Stops Unity from compressing textures on import (must reset any existing texture imports to take effect, or group select and set compression to "none"). Drag this file into Assets/Plugins/Editor (make the folders if they don't exist already)

NoDXT.cs

using UnityEditor;
using UnityEngine;

public class NoDXT : AssetPostprocessor
{
   void OnPreprocessTexture() {
        var importer = (TextureImporter)assetImporter;
        importer.textureCompression = TextureImporterCompression.Uncompressed;
   }
}