在 IronOCR 中減少 PDF 檔案大小

Curtis Chau

更新:6月 1, 2025

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如何減少 IronOCR 輸出 PDF 的檔案大小？

IronOCR 會自動將偵測到的低品質（低於 150DPI）的輸入影像放大，以確保準確的讀取結果。

如果偵測到 DPI 低於 150，則 TargetDPI（預設為 225DPI）定義 PDF 渲染的 DPI。這與手動設定TargetDPI = 225效果相同。

為了減少輸出檔案大小，您可以設定較低的TargetDPI ，這樣就能建立更小的 PDF 檔案。但是，設定得太低可能會影響 OCR 效能，因此保持平衡至關重要。

建議值分別為 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

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若要停用自動放大，請使用TargetDPI = 0 。這將使 IronOCR 以原樣讀取輸入文件，忽略 TargetDPI 值。

更多資訊請參閱 API： IronOCR API 參考