How to Manage DPI with IronPDF

Managing and Retrieving DPI with IronPDF

1. Setting DPI when Creating PDFs (HTML to PDF)

When rendering HTML to PDF, IronPDF defaults to standard screen resolution (typically 96 DPI). To increase the resolution for high-quality print outputs, you must define the DPI context when setting the paper size.

There is no standalone DPI property to set globally for the renderer; instead, you pass the desired DPI when defining the paper size in pixels or points.

Code Example:

using IronPdf;

var renderer = new ChromePdfRenderer();

// Set paper dimensions and force a specific DPI (e.g., 300 for print)

// Arguments: Width, Height, DPI

renderer.RenderingOptions.SetCustomPaperSizeinPixelsOrPoints(2480, 3508, 300);

var pdf = renderer.RenderHtmlAsPdf(“<h1>Print Ready Content</h1>”);

pdf.SaveAs(“high_quality.pdf”);

2. Managing DPI when Exporting PDFs (Rasterization)

When converting a PDF document into images (rasterization), DPI is a critical parameter that determines the pixel density and clarity of the output image.

• To Files: Use RasterizeToImageFiles with the DPI parameter.

• To Memory: Use ToBitmap or ToBitmapHighQuality.

Code Example:

using IronPdf;

var pdf = PdfDocument.FromFile(“input.pdf”);

// Rasterize to PNGs at 150 DPI (Balance between size and quality)

pdf.RasterizeToImageFiles(“page_*.png”, DPI: 150);

// Convert specific page to Bitmap in memory at 96 DPI (Standard screen)

var bitmap = pdf.ToBitmap(pageIndex: 0, DPI: 96);

3. Retrieving DPI from an Existing PDF

Can I get the DPI of a PDF Page?

No. It is not possible to “get” the DPI of a PDF page itself.

Why? PDF pages are vector-based documents defined by physical dimensions (Inches, Millimeters, or Points), not by pixel resolution.

• The native unit of a PDF is the Point.

• 1 Point = 1/72 of an inch.

• Because vectors (text and shapes) scale infinitely without losing quality, a PDF page does not have a native “resolution” or DPI until it is rasterized (converted to an image) or printed.

Can I get the DPI of Images inside a PDF?

Yes. While the page itself has no DPI, the raster images (photos, scans) embedded within the PDF do have a fixed resolution. You can extract these images to check their quality.

Code Example:

using IronPdf;

using IronSoftware.Drawing;

using System.Linq;

var pdf = PdfDocument.FromFile(“scanned_doc.pdf”);

// 1. Extract all images from the PDF

var images = pdf.ExtractAllBitmaps();

if (images.Any())

{

var firstImage = images.First();

// 2. Check the specific resolution of the embedded asset

// Returns resolution in pixels per inch

double dpiX = firstImage.HorizontalResolution;

double dpiY = firstImage.VerticalResolution;

}