PixelBox: A PictureBox with configurable InterpolationMode

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Introduction 

It's not often that we work with extremely low-resolution, or pixelated images, but when we do we may have differing expectations of what that image should look like.

In a recent project I wanted to show the pixelation of the images, but when shown in the default PictureBox, the pixelation could not be seen, because the control was smoothing the pixelation.

This is what I wanted (InterpolationType.NearestNeighbor): 

This is what I got (InterpolationType.Default): 

Background 

Windows.Forms.Controls.PictureBox is the standard control that is used to display images within a Windows Forms application. It does a decent job of this and offers some customization options, such as SizeMode, to set how an image should fit in the box.

When displaying an image at any size other than the images original size i.e. pixel-to-pixel, the extra pixels used to turn a low-resolution image into a higher one, and vise-versa have to come from somewhere. This is called interpolation, and it turns out there are many algorithms to accomplish this.

PixelBox is a custom control that is derived from PictureBox. It adds the InterpolationMode property, which has the effect of setting the GDI+ interpolation mode before the image is drawn onto the control's surface. The property is a value from the InterpolationMode enumeration.

The code 

The changes to PictureBox are quite simple. The entire class is shown below: 

using System.ComponentModel;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
 
namespace RedCell.UI.Controls
{
    /// <summary>
    /// A PictureBox with configurable interpolation mode.
    /// </summary>
    public class PixelBox : PictureBox
    {
        #region Initialization
        /// <summary>
        /// Initializes a new instance of the <see cref="PixelBox"> class.
        /// </see></summary>
        public PixelBox ()
        {
            // Set default.
            InterpolationMode = InterpolationMode.Default;
        }
        #endregion
 
        #region Properties
        /// <summary>
        /// Gets or sets the interpolation mode.
        /// </summary>
        /// <value>The interpolation mode.</value>
        [Category("Behavior")]
        [DefaultValue(InterpolationMode.Default)]
        public InterpolationMode InterpolationMode { get; set; }
        #endregion
 
        #region Overrides of PictureBox
        /// <summary>
        /// Raises the <see cref="E:System.Windows.Forms.Control.Paint"> event.
        /// </see></summary>
        /// <param name="pe" />A <see cref="T:System.Windows.Forms.PaintEventArgs"> that contains the event data. 
        protected override void OnPaint (PaintEventArgs pe)
        {
            pe.Graphics.InterpolationMode = InterpolationMode;
            base.OnPaint(pe);
        }
        #endregion
    }
}
</see>

Demonstration

The demonstration application demonstrates any of the interpolation modes on a pixelated image. In addition to those shown above, here are the other modes for comparison:

InterpolationMode.Low 

InterpolationMode.High 

InterpolationMode.Bilinear 

InterpolationMode.Bicubic 

InterpolationMode.HighQualityBilinear 

InterpolationMode.HighQualityBicubic 

Conclusion

By subclassing PictureBox and overriding its OnPaint method we can set the GDI+ InterpolationMode property, giving us greater control over the algorithm, quality, and speed of rendering.   

History

January 28, 2014

Initial publication.