Converting HTML to images is great for snapshots of dashboards, invoices, or receipts—but poor DPI, missing assets, or fragile CSS can ruin the result. This guide shows practical fixes for image quality and layout issues when using Aspose.HTML for .NET, plus a complete, compilable C# example.

Key Takeaways

  • Raise DPI with HorizontalResolution/VerticalResolution (96–150 for screens, 300 for print) and keep UseAntialiasing = true.
  • Resolve assets by loading with a base URI so relative CSS, images, and fonts work.
  • Pick the right CSS media: MediaType.Screen for on‑screen styles; MediaType.Print for @media print.
  • Control geometry via PageSetup.AnyPage (size + margins) to avoid clipping and forced line breaks.
  • Harden CSS: fixed table layout, collapsed borders, responsive images (max-width:100%; height:auto).

Common Problems & Fixes

1) Blurry or pixelated output

  • Increase DPI (HorizontalResolution/VerticalResolution).
  • Prefer PNG/WebP for UI/charts; avoid high JPEG compression on text.

2) Missing logos, CSS, or fonts

  • Use new HTMLDocument(pathOrHtml, baseUri) so relative URLs resolve.
  • Ensure fonts are accessible (embed via @font-face or install on server).

3) Broken tables or overflow

  • Add CSS: table{table-layout:fixed} and th,td{word-wrap:break-word}.
  • Consider a wider page size or smaller margins.

4) Wrong styles applied

  • Toggle options.Css.MediaType between Screen and Print to match intended rules.

Complete Example (Compilable C#)

using System;
using System.IO;
using Aspose.Html;
using Aspose.Html.Converters;
using Aspose.Html.Saving;            // ImageSaveOptions
using Aspose.Html.Rendering;         // MediaType
using Aspose.Html.Rendering.Image;   // ImageFormat
using Aspose.Html.Drawing;           // Length, Size, Margin, Page

namespace HtmlToImageTroubleshooting
{
    internal static class Program
    {
        // How to run:
        // 1) dotnet new console -n HtmlToImageTroubleshooting
        // 2) cd HtmlToImageTroubleshooting
        // 3) dotnet add package Aspose.HTML
        // 4) Replace Program.cs with this file's contents
        // 5) dotnet run -- "path-to-input.html"   (argument optional)
        private static void Main(string[] args)
        {
            string outDir = Path.Combine(Directory.GetCurrentDirectory(), "out");
            Directory.CreateDirectory(outDir);

            // Load HTML from file if provided; otherwise use inline HTML with resilient defaults
            HTMLDocument document;
            if (args.Length > 0 && File.Exists(args[0]))
            {
                // Use path as both content and base URI so relative links resolve
                string path = Path.GetFullPath(args[0]);
                string baseDir = Path.GetDirectoryName(path) ?? ".";
                document = new HTMLDocument(path, baseDir);
            }
            else
            {
                string html = "<!DOCTYPE html>" +
                              "<html><head><meta charset=\\\"utf-8\\\"><title>HTML→Image Troubleshooting</title>" +
                              // Hardened CSS: responsive images, fixed tables, clear borders
                              "<style>html,body{margin:0;padding:0;font-family:Arial,Helvetica,sans-serif;color:#222}" +
                              "img{max-width:100%;height:auto;display:block}" +
                              "table{width:100%;border-collapse:collapse;table-layout:fixed}" +
                              "th,td{border:1px solid #ddd;padding:6px 8px;vertical-align:top;word-wrap:break-word}" +
                              "h1{margin:12px 0}" +
                              "@media print{body{font-size:12pt}}" +
                              "</style></head><body>" +
                              "<h1>Invoice #1001</h1>" +
                              "<img src=\\\"./assets/logo.png\\\" alt=\\\"Company logo\\\" style=\\\"width:220px\\\">" +
                              "<table><tr><th>Item</th><th>Qty</th><th>Price</th></tr>" +
                              "<tr><td>Widget A very long text that wraps as needed</td><td>5</td><td>$12.00</td></tr>" +
                              "<tr><td>Widget B</td><td>2</td><td>$9.50</td></tr></table>" +
                              "</body></html>";
                document = new HTMLDocument(html, ".");
            }

            using (document)
            {
                var mm = Length.FromMillimeters;

                // High-quality PNG at 300 DPI (Screen CSS)
                var png = new ImageSaveOptions(ImageFormat.Png)
                {
                    UseAntialiasing = true
                };
                png.HorizontalResolution = 300;
                png.VerticalResolution   = 300;
                png.Css.MediaType        = MediaType.Screen; // Use Print for @media print
                png.PageSetup.AnyPage    = new Page(
                    new Size(mm(210), mm(297)), // A4
                    new Margin(mm(10), mm(10), mm(10), mm(10))
                );

                string pngPath = Path.Combine(outDir, "render-300dpi.png");
                Converter.ConvertHTML(document, png, pngPath);
                Console.WriteLine($"Saved: {pngPath}");

                // Smaller JPEG at 150 DPI (Print CSS) for lightweight previews
                var jpg = new ImageSaveOptions(ImageFormat.Jpeg);
                jpg.HorizontalResolution = 150;
                jpg.VerticalResolution   = 150;
                jpg.Css.MediaType        = MediaType.Print;
                jpg.PageSetup.AnyPage    = png.PageSetup.AnyPage; // reuse geometry

                string jpgPath = Path.Combine(outDir, "render-150dpi.jpg");
                Converter.ConvertHTML(document, jpg, jpgPath);
                Console.WriteLine($"Saved: {jpgPath}");
            }
        }
    }
}

Step‑by‑Step Troubleshooting

A) Identify the issue

Is it blurry output, missing assets, wrong styles, or layout overflow? Reproduce with a small sample HTML first.

B) Validate and simplify HTML

Run your HTML through a validator; remove dead CSS/JS and heavy effects that don’t affect the snapshot.

C) Configure Aspose.HTML

  • Pick target DPI and format (PNG/JPEG/WebP/TIFF).
  • Set page size/margins to match content.
  • Choose Screen or Print media.

D) Harden CSS for raster output

  • Responsive images and fixed table layout;
  • Collapse borders and enable word‑wrap on th, td.

E) Verify fonts and assets

  • Ensure fonts, images, and CSS are reachable from the base URI.

FAQ

Q1. My output is blurry—what should I change first? Increase DPI to 300 and keep UseAntialiasing = true. Prefer PNG/WebP for text‑heavy UIs.

Q2. Why are images or styles missing in the output? Your relative URLs likely don’t resolve. Load with a base URI that points to the folder containing CSS/images/fonts.

Q3. The output ignores my print styles—how do I apply them? Set options.Css.MediaType = MediaType.Print so @media print rules apply.

Q4. Tables overflow the page—how can I fix this? Use table-layout:fixed, collapsed borders, word-wrap:break-word, and widen the page or reduce margins.

Q5. Can I export to WebP or TIFF? Yes, via new ImageSaveOptions(ImageFormat.Webp) or ImageFormat.Tiff depending on delivery and archival needs.

How to Run HTML to Image

  1. Create a console app:

    dotnet new console -n HtmlToImageTroubleshooting
cd HtmlToImageTroubleshooting

  2. Add the package:

    dotnet add package Aspose.HTML

  3. Replace Program.cs with the Complete Example above.

  4. Run with an HTML file (optional):

    dotnet run -- ../path/to/sample.html

Conclusion

By combining a base URI, right media, robust CSS, and tuned DPI/page geometry, you’ll get sharp, predictable HTML→image outputs with Aspose.HTML for .NET—even on complex layouts.

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