在 IronOCR 中縮小 PDF 檔案大小

Curtis Chau

更新:2026年4月21日

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如何在 IronOCR 中縮小輸出 PDF 的檔案大小？

IronOCR 會自動將偵測到品質較低（低於 150 DPI）的輸入資料進行放大處理，以確保讀取結果的準確性。

若偵測到 DPI 低於 150，TargetDPI（預設值為 225 DPI）將定義 PDF 的渲染 DPI。這與手動設定 TargetDPI = 225 的效果相同。

為減小輸出檔案大小，您可以設定較低的 TargetDPI 值，這將產生更小的 PDF 檔案。然而，若設定過低可能會影響 OCR 效能，因此必須保持平衡。

建議數值為 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

Private 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 As 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

$vbLabelText $csharpLabel

若要停用自動放大功能，請使用 TargetDPI = 0。這將使 IronOCR 直接讀取輸入檔案，忽略 TargetDPI 的值。

更多資訊請參閱 API：IronOCR API 參考文件