The Unity3D Asset Pipeline.

One of the great things about Unity3D, is the programmable content pipeline. I wrote this script so that when I add a texture named "x_SPECULAR.png" to my project, it looks for a texture named "x_DIFFUSE.png", and then copies the specular texture into the alpha channel of the diffuse texture (so that it can be used in a Unity3D specular shader). This automates what would usually be a tedious Photoshop task.

using UnityEngine;
using UnityEditor;
using System.Collections;

class ModifyTextures : AssetPostprocessor
{

 void OnPostprocessTexture (Texture2D texture)
 {
  if (assetPath.Contains ("_SPECULAR")) {
   var diffusePath = assetPath.Replace ("_SPECULAR", "_DIFFUSE");
   var bytes = System.IO.File.ReadAllBytes (diffusePath);
   var diffuse = new Texture2D (texture.width, texture.height);
   diffuse.LoadImage (bytes);
   var colors = diffuse.GetPixels ();
   var specular = texture.GetPixels ();
   if (colors.Length == specular.Length) {
    Debug.LogWarning (assetPath + ": Adding specular values to diffuse map alpha.");
    for (var i = 0; i < colors.Length; i++) {
     colors[i].a = (specular[i].r + specular[i].g + specular[i].b) / 3;
    }
    diffuse.SetPixels (colors);
    diffuse.Apply ();
    System.IO.File.WriteAllBytes (diffusePath, diffuse.EncodeToPNG ());
    AssetDatabase.ImportAsset (diffusePath);
    AssetDatabase.DeleteAsset(assetPath);
   } else {
    Debug.LogWarning (assetPath + ": specular size must match diffuse size.");
   }
   return;
  }
 }
}