在IronOCR中減少PDF文件大小

Curtis Chau

Updated: 2026年6月29日

如何在IronOCR中減少輸出PDF的文件大小？

IronOCR會自動將檢測為低質量（低於150DPI）的輸入進行放大，以確保準確的讀取結果。

如果檢測到DPI低於150，TargetDPI（預設為225DPI）界定了PDF渲染的DPI。這與手動設置TargetDPI = 225相同。

要減少輸出文件大小，您可以設置較低的TargetDPI，這將建立較小的PDF。然而，設置得過低可能會影響OCR性能，因此保持平衡至關重要。

建議的值有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

要禁用自動放大功能，請使用TargetDPI = 0。這將使IronOCR按原樣讀取輸入文件，忽略TargetDPI值。

有關更多資訊，請參閱API：IronOCR API Reference