Extract all images from a PDF in C#

Since 1.1View as Markdown

Save the images every page draws, as JPEG or PNG files.

Short answer

GetImages lists the images a page draws, with their placement and resolution. A JPEG (DCTDecode) is written as stored with GetEncodedData, so nothing is recompressed. Other images are decoded to 8 bit gray or RGB pixels with Decode and saved as PNG.

#:package PdfNetStack@1.2.0
using PdfNetStack;

PdfDocument doc = PdfDocument.Open("manual.pdf");
for (int p = 0; p < doc.Pages.Count; p++)
{
    IReadOnlyList<PdfPageImage> images = doc.Pages[p].GetImages();
    for (int i = 0; i < images.Count; i++)
    {
        PdfPageImage image = images[i];
        string name = $"page{p + 1}-image{i + 1}";
        if (image.Encoding == "DCTDecode")
        {
            File.WriteAllBytes(name + ".jpg", image.GetEncodedData());   // the JPEG as stored
        }
        else if (image.Decode() is PdfBitmap bitmap)
        {
            bitmap.SavePng(name + ".png");                                // 8 bit gray or RGB pixels
        }
        Console.WriteLine($"{name}: {image.Width}x{image.Height}, {image.Encoding ?? "raw"}, {image.HorizontalResolution:0} dpi");
    }
}

Notes

An image drawn on several pages is listed on each of them. HorizontalResolution and VerticalResolution give the dots per inch at which it is drawn.
Decode handles raw samples, JPEG, JPEG 2000, CCITT fax and JBIG2. Soft masks are not applied, and Decode returns null for an unsupported color space.