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PDF Oxide

图片操作

PDF Oxide 提供两个级别的图片操作：通过 DocumentEditor 的底层操作（按 XObject 名称重新定位和调整图片大小），以及通过 PdfPage 的 DOM 级别访问（查询图片元数据）。两种方式都适用于已嵌入 PDF 中的图片。

获取页面图片

DocumentEditor：底层图片信息

获取页面上所有图片的详细放置信息，包括 XObject 名称和变换矩阵。

from pdf_oxide import PdfDocument

doc = PdfDocument("brochure.pdf")
images = doc.page_images(0)

for img in images:
    print(f"Name: {img['name']}")
    print(f"Position: ({img['x']:.1f}, {img['y']:.1f})")
    print(f"Size: {img['width']:.1f} x {img['height']:.1f}")
    print(f"Matrix: {img['matrix']}")

import { WasmPdfDocument } from "pdf-oxide-wasm";

const doc = new WasmPdfDocument(bytes);
const images = doc.pageImages(0);

for (const img of images) {
  console.log(`Name: ${img.name}`);
  console.log(`Position: (${img.x}, ${img.y})`);
  console.log(`Size: ${img.width} x ${img.height}`);
}
doc.free();

use pdf_oxide::editor::DocumentEditor;

let mut editor = DocumentEditor::open("brochure.pdf")?;
let images = editor.get_page_images(0)?;

for img in &images {
    println!("Name: {}", img.name);
    println!("Bounds: {:?}", img.bounds);  // [x, y, width, height]
    println!("Matrix: {:?}", img.matrix);  // [a, b, c, d, e, f]
}

返回的 ImageInfo 结构体包含：

字段 类型 描述
name String XObject 名称 (e.g., "Im0", "Image1")
bounds [f32; 4] Position and size [x, y, width, height]
matrix [f32; 6] Full transformation matrix [a, b, c, d, e, f]

PdfPage：DOM 级别图片信息

DOM API 提供每张图片更丰富的元数据。

doc = PdfDocument("brochure.pdf")
page = doc.page(0)

for img in page.find_images():
    print(f"BBox: {img.bbox}")
    print(f"Format: {img.format}")
    print(f"Dimensions: {img.dimensions}")

let mut doc = Pdf::open("brochure.pdf")?;
let page = doc.page(0)?;

for img in page.find_images() {
    println!("BBox: {:?}", img.bbox());
    println!("Format: {:?}", img.format());
    println!("Dimensions: {:?}", img.dimensions());
    println!("Aspect ratio: {:.2}", img.aspect_ratio());
    println!("Grayscale: {}", img.is_grayscale());

    if let Some(alt) = img.alt_text() {
        println!("Alt text: {}", alt);
    }
    if let Some((h_dpi, v_dpi)) = img.resolution() {
        println!("Resolution: {:.0} x {:.0} DPI", h_dpi, v_dpi);
    }
}

重新定位图片

将图片移动到页面上的新位置而不改变其大小。

doc = PdfDocument("input.pdf")
images = doc.page_images(0)

# Move the first image to position (100, 500)
doc.reposition_image(0, images[0]["name"], 100, 500)
doc.save("moved.pdf")

import { WasmPdfDocument } from "pdf-oxide-wasm";

const doc = new WasmPdfDocument(bytes);
const images = doc.pageImages(0);

// Move the first image to position (100, 500)
doc.repositionImage(0, images[0].name, 100, 500);
const output = doc.save();
doc.free();

let mut editor = DocumentEditor::open("input.pdf")?;
let images = editor.get_page_images(0)?;

// Move the first image
editor.reposition_image(0, &images[0].name, 100.0, 500.0)?;
editor.save("moved.pdf")?;

调整图片大小

改变图片的尺寸而不移动其位置。

doc = PdfDocument("input.pdf")
images = doc.page_images(0)

# Resize the first image to 300x200 points
doc.resize_image(0, images[0]["name"], 300, 200)
doc.save("resized.pdf")

import { WasmPdfDocument } from "pdf-oxide-wasm";

const doc = new WasmPdfDocument(bytes);
const images = doc.pageImages(0);

// Resize the first image to 300x200 points
doc.resizeImage(0, images[0].name, 300, 200);
const output = doc.save();
doc.free();

let mut editor = DocumentEditor::open("input.pdf")?;
let images = editor.get_page_images(0)?;

editor.resize_image(0, &images[0].name, 300.0, 200.0)?;
editor.save("resized.pdf")?;

