesn't use it' mean?

很多 PNG 以 RGBA 格式保存，但每个像素都是完全不透明的，比如截图或导出时默认带了 Alpha。这种图片看起来与不透明图片完全一样，转成 JPG 或去掉 Alpha 通道不会改变外观，还能减小文件体积。Many PNGs are saved as RGBA even though every pixel is fully opaque, for example screenshots or exports that add alpha by default. They look exactly like an opaque image, so converting to JPG or dropping the alpha channel won't change how they look and can make the file smaller.

“可见内容范围”有什么用？What is the visible content box for?

它是所有非完全透明像素的最小外框（左上角坐标和宽高）。比外框大的部分都是透明边，可以按这个范围裁剪图片，去掉多余的透明留白，让图标、贴纸和抠图后的商品图更紧凑。It's the smallest rectangle (top-left corner, width and height) that holds every pixel that isn't fully transparent. Anything outside it is transparent margin, so you can crop to that box to remove empty space and make icons, stickers and cut-out product shots tighter.

支持哪些格式？会上传吗？Which formats work? Is anything uploaded?

支持 PNG、WebP、GIF（检查第一帧）、AVIF、BMP、HEIC 和 JPG，一次最多 50 张，单张最大 60 MB。所有检查都在浏览器本地完成，图片不会上传。PNG, WebP, GIF (first frame), AVIF, BMP, HEIC and JPG are supported, up to 50 images at once and 60 MB each. All checks run locally in your browser and images are never uploaded.

「检查图片是否透明（透明像素、Alpha 通道检测）」免费吗？需要注册吗？Is the Check Image Transparency (Alpha Channel & Transparent Pixels) free? Do I need an account?

「检查图片是否透明（透明像素、Alpha 通道检测）」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 Check Image Transparency (Alpha Channel & Transparent Pixels) is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.