在 IronOCR 中减少 PDF 文件大小

Curtis Chau

Updated: 2026年6月29日

如何减小 IronOCR 输出 PDF 的文件大小？

IronOCR 会自动将检测到的低质量（低于 150DPI）的输入图像放大，以确保准确的读取结果。

如果检测到 DPI 低于 150，则 TargetDPI（默认 225DPI）定义 PDF 渲染的 DPI。这等同于手动设置TargetDPI = 225。

为了减小输出文件的大小，您可以设置一个较低的TargetDPI，这将创建较小的PDF。但是，设置得太低可能会影响 OCR 性能，因此保持平衡至关重要。

建议值分别为 96、72、48。

// Example of reducing PDF output file size by lowering the DPI

// Example 1: Reducing DPI to 96
using IronOcr;  // Import IronOCR namespace

var Ocr = new IronTesseract(); // Initialize IronTesseract for OCR operations

using (var Input = new OcrInput()) // Create OCR input object
{
    Input.TargetDPI = 96;    // Set the desired DPI; 96 is used for smaller output size
    Input.AddPdf("example.pdf", "password"); // Add input PDF (with optional password)
    
    var Result = Ocr.Read(Input); // Perform OCR on the input
    Console.WriteLine(Result.Text); // Output recognized text to the console
}

// Example 2: Another way to set DPI
var ocr = new IronTesseract();

using (var ocrInput = new OcrInput()) // Create a new OCR input object
{
    ocrInput.AddPdf("img/Input.pdf", 72); // Add PDF with the specified DPI of 72
    var ocrResult = ocr.Read(ocrInput); // Read and process the PDF

    ocrResult.SaveAsSearchablePdf(@"Output.pdf"); // Save result to a searchable PDF
}

// Example of reducing PDF output file size by lowering the DPI

// Example 1: Reducing DPI to 96
using IronOcr;  // Import IronOCR namespace

var Ocr = new IronTesseract(); // Initialize IronTesseract for OCR operations

using (var Input = new OcrInput()) // Create OCR input object
{
    Input.TargetDPI = 96;    // Set the desired DPI; 96 is used for smaller output size
    Input.AddPdf("example.pdf", "password"); // Add input PDF (with optional password)
    
    var Result = Ocr.Read(Input); // Perform OCR on the input
    Console.WriteLine(Result.Text); // Output recognized text to the console
}

// Example 2: Another way to set DPI
var ocr = new IronTesseract();

using (var ocrInput = new OcrInput()) // Create a new OCR input object
{
    ocrInput.AddPdf("img/Input.pdf", 72); // Add PDF with the specified DPI of 72
    var ocrResult = ocr.Read(ocrInput); // Read and process the PDF

    ocrResult.SaveAsSearchablePdf(@"Output.pdf"); // Save result to a searchable PDF
}

' Example of reducing PDF output file size by lowering the DPI

' Example 1: Reducing DPI to 96
Imports IronOcr  ' Import IronOCR namespace

Dim Ocr = New IronTesseract() ' Initialize IronTesseract for OCR operations

Using Input = New OcrInput() ' Create OCR input object
    Input.TargetDPI = 96    ' Set the desired DPI; 96 is used for smaller output size
    Input.AddPdf("example.pdf", "password") ' Add input PDF (with optional password)
    
    Dim Result = Ocr.Read(Input) ' Perform OCR on the input
    Console.WriteLine(Result.Text) ' Output recognized text to the console
End Using

' Example 2: Another way to set DPI
Dim ocr = New IronTesseract()

Using ocrInput = New OcrInput() ' Create a new OCR input object
    ocrInput.AddPdf("img/Input.pdf", 72) ' Add PDF with the specified DPI of 72
    Dim ocrResult = ocr.Read(ocrInput) ' Read and process the PDF

    ocrResult.SaveAsSearchablePdf("Output.pdf") ' Save result to a searchable PDF
End Using

' Example of reducing PDF output file size by lowering the DPI

' Example 1: Reducing DPI to 96
Imports IronOcr  ' Import IronOCR namespace

Dim Ocr = New IronTesseract() ' Initialize IronTesseract for OCR operations

Using Input = New OcrInput() ' Create OCR input object
    Input.TargetDPI = 96    ' Set the desired DPI; 96 is used for smaller output size
    Input.AddPdf("example.pdf", "password") ' Add input PDF (with optional password)
    
    Dim Result = Ocr.Read(Input) ' Perform OCR on the input
    Console.WriteLine(Result.Text) ' Output recognized text to the console
End Using

' Example 2: Another way to set DPI
Dim ocr = New IronTesseract()

Using ocrInput = New OcrInput() ' Create a new OCR input object
    ocrInput.AddPdf("img/Input.pdf", 72) ' Add PDF with the specified DPI of 72
    Dim ocrResult = ocr.Read(ocrInput) ' Read and process the PDF

    ocrResult.SaveAsSearchablePdf("Output.pdf") ' Save result to a searchable PDF
End Using

要禁用自动放大，请使用TargetDPI = 0。这将使 IronOCR 按原样读取输入文件，忽略 TargetDPI 值。

更多信息请参阅 API： IronOCR API 参考