PDF 转图片
把每一页渲染为 JPG、PNG 或 WebP。
这款工具完全在你的浏览器中运行。文件从不上传，你可以在浏览器的网络标签中亲自验证这一点。 亲自验证：打开浏览器的网络标签观察。你会看到一个查询你是否还有剩余任务的小请求，只包含工具名称和一段哈希，绝不会包含文件。
这款工具的作用
Each page is redrawn as a grid of pixels at the resolution you choose and saved as a JPG, PNG or WebP. Because the page is rendered rather than exported, what you get is a picture of the page: text stops being text, and nothing in the image can be selected, searched or edited afterwards.
Reach for it when something needs a picture rather than a document: a page to drop into a slide, a diagram for a chat app that will not preview a PDF, or a proof for a print shop that asked for images at 300 dpi.
工作原理
- Drop the PDF onto this page. One file at a time, up to 300 MB.
- Pick the format. JPEG suits scans and photographs, PNG suits text, diagrams and flat colour.
- Set the resolution. 150 dpi is comfortable on a screen and 300 dpi is what a printer wants.
- Give a page range if you only want part of the document, or leave it empty for every page.
- Under advanced options, switch to grayscale or ask for a transparent background.
- Press Convert to images. Each page arrives as its own file, and a ZIP is offered when there is more than one.
Resolution is the one decision here that really costs something. Doubling the DPI quadruples the pixel count: an A4 page at 150 dpi is about 2 megapixels, the same page at 600 dpi about 35. So each page is held to a ceiling of 40 megapixels and the scale is stepped down until it fits, and the result reports the resolution actually used - a request for 600 dpi that came back as 410 explains itself rather than turning up later as a soft print.
The three formats fail in different directions. JPEG is lossy and compresses photographic scans far better than anything else, but it smears the edges of small text; the quality slider runs from 40 to 100 and sits at 90, near the point where more quality mostly buys more bytes. PNG is lossless and keeps text and line art crisp, often at several times the size. WebP beats both at a similar quality, at the cost of older software that refuses to open it.
The conversion is one-way. Nothing in the image knows it was ever text, so a converted page cannot be searched or copied from, and running the images back through Image to PDF gives you a document of pictures rather than the file you started with. If you want the words, use PDF to text; if the problem is only that the file is too big to send, Compress PDF keeps the text alive in it.
Rendering happens on an OffscreenCanvas in a Web Worker, using the same PDF.js engine your browser uses to preview a PDF. Nothing is uploaded at any size, and once this page has loaded the tool keeps working with the network off. Files are numbered with leading zeros sized to the page count, so a 120-page document produces 001 through 120 and sorts correctly everywhere.
这款工具做不到的事
- The output is pixels. Text inside the images cannot be selected, searched or edited, and no reader will find a word in them.
- Very large pages are rendered below the resolution you asked for, because each page is held to a 40-megapixel ceiling. The result shows the resolution actually used.
常见问题
- 我该选多少 DPI？
- 屏幕上阅读用 150 dpi，打印用 300 dpi，而当图片应当匹配页面定义的尺寸时用 72 dpi。更高并不自动更好：数值翻倍会让文件大小变成四倍，而超过 300 dpi 后，除非原件是高分辨率扫描，多出来的细节通常看不出来。
- JPG、PNG 还是 WebP——选哪个？
- 扫描件和照片用 JPG，它小得多，而损失也很难看出来。文字、图表和截图用 PNG，因为有损压缩会让小字母的边缘变模糊。当你能掌控由什么来打开文件、又想让它比前两者都小时，就用 WebP。
- 我可以只转换其中一部分页面吗？
- 可以。输入像 1-4 这样的范围，或 2, 5, 9-，或者 odd、even 和 last 这些词；留空则是全部页面。每一页都会成为自己的图片，当有多张时，你可以把它们全部作为一个 ZIP 取走。
- 我能得到透明背景的图片吗？
- 选择 PNG，并在高级选项中把背景设为透明。JPEG 不提供这个选项，因为它根本没有透明通道。请注意，一个自己绘制了白色矩形的页面——很多都会——仍然会是白色的，因为那个矩形是页面内容，而不是它后面的背景。
- 我的 PDF 会被上传到什么地方吗？
- 不会。页面在 Web Worker 中渲染，图片从不离开设备。你可以核实这一点，而不必凭信任：打开开发者工具，切换到网络标签，转换一个文件。什么都不会被发送，而且这款工具在断网时也能使用。