I need my scaled image to be aliased in C#

Question

This might be an odd question, but when I scale my image in C# I need it to be pixelated and not anti-aliased. Just like in MSpaint when you scale.

I hope images anti-alias by default in C#, or else I changed something I didn't want to.

I've tried playing around with the Graphics.InterpolationMode but no luck there. I'm using a Bitmap object to hold the image and it's being constructed like so:

// A custom control holds the image
this.m_ZoomPanPicBox.Image = new Bitmap(szImagePath);

And a brief synapsis of the custom control:

class ZoomPanPicBox : ScrollableControl
{
    Image m_image;
    float m_zoom = 1.0f;
    InterpolationMode m_interpolationMode;
    ...
    ////////////////////////////////////////////////////////
    public ZoomPanPicBox()
    {
        //Double buffer the control
        this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.ResizeRedraw | ControlStyles.UserPaint | ControlStyles.DoubleBuffer, true);

        this.AutoScroll=true;
    }
    ////////////////////////////////////////////////////////
    protected override void OnPaint(PaintEventArgs e)
    {
        //if no image, don't bother
        if(m_image==null)
        {
            base.OnPaintBackground(e);
            return;
        }

        //Set up a zoom matrix
        Matrix mx = new Matrix(m_zoom,0,0,m_zoom,0,0);

        //now translate the matrix into position for the scrollbars
        mx.Translate(this.AutoScrollPosition.X / m_zoom, this.AutoScrollPosition.Y / m_zoom);

        //use the transform
        e.Graphics.Transform = mx;

        //and the desired interpolation mode
        e.Graphics.InterpolationMode = m_interpolationMode;

        //Draw the image ignoring the images resolution settings.
        e.Graphics.DrawImage(m_image,new Rectangle(0,0,this.m_image.Width,this.m_image.Height),0,0,m_image.Width, m_image.Height,GraphicsUnit.Pixel);

        base.OnPaint(e);
    }

Any ideas? Thanks.

Answer 1

Well, you could implement the scale yourself and do a simple linear interpolation (I.E. don't do any neighbor averaging like bicubic)... Those look nice and blocky.

Answer 2

Actually, you're right with InterpolationMode, as the docs say. Just set it to InterpolationMode.NearestNeighbor. In your code sample, you never set m_interpolationMode.