EmguExtensions.Avalonia 0.1.6

EmguExtensions.Avalonia

Avalonia integration for EmguExtensions. It converts Emgu.CV.Mat images into Avalonia WriteableBitmap instances and exposes span-based access to locked Avalonia framebuffers.

Features

• Convert Mat to WriteableBitmap
• Convert grayscale, BGR, and BGRA 8-bit Mats to Avalonia Bgra8888
• Optional source color type conversion via Emgu.CV color structs
• Async conversion helpers for background image preparation
• Span and Span2D access over ILockedFramebuffer
• Row-aware access that handles framebuffer stride/padding
• Bitmap metadata helper via GetBitmapInfo()

Requirements

• .NET 10 or later
• Avalonia 12.0.4 or later
• EmguExtensions
• Emgu.CV runtime package matching your target platform

Installation

.NET CLI

dotnet add package EmguExtensions.Avalonia

NuGet Package Manager

Install-Package EmguExtensions.Avalonia

Quick Start

Convert Mat to WriteableBitmap

using Avalonia.Media.Imaging;
using Emgu.CV;
using Emgu.CV.CvEnum;
using EmguExtensions.Avalonia;

using var mat = CvInvoke.Imread("image.png", ImreadModes.Color);

WriteableBitmap bitmap = mat.ToBitmap();
PreviewImage.Source = bitmap;

ToBitmap() supports 8-bit Mats with 1, 3, or 4 channels:

• 1 channel: Gray -> BGRA
• 3 channels: BGR -> BGRA
• 4 channels: copied directly

The returned bitmap is owned by the caller. Keep it alive while UI uses it, and dispose it when replaced or no longer needed.

Convert with Explicit Source Color Type

Use this overload when the Mat channel count alone is not enough to describe the color space.

using Emgu.CV.Structure;
using EmguExtensions.Avalonia;

WriteableBitmap bitmap = hsvMat.ToBitmap(typeof(Hsv));

The srcType is passed to Emgu.CV color conversion and converted to Bgra.

Convert on Background Thread

using Avalonia.Threading;
using EmguExtensions.Avalonia;

var bitmap = await mat.ToBitmapAsync();

await Dispatcher.UIThread.InvokeAsync(() =>
{
    PreviewImage.Source = bitmap;
});

ToBitmapAsync() uses Task.Run. Assign Avalonia UI properties on the UI thread.

Framebuffer Span Access

Lock a WriteableBitmap, then use span helpers on the locked framebuffer.

using EmguExtensions.Avalonia;

using var framebuffer = bitmap.Lock();

Span2D<byte> bytes = framebuffer.GetSpan2DOfBytes();

int x = 10;
int y = 20;
int offset = x * framebuffer.BytesPerPixel;

bytes[y, offset + 0] = 255; // B
bytes[y, offset + 1] = 0;   // G
bytes[y, offset + 2] = 0;   // R
bytes[y, offset + 3] = 255; // A

For 32-bit framebuffers, pixel spans are also available:

using var framebuffer = bitmap.Lock();

Span2D<uint> pixels = framebuffer.GetSpan2D();
pixels[20, 10] = 0xFFFF0000;

Use byte spans when exact channel order matters. Avalonia Bgra8888 stores bytes as B, G, R, A.

Available Framebuffer Helpers

Metadata

using var framebuffer = bitmap.Lock();

int bytesPerPixel = framebuffer.BytesPerPixel;
int byteCount = framebuffer.ByteCount;
int pixelCount = framebuffer.PixelCount;
bool isContinuous = framebuffer.IsContinuous;

Flat Spans

using var framebuffer = bitmap.Lock();

Span<byte> allBytes = framebuffer.GetSpanOfBytes();
ReadOnlySpan<byte> readonlyBytes = framebuffer.GetReadOnlySpanOfBytes();

Span<uint> pixels = framebuffer.GetSpan();
ReadOnlySpan<uint> readonlyPixels = framebuffer.GetReadOnlySpan();

Flat pixel spans require:

• 32-bit pixel format
• continuous framebuffer memory

If the framebuffer has row padding, use GetSpan2D() or row spans.

Row Spans

using var framebuffer = bitmap.Lock();

Span<byte> rowBytes = framebuffer.GetRowSpanOfBytes(y: 5);
Span<uint> rowPixels = framebuffer.GetRowSpan(y: 5);

ROI Spans

using System.Drawing;
using EmguExtensions.Avalonia;

using var framebuffer = bitmap.Lock();

var roi = new Rectangle(10, 10, 100, 80);

Span2D<byte> roiBytes = framebuffer.GetSpan2DOfBytes(roi);
Span2D<uint> roiPixels = framebuffer.GetSpan2D(roi);

Bitmap Info

using EmguExtensions.Avalonia;

BitmapInfo info = bitmap.GetBitmapInfo();

Console.WriteLine($"{info.Width}x{info.Height}, row bytes: {info.RowBytes}");

Limitations

• Only DepthType.Cv8U Mats are supported.
• ToBitmap() supports 1, 3, and 4 channel Mats.
• Output bitmap format is always PixelFormat.Bgra8888 with AlphaFormat.Unpremul.
• A 4-channel Mat is copied directly, so it should already be BGRA-compatible.
• Framebuffer spans are valid only while the framebuffer lock is alive.
• Flat Span<uint> access requires a 32-bit continuous framebuffer. Use 2D spans for padded rows.

License

MIT. See the repository LICENSE.