设置完整图片边界

在一次操作中同时设置位置和大小。

doc = PdfDocument("input.pdf")
images = doc.page_images(0)

# Set position (72, 600) and size (468, 200)
doc.set_image_bounds(0, images[0]["name"], 72, 600, 468, 200)
doc.save("adjusted.pdf")

let mut editor = DocumentEditor::open("input.pdf")?;
let images = editor.get_page_images(0)?;

// x, y, width, height
editor.set_image_bounds(0, &images[0].name, 72.0, 600.0, 468.0, 200.0)?;
editor.save("adjusted.pdf")?;

管理图片修改

清除修改

在保存之前丢弃页面上所有待处理的图片修改。

doc.clear_image_modifications(0)

editor.clear_image_modifications(0);

检查待处理的修改

if doc.has_image_modifications(0):
    print("Page 0 has pending image changes")

if editor.has_image_modifications(0) {
    println!("Page 0 has pending image changes");
}

PdfImage DOM API（Rust）

DOM 级别的 PdfImage 为页面上找到的每张图片提供丰富的元数据。

方法 返回值 描述
id() ElementId 唯一元素标识符
bbox() Rect 页面上的位置和大小
format() ImageFormat 图像格式 (JPEG, PNG, etc.)
dimensions() (u32, u32) 宽度和高度（像素）
aspect_ratio() f32 宽高比
is_grayscale() bool 如果是灰度图片则为 true
alt_text() Option<&str> 无障碍替代文本
set_alt_text(text) () 设置无障碍替代文本
resolution() Option<(f32, f32)> DPI，格式为（水平，垂直）
horizontal_dpi() Option<f32> 水平 DPI
vertical_dpi() Option<f32> 垂直 DPI
is_high_resolution() bool 分辨率 >= 300 DPI
is_medium_resolution() bool 分辨率在 150-300 DPI 之间
is_low_resolution() bool 分辨率 < 150 DPI

在区域中查找图片

use pdf_oxide::geometry::Rect;

let page = doc.page(0)?;

// Find images in the top half of the page
let region = Rect::new(0.0, 396.0, 612.0, 396.0);
let top_images = page.find_images_in_region(region);
println!("Found {} images in top half", top_images.len());

设置无障碍替代文本

let mut page = doc.page(0)?;
let images = page.find_images();

for img in &images {
    if img.alt_text().is_none() {
        page.set_image_alt_text(img.id(), "Descriptive alt text")?;
    }
}

doc.save_page(page)?;

完整 API 参考

DocumentEditor 图片方法

方法 返回值 描述
get_page_images(page) Result<Vec<ImageInfo>> 列出页面上的所有图片
reposition_image(page, name, x, y) Result<()> 移动图片到新位置
resize_image(page, name, w, h) Result<()> 更改图片尺寸
set_image_bounds(page, name, x, y, w, h) Result<()> 设置位置和大小
clear_image_modifications(page) () 丢弃待处理的更改
has_image_modifications(page) bool 检查待处理的更改

高级示例：居中所有图片

use pdf_oxide::editor::DocumentEditor;

let mut editor = DocumentEditor::open("input.pdf")?;
let count = editor.current_page_count();

for page_idx in 0..count {
    let media_box = editor.get_page_media_box(page_idx)?;
    let page_width = media_box[2] - media_box[0];

    let images = editor.get_page_images(page_idx)?;
    for img in &images {
        let img_width = img.bounds[2];
        let centered_x = (page_width - img_width) / 2.0;

        editor.reposition_image(page_idx, &img.name, centered_x, img.bounds[1])?;
    }
}

editor.save("centered.pdf")?;

高级示例：缩放至适配宽度

from pdf_oxide import PdfDocument

doc = PdfDocument("photos.pdf")

for page_idx in range(doc.page_count()):
    media_box = doc.page_media_box(page_idx)
    page_width = media_box[2] - media_box[0]
    margin = 72  # 1 inch

    images = doc.page_images(page_idx)
    for img in images:
        target_width = page_width - 2 * margin
        scale = target_width / img["width"]
        new_height = img["height"] * scale

        doc.set_image_bounds(
            page_idx, img["name"],
            margin, img["y"],
            target_width, new_height
        )

doc.save("fitted.pdf")

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