以编程方式裁剪 PDF 页面 C#

获取页面属性

每个 PDF 文件中的页面都有多个属性，例如宽度、高度、出血框、裁剪框和修整框。Aspose.PDF 允许您访问这些属性。

• 媒体框：媒体框是最大的页面框。它对应于在将文档打印为 PostScript 或 PDF 时选择的页面大小（例如 A4、A5、美国信纸等）。换句话说，媒体框决定了 PDF 文档显示或打印的介质的物理大小。
• 出血框：如果文档有出血，PDF 也将有一个出血框。出血是指超出页面边缘的颜色（或艺术作品）量。它用于确保在文档打印并裁剪到大小（“修整”）时，墨水会延伸到页面的边缘。即使页面被错误裁剪 - 稍微偏离修整标记 - 页面上也不会出现白边。
• 修整框：修整框指的是文档在打印和修整后最终的大小。
• 艺术框：艺术框是绘制在文档页面实际内容周围的框。此页面框在将 PDF 文档导入其他应用程序时使用。
• 裁剪框：裁剪框是您的 PDF 文档在 Adobe Acrobat 中显示的“页面”大小。在正常视图中，只有裁剪框的内容在 Adobe Acrobat 中显示。有关这些属性的详细描述，请阅读 Adobe.Pdf 规范，特别是 10.10.1 页面边界。
• Page.Rect：媒体框和裁剪框的交集（通常可见的矩形）。下图说明了这些属性。 有关更多详细信息，请访问 此页面。

以下代码片段也适用于 Aspose.PDF.Drawing 库。

下面的代码片段展示了如何裁剪页面：

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void CropPage()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Pages();

    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "CropPageInput.pdf"))
    {
        Console.WriteLine(document.Pages[1].CropBox);
        Console.WriteLine(document.Pages[1].TrimBox);
        Console.WriteLine(document.Pages[1].ArtBox);
        Console.WriteLine(document.Pages[1].BleedBox);
        Console.WriteLine(document.Pages[1].MediaBox);
        // Create new Box rectangle
        var newBox = new Rectangle(200, 220, 2170, 1520);
        document.Pages[1].CropBox = newBox;
        document.Pages[1].TrimBox = newBox;
        document.Pages[1].ArtBox = newBox;
        document.Pages[1].BleedBox = newBox;
        // Save PDF document
        document.Save(dataDir + "CropPage_out.pdf");  
    }
}

在此示例中，我们使用了一个示例文件 这里。最初我们的页面看起来如图 1 所示。

更改后，页面将看起来像图 2。

修整页面周围的白边

例如，您可以使用任何可以加载位图的图形库修整页面周围的白边：

.NET Core 3.1

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void TrimWhiteSpaceAroundPage()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Pages();
    
    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "TrimWhiteSpaceAroundPage.pdf"))
    {
        var device = new Aspose.Pdf.Devices.PngDevice(new Aspose.Pdf.Devices.Resolution(300));

        using (var imageStr = new MemoryStream())
        {
            // Convert page to PNG image
            device.Process(document.Pages[1], imageStr);
            using (var pageBitmap = new Bitmap(imageStr))
            {
                document.Pages[1].CropBox = GetNewCropBox(pageBitmap, document.Pages[1].CropBox);
            }
        }
        // Save PDF document
        document.Save(dataDir + "TrimWhiteSpaceAroundPage_out.pdf");
    }
}

// Determine white areas with System.Drawing
private static Aspose.Pdf.Rectangle GetNewCropBox(Bitmap pageBitmap, Aspose.Pdf.Rectangle prevCropBox)
{
    var imageBitmapData = pageBitmap.LockBits(new Rectangle(0, 0, pageBitmap.Width, pageBitmap.Height),
                            ImageLockMode.ReadOnly, PixelFormat.Format32bppRgb);

    int toHeight = pageBitmap.Height;
    int toWidth = pageBitmap.Width;

    int? leftNonWhite = null;
    int? rightNonWhite = null;
    int? topNonWhite = null;
    int? bottomNonWhite = null;

    var imageRowBytes = new byte[imageBitmapData.Stride];
    for (int y = 0; y < toHeight; y++)
    {
        // Copy the row data to byte array
        if (IntPtr.Size == 4)
        {
            Marshal.Copy(new IntPtr(imageBitmapData.Scan0.ToInt32() + y * imageBitmapData.Stride), imageRowBytes, 0, imageBitmapData.Stride);
        }
        else
        {
            Marshal.Copy(new IntPtr(imageBitmapData.Scan0.ToInt64() + y * imageBitmapData.Stride), imageRowBytes, 0, imageBitmapData.Stride);
        }

        int? leftNonWhite_row = null;
        int? rightNonWhite_row = null;

        for (int x = 0; x < toWidth; x++)
        {
            if (imageRowBytes[x * 4] != 255
                || imageRowBytes[x * 4 + 1] != 255
                || imageRowBytes[x * 4 + 2] != 255)
            {
                if (leftNonWhite_row == null)
                {
                    leftNonWhite_row = x;
                }

                rightNonWhite_row = x;
            }
        }

        if (leftNonWhite_row != null || rightNonWhite_row != null)
        {
            if (topNonWhite == null)
            {
                topNonWhite = y;
            }

