Base64-encoded JPEG images generated in Java and other programming languages may appear broken when decoded in .NET. This may occur due to multiple reasons including ICC profile related issues or the colorspace used by the encoder. To ensure compatibility, images should either be converted to RGB before encoding in the source system or decoded in .NET using proper color management. In .NET Framework 4.8, embedded ICC profiles can be honored with Image.FromStream(stream, true, true), while in .NET Core 8 and later, libraries like Magick.NET provide consistent CMYK-to-RGB conversion during image loading.

The Problem: Base64 encoded JPEGs in .NET May Appear Broken

When .NET code attempts to decode a Base64 JPEG, an exception may be thrown or a broken tag may appear in the browser. The issue is not related to Base64 formatting but stems from a color space incompatibility.

Java’s toJpeg(...) method often emits CMYK‑encoded JPEGs for print‑quality images. Java’s imaging libraries decode CMYK without trouble, but .NET’s GDI+ (System.Drawing) has very limited, and often broken, CMYK support.

GDI+ will either fail silently or throw ArgumentException: Parameter is not valid when encountering a CMYK JPEG, causing the browser to render a broken image icon.

Solution Path A – Embedded Color Management in .NET Framework 4.8

Why
GDI+ can apply ICC profiles if you call Image.FromStream with embedded color management enabled.

Full Console Example for .NET 4.8

// Requires no extra NuGet on .NET Framework 4.8
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

namespace ImageDecoderConsole
{
    class Program
    {
        static void Main()
        {
            const string rawBase64 = "…YOUR_BASE64_STRING_HERE…";

            string cleaned = rawBase64
                .Replace("\r","")
                .Replace("\n","")
                .Replace(" ","")
                .Trim();

            byte[] jpegBytes;
            try 
            {
                jpegBytes = Convert.FromBase64String(cleaned);
            }
            catch (FormatException fe)
            {
                Console.Error.WriteLine("Invalid Base64: " + fe.Message);
                return;
            }

            try
            {
                using var msIn = new MemoryStream(jpegBytes);
                using var img = Image.FromStream(
                    msIn,
                    useEmbeddedColorManagement: true,
                    validateImageData: true
                );
                string outputFile = Path.Combine(
                    Environment.CurrentDirectory,
                    "decoded_output.jpg"
                );
                img.Save(outputFile, ImageFormat.Jpeg);
                Console.WriteLine($"Saved to {outputFile}");
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine("Decoding failed: " + ex.Message);
            }
        }
    }
}

Solution Path B – Third Party Library

Why
System.Drawing (based on GDI+) fails to reliably decode CMYK JPEGs, especially when ICC profiles are involved. This results in broken images or runtime errors. Magick.NET is a fully managed, cross-platform image processing library that correctly handles CMYK color space and automatically converts images to RGB when needed, ensuring consistent rendering across environments.

.NET Framework 4.8 with ImageMagick

// Install via:
//   Install-Package Magick.NET-Q8-AnyCPU

using System;
using System.IO;
using ImageMagick;

namespace DotNet48MagickDecoder
{
    class Program
    {
        static void Main()
        {
            const string rawBase64 = "…YOUR_BASE64_STRING_HERE…";

            string cleaned = rawBase64
                .Replace("\r", "")
                .Replace("\n", "")
                .Replace(" ", "")
                .Trim();

            byte[] jpegBytes;
            try
            {
                jpegBytes = Convert.FromBase64String(cleaned);
            }
            catch (FormatException fe)
            {
                Console.Error.WriteLine("Invalid Base64: " + fe.Message);
                return;
            }

            try
            {
                using var image = new MagickImage(jpegBytes);

                if (image.ColorSpace == ColorSpace.CMYK)
                {
                    image.ColorSpace = ColorSpace.sRGB;
                }

                string outputFile = Path.Combine(
                    AppDomain.CurrentDomain.BaseDirectory,
                    "output_48.jpg"
                );

                image.Write(outputFile);
                Console.WriteLine("Image saved to: " + outputFile);
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine("Image decode failed: " + ex.Message);
            }
        }
    }
}

Cross-Platform in .NET Core 8+ with ImageMagick

// Install via:
//   dotnet add package Magick.NET-Q8-AnyCPU

using System;
using System.IO;
using ImageMagick;

namespace DotNet8MagickDecoder
{
    class Program
    {
        static void Main()
        {
            const string rawBase64 = "…YOUR_BASE64_STRING_HERE…";

            string cleaned = rawBase64
                .Replace("\r", "")
                .Replace("\n", "")
                .Replace(" ", "")
                .Trim();

            byte[] jpegBytes;
            try
            {
                jpegBytes = Convert.FromBase64String(cleaned);
            }
            catch (FormatException fe)
            {
                Console.Error.WriteLine("Invalid Base64: " + fe.Message);
                return;
            }

            try
            {
                using var image = new MagickImage(jpegBytes);

                if (image.ColorSpace == ColorSpace.CMYK)
                {
                    image.ColorSpace = ColorSpace.sRGB;
                }

                string outputFile = Path.Combine(
                    Directory.GetCurrentDirectory(),
                    "output_net8.jpg"
                );

                image.Write(outputFile);
                Console.WriteLine("Image saved to: " + outputFile);
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine("Image decode failed: " + ex.Message);
            }
        }
    }
}

Conclusion

By understanding that GDI+ does not handle JPEG color management related issues by default and applying either embedded color management or a cross‑platform library, you can reliably decode Base64 JPEGs in .NET.