InterpolationMode HighQualityBicubic introducing artefacts on edge of resized images

Question

Using some pretty stock standard C# code to resize an image, and place it on a coloured background

Image imgToResize = Image.FromFile(@\"Dejeuner.jpg\");
Siz         


        

Answer 1

Below is the resulting image of typical HighQualityBicubic resizing (drawn over white background).

You can see semi-transparent pixels at edge lines. You can call it a bug. I think it is just a technical detail of the GDI+. And it is simple to workaround this artifact.

1) Prevent anti-aliasing.

...
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
// add below line
g.CompositingMode = CompositingMode.SourceCopy;
...

With CompositingMode.SourceCopy result image will show visible outline but not anti-aliased with background pixels.

2) Crop semi-transparent area

You can ignore those semi-transparent pixels altogether.

Image imgToResize = Image.FromFile(@"Dejeuner.jpg");
Size size = new Size(768, 1024);
Bitmap b = new Bitmap(size.Width, size.Height);

Graphics g = Graphics.FromImage((Image)b);
g.FillRectangle(Brushes.Green, 0, 0, size.Width, size.Height);

Bitmap b2 = new Bitmap(768 + 8, 570 + 8);
{
    Graphics g2 = Graphics.FromImage((Image)b2);
    g2.Clear(Color.White);
    g2.InterpolationMode = InterpolationMode.HighQualityBicubic;
    g2.DrawImage(imgToResize, new Rectangle(2, 2, 768 + 4, 570 + 4));
}

g.CompositingMode = CompositingMode.SourceCopy;
g.DrawImage(b2, 0, 150, new Rectangle(4, 4, 768, 570), GraphicsUnit.Pixel);
b.Save("sized_HighQualityBicubic.jpg");

Answer 2

Set the PixelOffsetMode property to HighQuality to get a better blend with the background at the edges.

Answer 3

Shamelessly lifting the answer from this question, I found this fixes it:

using (ImageAttributes wrapMode = new ImageAttributes())
{
    wrapMode.SetWrapMode(WrapMode.TileFlipXY);
    g.DrawImage(input, rect, 0, 0, input.Width, input.Height, GraphicsUnit.Pixel, wrapMode);
}