📄 PPM 转 PDF（支持 PGM / PBM / PAM）PPM to PDF Converter

使用说明与常见问题How-to & FAQ

「PPM 转 PDF（支持 PGM / PBM / PAM）」是什么？What is the PPM to PDF Converter tool?

把 Netpbm 图片（PPM 彩色、PGM 灰度、PBM 黑白、PAM）转换成 PDF：支持 P1–P7 文本和二进制格式、16 位深度和一个文件里连续存放的多张图，每张一页，无损写入，可选 A4 / Letter 排版，全部在浏览器本地完成。Turn Netpbm images — PPM colour, PGM greyscale, PBM black-and-white and PAM — into a PDF. P1–P7 in plain-text and binary form, 16-bit depth and several images stored back to back in one file are supported; one image per page, stored losslessly, with optional A4 / Letter layout, all locally in your browser.

如何使用「PPM 转 PDF（支持 PGM / PBM / PAM）」？How do I use the PPM to PDF Converter tool?

在「PPM 转 PDF（支持 PGM / PBM / PAM）」中，选择或拖入文件，按需设置「页面大小」、「方向」、「页边距 (0–50 mm)」、「图片压缩」、「JPEG 质量 (30–100)」等选项，然后点击「生成 PDF」、「清空」按钮即可。In the PPM to PDF Converter: Choose or drop your files, set "Page size", "Orientation", "Margin (0–50 mm)", "Image compression", "JPEG quality (30–100)", then click "Create PDF", "Clear".

PPM、PGM、PBM、PAM 有什么区别？What's the difference between PPM, PGM, PBM and PAM?

它们都属于 Netpbm 家族：PBM 是黑白位图（P1 文本 / P4 二进制），PGM 是灰度图（P2 / P5），PPM 是 RGB 彩色图（P3 / P6），PAM（P7）是可带 Alpha 通道的通用格式。它们几乎不压缩、结构极简，常见于科研和图像处理程序的输出、OpenCV / ImageMagick 的中间文件和教学代码。They're all in the Netpbm family: PBM is black-and-white (P1 plain text / P4 binary), PGM greyscale (P2 / P5), PPM RGB colour (P3 / P6), and PAM (P7) a general format that can carry alpha. They're barely compressed and very simple, so they turn up as output from research and image-processing programs, as OpenCV / ImageMagick intermediates and in teaching code.

16 位和多图文件能转换吗？Can it convert 16-bit and multi-image files?

可以。最大值超过 255 的文件按 16 位（高字节在前）读取并换算到 8 位；二进制格式允许把多张图首尾相接存在一个文件里，这时每张图各占一页（最多 200 张），列表里会显示“文件内含 N 张图片”。注释行（# 开头）会被跳过。Yes. Files with a maxval above 255 are read as 16-bit (most significant byte first) and scaled to 8-bit. The binary formats allow several images back to back in one file; each then gets its own page (up to 200), and the list shows how many the file holds. Comment lines starting with # are skipped.

PDF 里的画质会变吗？Does quality change in the PDF?

默认无损：像素原样压缩写入 PDF，灰度和黑白图按灰度存储，体积通常比原始 PPM 小得多。也可以改用 JPEG 让照片类图片更小。By default it's lossless: the pixels are compressed into the PDF exactly, with greyscale and black-and-white images stored as greyscale, which is usually much smaller than the raw PPM. You can switch to JPEG to make photo-like images smaller.

页面大小和页边距怎么选？How do I choose page size and margins?

“按图片尺寸”让每页正好等于图片大小（按图片自带的 DPI 换算，没有 DPI 信息时按 96 DPI），页边距为 0 时没有白边（设置了页边距，四周会按该宽度留白）；选 A4 / Letter 等标准纸张时，图片会等比例缩放并居中，方向选“自动”时横图自动用横向页面。"Image size" makes each page exactly the size of its image (using the image's own DPI, or 96 DPI if none is stored), with no white border when the margin is 0 (a margin adds a white border of that width). With A4, Letter and other paper sizes the image is scaled proportionally and centred; with orientation on Auto, landscape images get landscape pages.

“无损”和“JPEG”有什么区别？What's the difference between Lossless and JPEG?

无损模式把像素原样压缩（类似 PNG，灰度图自动用灰度存储），画质完全不变，适合截图、文字扫描和线条图；JPEG 模式文件更小，适合照片。“自动”会按格式选择合适的方式。透明区域在无损模式下保留，JPEG 模式下填充白色。Lossless stores the pixels exactly (PNG-style compression; grayscale images are stored as grayscale), so quality is unchanged — best for screenshots, text scans and line art. JPEG gives smaller files and suits photos. Auto picks per format. Transparency is kept in Lossless mode and filled with white in JPEG mode.

图片会上传吗？Are my images uploaded?

不会。解码和生成 PDF 都在你的浏览器里完成（pdf-lib），图片不会离开你的设备。No. Decoding and PDF creation both happen in your browser (pdf-lib); your images never leave your device.

「PPM 转 PDF（支持 PGM / PBM / PAM）」免费吗？需要注册吗？Is the PPM to PDF Converter free? Do I need an account?

「PPM 转 PDF（支持 PGM / PBM / PAM）」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 PPM to PDF Converter is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.