            bottomNonWhite = y;
        }

        if (leftNonWhite_row != null
            && (leftNonWhite == null || leftNonWhite > leftNonWhite_row))
        {
            leftNonWhite = leftNonWhite_row;
        }
        if (rightNonWhite_row != null
            && (rightNonWhite == null || rightNonWhite < rightNonWhite_row))
        {
            rightNonWhite = rightNonWhite_row;
        }
    }

    leftNonWhite = leftNonWhite ?? 0;
    rightNonWhite = rightNonWhite ?? toWidth;
    topNonWhite = topNonWhite ?? 0;
    bottomNonWhite = bottomNonWhite ?? toHeight;

    double xCoef = prevCropBox.Width / toWidth;
    double yCoef = prevCropBox.Height / toHeight;

    pageBitmap.UnlockBits(imageBitmapData);
    
    // Create crop box with correction to previous crop box
    return
        new Aspose.Pdf.Rectangle(
            leftNonWhite.Value * xCoef + prevCropBox.LLX,
            (toHeight * yCoef + prevCropBox.LLY) - bottomNonWhite.Value * yCoef,
            rightNonWhite.Value * xCoef + prevCropBox.LLX,
            (toHeight * yCoef + prevCropBox.LLY) - topNonWhite.Value * yCoef
        );
}

.NET 8

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void TrimWhiteSpaceAroundPage()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Pages();

    // Open PDF document
    using var document = new Aspose.Pdf.Document(dataDir + "TrimWhiteSpaceAroundPage.pdf");
    var device = new Aspose.Pdf.Devices.PngDevice(new Aspose.Pdf.Devices.Resolution(300));

    using var imageStr = new MemoryStream();

    // Convert page to PNG image
    device.Process(document.Pages[1], imageStr);
    using var pageBitmap = new Bitmap(imageStr);
    document.Pages[1].CropBox = GetNewCropBox(pageBitmap, document.Pages[1].CropBox);

    // Save PDF document
    document.Save(dataDir + "TrimWhiteSpaceAroundPage_out.pdf");
}

// Determine white areas with System.Drawing
private static Aspose.Pdf.Rectangle GetNewCropBox(Bitmap pageBitmap, Aspose.Pdf.Rectangle prevCropBox)
{
    var imageBitmapData = pageBitmap.LockBits(new Rectangle(0, 0, pageBitmap.Width, pageBitmap.Height),
                            ImageLockMode.ReadOnly, PixelFormat.Format32bppRgb);

    int toHeight = pageBitmap.Height;
    int toWidth = pageBitmap.Width;

    int? leftNonWhite = null;
    int? rightNonWhite = null;
    int? topNonWhite = null;
    int? bottomNonWhite = null;

    var imageRowBytes = new byte[imageBitmapData.Stride];
    for (int y = 0; y < toHeight; y++)
    {
        // Copy the row data to byte array
        if (IntPtr.Size == 4)
        {
            Marshal.Copy(new IntPtr(imageBitmapData.Scan0.ToInt32() + y * imageBitmapData.Stride), imageRowBytes, 0, imageBitmapData.Stride);
        }
        else
        {
            Marshal.Copy(new IntPtr(imageBitmapData.Scan0.ToInt64() + y * imageBitmapData.Stride), imageRowBytes, 0, imageBitmapData.Stride);
        }

        int? leftNonWhite_row = null;
        int? rightNonWhite_row = null;

        for (int x = 0; x < toWidth; x++)
        {
            if (imageRowBytes[x * 4] != 255
                || imageRowBytes[x * 4 + 1] != 255
                || imageRowBytes[x * 4 + 2] != 255)
            {
                if (leftNonWhite_row == null)
                {
                    leftNonWhite_row = x;
                }

                rightNonWhite_row = x;
            }
        }

        if (leftNonWhite_row != null || rightNonWhite_row != null)
        {
            if (topNonWhite == null)
            {
                topNonWhite = y;
            }

            bottomNonWhite = y;
        }

        if (leftNonWhite_row != null
            && (leftNonWhite == null || leftNonWhite > leftNonWhite_row))
        {
            leftNonWhite = leftNonWhite_row;
        }
        if (rightNonWhite_row != null
            && (rightNonWhite == null || rightNonWhite < rightNonWhite_row))
        {
            rightNonWhite = rightNonWhite_row;
        }
    }

    leftNonWhite = leftNonWhite ?? 0;
    rightNonWhite = rightNonWhite ?? toWidth;
    topNonWhite = topNonWhite ?? 0;
    bottomNonWhite = bottomNonWhite ?? toHeight;

    double xCoef = prevCropBox.Width / toWidth;
    double yCoef = prevCropBox.Height / toHeight;

    pageBitmap.UnlockBits(imageBitmapData);
    
    // Create crop box with correction to previous crop box
    return
        new Aspose.Pdf.Rectangle(
            leftNonWhite.Value * xCoef + prevCropBox.LLX,
            (toHeight * yCoef + prevCropBox.LLY) - bottomNonWhite.Value * yCoef,
            rightNonWhite.Value * xCoef + prevCropBox.LLX,
            (toHeight * yCoef + prevCropBox.LLY) - topNonWhite.Value * yCoef
        );
}