🔍 检查图片是不是 PNG（文件格式、损坏、APNG 检测）Check If Image Is PNG (Format, Corruption & APNG Check)

使用说明与常见问题How-to & FAQ

「检查图片是不是 PNG（文件格式、损坏、APNG 检测）」是什么？What is the Check If Image Is PNG (Format, Corruption & APNG Check) tool?

检查文件是不是真正的 PNG 图片：按文件头字节识别真实格式（扩展名改过的 JPG、WebP 等也能认出来），并逐个校验 PNG 数据块的 CRC，发现文件损坏、被截断、签名被改写或 IEND 后附加数据；同时显示尺寸、颜色类型、位深、透明、隔行扫描、APNG 动画帧数、DPI、色彩配置和文本信息。可一次检查多个文件，全部在浏览器本地完成，不上传。Check whether a file is really a PNG image. The tool identifies the true format from the file's header bytes (so it spots renamed JPGs, WebPs and more) and verifies the CRC of every PNG chunk to find damaged or cut-off files, a mangled signature, or data appended after IEND. It also shows the size, colour type, bit depth, transparency, interlacing, APNG frame count, DPI, colour profile and text fields. Check many files at once; everything runs locally in your browser and nothing is uploaded.

如何使用「检查图片是不是 PNG（文件格式、损坏、APNG 检测）」？How do I use the Check If Image Is PNG (Format, Corruption & APNG Check) tool?

在「检查图片是不是 PNG（文件格式、损坏、APNG 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 If Image Is PNG (Format, Corruption & APNG Check): Fill in or choose the options above and the result appears below instantly; everything runs locally in your browser.

怎么判断文件是不是 PNG？How does it tell whether a file is a PNG?

不看扩展名，而是读取文件开头的“魔数”字节：真正的 PNG 一定以 89 50 4E 47 0D 0A 1A 0A 这 8 个字节开头。不是 PNG 时会继续识别实际格式（JPEG、GIF、WebP、BMP、TIFF、ICO、AVIF、HEIC、JPEG XL、QOI、PSD、SVG、PDF、ZIP 等），所以能发现“扩展名是 .png、其实是 JPG”这类改名文件。It ignores the extension and reads the 'magic' bytes at the start of the file: a real PNG always begins with the 8 bytes 89 50 4E 47 0D 0A 1A 0A. If it isn't a PNG, the tool identifies the actual format (JPEG, GIF, WebP, BMP, TIFF, ICO, AVIF, HEIC, JPEG XL, QOI, PSD, SVG, PDF, ZIP and more), so it catches renamed files such as a JPG saved as .png.

“已损坏”是怎么检查出来的？How does it detect damage?

PNG 由一个个数据块（IHDR、IDAT、IEND 等）组成，每块都带 CRC 校验码。工具会重新计算每块的校验码并比对，任何一个字节出错都会报出所在的块；还会检查文件是否被截断（没下载完）、是否缺少结尾的 IEND、第一个块是不是 IHDR、位深与颜色类型的组合是否合法，以及 IEND 之后是否附加了多余数据。A PNG is made of chunks (IHDR, IDAT, IEND and so on), each with a CRC checksum. The tool recalculates every checksum, so a single wrong byte is reported along with the chunk it's in. It also checks whether the file is cut off (an unfinished download), whether the closing IEND is missing, whether the first chunk is IHDR, whether the bit depth and colour type are a valid pair, and whether extra data follows IEND.

APNG 和普通 PNG 有什么区别？How is APNG different from a normal PNG?

APNG（动态 PNG）是在普通 PNG 里加入 acTL 和 fcTL 数据块的动画格式，文件扩展名通常仍是 .png。不支持 APNG 的软件只会显示第一帧。工具会读取 acTL，显示总帧数和播放次数（0 表示无限循环）。APNG (animated PNG) adds acTL and fcTL chunks to a normal PNG to make an animation, and the extension is usually still .png. Software without APNG support just shows the first frame. The tool reads acTL to show the frame count and how many times it plays (0 means forever).

文件会上传吗？有大小限制吗？Are files uploaded? Is there a size limit?

不会上传，所有检查都在浏览器本地读取字节完成。一次最多检查 100 个文件；单个文件超过 300 MB 时只检查文件头，不做完整校验。No. All checks read the bytes locally in your browser. You can check up to 100 files at once; files over 300 MB only get a header check, not a full verification.

「检查图片是不是 PNG（文件格式、损坏、APNG 检测）」免费吗？需要注册吗？Is the Check If Image Is PNG (Format, Corruption & APNG Check) free? Do I need an account?

「检查图片是不是 PNG（文件格式、损坏、APNG 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 If Image Is PNG (Format, Corruption & APNG Check) is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.