TextureScale.cs

// Modified from: http://wiki.unity3d.com/index.php/TextureScale#TextureScale.cs
// Only works on ARGB32, RGB24 and Alpha8 textures that are marked readable
 
using UnityEngine;

 
public class TextureScale {
    private static Color[] texColors;
    private static Color[] newColors;
    private static int w;
    private static float ratioX;
    private static float ratioY;
    private static int w2;
 
	public static Texture2D Scale(Texture2D tex, int newWidth, int newHeight) {
		texColors = tex.GetPixels();
		newColors = new Color[newWidth * newHeight];
		ratioX = 1.0f / ((float)newWidth / (tex.width-1));
		ratioY = 1.0f / ((float)newHeight / (tex.height-1));
		w = tex.width;
		w2 = newWidth;
 
		BilinearScale(0, newHeight);
 
		Texture2D resTexture = new Texture2D(newWidth,newHeight);
		resTexture.SetPixels(newColors);
		resTexture.Apply();
		return resTexture;
	}
 
	private static void BilinearScale(int start, int end) {
		for (var y = start; y < end; y++) {
			int yFloor = (int)Mathf.Floor(y * ratioY);
			var y1 = yFloor * w;
			var y2 = (yFloor+1) * w;
			var yw = y * w2;
 
			for (var x = 0; x < w2; x++) {
				int xFloor = (int)Mathf.Floor(x * ratioX);
				var xLerp = x * ratioX-xFloor;
				newColors[yw + x] = ColorLerpUnclamped(ColorLerpUnclamped(texColors[y1 + xFloor], texColors[y1 + xFloor+1], xLerp),
													   ColorLerpUnclamped(texColors[y2 + xFloor], texColors[y2 + xFloor+1], xLerp),
													   y*ratioY-yFloor);
			}
		}
	}
 
	private static Color ColorLerpUnclamped (Color c1, Color c2, float value) {
        return new Color (c1.r + (c2.r - c1.r) * value, 
						  c1.g + (c2.g - c1.g) * value, 
						  c1.b + (c2.b - c1.b) * value, 
						  c1.a + (c2.a - c1.a) * value);
    }
}