ImageResizer.AspNetCore (Core5.ImageResizer)

A lightweight, fast image processing middleware for ASP.NET Core that enables on-the-fly image resizing, cropping, format conversion, and watermarking through simple URL query parameters.

Note: This is a maintained fork of ImageResizer.AspNetCore updated to support newer .NET versions (.NET 5.0+, including .NET 9.0 and .NET 10.0).

Features

• Resize images - Scale images to specific dimensions
• Crop images - Extract specific regions from images
• Format conversion - Convert between PNG, JPG, and JPEG
• Image quality control - Adjust compression quality
• Auto-rotation - Automatically rotate images based on EXIF orientation
• Padding mode - Add padding to maintain aspect ratio
• Max mode - Scale to fit within bounds while maintaining aspect ratio
• Crop mode - Crop to exact dimensions
• Stretch mode - Stretch image to exact dimensions
• Watermarking - Add text or image watermarks
• Memory caching - Automatically cache processed images
• Multi-framework support - Supports .NET 5.0+

Installation

Install via NuGet:

dotnet add package Core5.ImageResizer

Or using Package Manager Console:

Install-Package Core5.ImageResizer

Quick Start

1. Register the Service

In your Program.cs (ASP.NET Core 6+):

using ImageResizer.AspNetCore;

var builder = WebApplication.CreateBuilder(args);

// Add ImageResizer service
builder.Services.AddImageResizer();

var app = builder.Build();

// Use ImageResizer middleware
app.UseStaticFiles();
app.UseImageResizer();

app.Run();

Or in Startup.cs (ASP.NET Core 5):

public void ConfigureServices(IServiceCollection services)
{
    services.AddImageResizer();
}

public void Configure(IApplicationBuilder app)
{
    app.UseStaticFiles();
    app.UseImageResizer();
}

2. Use in HTML

Simply add query parameters to your image URLs:

<img src="~/images/photo.jpg?w=200" alt="Resized" />
<img src="~/images/photo.jpg?w=200&h=300" alt="Resized with height" />

Usage Examples

Basic Resizing

Resize to a specific width (height auto-calculated to maintain aspect ratio):

<img src="~/images/photo.jpg?w=300" alt="Width 300px" />

Resize to a specific height (width auto-calculated):

<img src="~/images/photo.jpg?h=400" alt="Height 400px" />

Resize to specific width and height with auto-detection of best fit:

<img src="~/images/photo.jpg?w=200&h=200" alt="Max fit" />

Format Conversion

Convert to PNG:

<img src="~/images/photo.jpg?format=png" alt="PNG format" />

Convert to JPEG with quality setting:

<img src="~/images/photo.png?format=jpg&quality=80" alt="JPEG format" />

Resize Modes

Max mode (default) - Fit within bounds maintaining aspect ratio:

<img src="~/images/photo.jpg?w=200&h=200&mode=max" alt="Max fit" />

Pad mode - Fit within bounds and pad with white space:

<img src="~/images/photo.jpg?w=200&h=200&mode=pad" alt="Padded" />

Crop mode - Crop to exact dimensions from center:

<img src="~/images/photo.jpg?w=200&h=200&mode=crop" alt="Cropped" />

Stretch mode - Stretch to exact dimensions (may distort):

<img src="~/images/photo.jpg?w=200&h=200&mode=stretch" alt="Stretched" />

Quality Control

Adjust compression quality (1-100, default 100):

<img src="~/images/photo.jpg?w=800&quality=75" alt="Optimized" />

Auto-Rotation

Enable automatic EXIF-based rotation:

<img src="~/images/photo.jpg?autorotate=true" alt="Auto-rotated" />

Combined Parameters

Use multiple parameters together:

<!-- Resize to 500x300, crop to fill, JPEG format, 80% quality -->
<img src="~/images/photo.jpg?w=500&h=300&mode=crop&format=jpg&quality=80" alt="Optimized" />

<!-- Resize width to 400, auto-height, PNG format, auto-rotate -->
<img src="~/images/photo.jpg?w=400&format=png&autorotate=true" alt="Responsive" />

Watermarking

Add text watermark (requires ImageResizerJson.json configuration):

<img src="~/images/photo.jpg?w=400&wmtext=1" alt="With watermark" />

Add image watermark:

<img src="~/images/photo.jpg?w=400&wmimage=1" alt="With image watermark" />

Query Parameters Reference

Parameter	Type	Default	Description
w	int	0	Width in pixels (0 = auto-calculate)
h	int	0	Height in pixels (0 = auto-calculate)
mode	string	max	Resize mode: max, pad, crop, stretch
format	string	original	Output format: jpg, jpeg, png
quality	int	100	JPEG quality (1-100)
autorotate	bool	false	Auto-rotate based on EXIF orientation
wmtext	int	0	Text watermark ID (requires config)
wmimage	int	0	Image watermark ID (requires config)

Watermark Configuration

To use watermarks, create an ImageResizerJson.json file in your wwwroot directory:

{
  "WatermarkTextList": [
    {
      "Key": 1,
      "Text": "© 2024 MyCompany",
      "Color": "#FFFFFF",
      "Size": 30,
      "Opacity": 0.7
    }
  ],
  "WatermarkImageList": [
    {
      "Key": 1,
      "ImagePath": "/images/watermark.png",
      "Opacity": 0.5
    }
  ]
}

Performance

• Memory caching - Processed images are automatically cached in memory
• Fast processing - Uses SkiaSharp for efficient image manipulation
• Responsive - Query parameters are parsed only when needed
• Lightweight - Minimal dependencies

Supported Image Formats

• Input: PNG, JPG, JPEG
• Output: PNG, JPG, JPEG

Browser Compatibility

Works with all modern browsers that support standard image tags. The resizing happens server-side, so all clients can view the resized images.

License

See LICENSE file for details.

Support

For issues, feature requests, or questions:

• GitHub: https://github.com/cornelha/ImageResizer.AspNetCore