How to Convert WebP to JPEG in C#

However, if you're using C# and want to convert WebP images to another format, it can be challenging since direct support for WebP is limited in many libraries.

Google has released two DLLs, libwebp_x64.dll and libwebp_x86.dll, which can decode WebP images. However, these DLLs run native unmanaged code, so you’ll need to wrap them in a way that allows you to use them in managed code on a Windows machine.

Jose Pinero has done just that by creating a wrapper for these DLLs, allowing you to call their functionalities from C#. In this article, we'll walk you through the steps to convert a WebP image to a JPEG using C#.

Download libwebp_x64.dll, libwebp_x86.dll, and WebPWrapper.cs

To get started, you’ll need to download the following:

• libwebp_x64.dll and libwebp_x86.dll (Google's WebP library files)
• WebPWrapper.cs (a C# wrapper for the WebP DLLs)

You can find these files in the GitHub repository created by Jose Pinero: WebP Wrapper GitHub Repository

In order to handle image processing in C#, you’ll need to use the System.Drawing library, which is the standard library for image manipulation in Windows.

Install the System.Drawing.Common NuGet package to make this available in your project:

You can extend the Image class in C# to add a method for saving images as JPEGs with adjustable quality settings.

using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using Encoder = System.Drawing.Imaging.Encoder;

namespace WebPConverter
{
    public static class ImageExtensions
    {
        // Static fields to store the JPEG encoder parameters and codec
        private static readonly EncoderParameters JpegEncoderParams = new EncoderParameters(1);
        private static readonly ImageCodecInfo JpegEncoder = GetEncoder(ImageFormat.Jpeg);

        static ImageExtensions()
        {
            // Pre-define the quality encoder parameter for JPEG
            JpegEncoderParams.Param[0] = new EncoderParameter(Encoder.Quality, 80L); // Default quality (80)
        }

        public static void SaveJpeg(this Image img, string filePath, long quality = 80L)
        {
            // Update quality if needed
            JpegEncoderParams.Param[0] = new EncoderParameter(Encoder.Quality, quality);
            img.Save(filePath, JpegEncoder, JpegEncoderParams);
        }

        public static void SaveJpeg(this Image img, Stream stream, long quality = 80L)
        {
            // Update quality if needed
            JpegEncoderParams.Param[0] = new EncoderParameter(Encoder.Quality, quality);
            img.Save(stream, JpegEncoder, JpegEncoderParams);
        }

        private static ImageCodecInfo GetEncoder(ImageFormat format)
        {
            // We return the codec for the provided format
            return ImageCodecInfo.GetImageDecoders()
                .Single(codec => codec.FormatID == format.Guid);
        }
    }
}

This code will allow you to save images as JPEGs with a specified quality, either to a file or a stream.

Convert the WebP Image to JPEG

With the WebPWrapper and the ImageExtensions class in place, you can now convert a WebP image to JPEG using the following simple code:

using System.Drawing;
using WebPConverter;
using WebPWrapper;

WebP webp = new WebP();
Bitmap bitmap = webp.Load("d:\\myimg.webp");
bitmap.SaveJpeg("d:\\myimg.jpeg", 80);

This code loads a WebP image, converts it into a Bitmap, and then saves it as a JPEG with a quality setting of 80.