C# Image Edge Feathering

Question

Hi Everyone,

DISCLAIMER: This code is terrible and should not be used in production. It's testing a proof of concept.

I want to create an image like below using C# the key points are the feathered edges and the transparency of the whole image.

Here is my result so far

As you can see the edges are feathered. My question is, does anyone know how to feather the edges using pure C# and maintain transparency, currently I am using a 3rd party library with some pretty nasty looking code?

Would be interested if there is a better approach to this full stop.

Here is some of the code I have been using.

Bitmap bitmap = new Bitmap(width, height);
Graphics graphics = Graphics.FromImage(bitmap);
// Transparent Background
SolidBrush semiTransparentPen = new SolidBrush(Color.FromArgb(60, 31, 31, 31));
graphics.FillRectangle(semiTransparentPen, 0f, 0f, bitmap.Width, bitmap.Height);

// Feather edges
Bitmap bitmap1 = new Bitmap(bitmap);
Bitmap bitmap2 = new Bitmap(bitmap);

fipbmp.makeEdgesTransparentHorzSigma(bitmap1, 4, 4);
fipbmp.makeEdgesTransparentVertSigma(bitmap2, 4, 4);
fipbmp.MergeBmp(bitmap, bitmap1, bitmap2);

MemoryStream memoryStream = new MemoryStream();
bitmap.Save(memoryStream, ImageFormat.Png);

byte[] buffer = memoryStream.ToArray();

Answer 1

You may find this blog post which I once wrote useful: Soft Edged Images in GDI+. That will show you a lot of what you need to know. In order to create smooth edges on an arbitrary shape you will also need a smoothing filter (which you'll then need to apply to the alpha channel), which you can read about here.