Image opacity

One exampple of how to change image opacity:

private Image SetImageOpacity(Image image, float opacity)
{
	try
	{
		//create a Bitmap the size of the image provided  
		Bitmap bmp = new Bitmap(image.Width, image.Height);

		//create a graphics object from the image  
		using (Graphics gfx = Graphics.FromImage(bmp))
		{

			//create a color matrix object  
			ColorMatrix matrix = new ColorMatrix();

			//set the opacity  
			matrix.Matrix33 = opacity;

			//create image attributes  
			ImageAttributes attributes = new ImageAttributes();

			//set the color(opacity) of the image  
			attributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);

			//now draw the image  
			gfx.DrawImage(image
				, new Rectangle(0
					, 0
					, bmp.Width
					, bmp.Height
				)
				, 0
				, 0
				, image.Width
				, image.Height
				, GraphicsUnit.Pixel
				, attributes
			);
		}

		return bmp;
	}
	catch (Exception ex)
	{
		MessageBox.Show(ex.Message);
		return null;
	}
}

My example how use this method:

try
{
	float opacity = (float) trackBar1.Value / 100;
	panel1.BackgroundImageLayout = ImageLayout.Center;
	panel1.BackgroundImage = SetImageOpacity(myBitmap, opacity);
}
catch (Exception exception)
{
	MessageBox.Show($@"Cannot to set opacity of picture. Error message: {exception.Message}");
}

Notice that opacity is float and it can be between 0 to 1, everything bigger then 1 will have no impact. Example in Winforms you can download from here.

Taken from here.