ExportTexture.cs

/// Texture exporter for Unity
/// 
/// IMPORTANT: Must be put into Editor folder to work
/// 
/// Right click on a texture in assets window and select one of 'Export/' options
/// - Use "RG Normal Map" to export normal maps as it will swap AG channels used by Unity shaders into typically used RG channels
/// 
/// Original script by Eric5h5
/// Rewritten to C# and updated by Nothke
/// 

using UnityEngine;
using UnityEditor;

public class ExportTexture
{
    [MenuItem("Assets/Export Texture/Default")]
    public static void ExportStandardChannels()
    {
        Export(false);
    }

    [MenuItem("Assets/Export Texture/RG Normal Map")]
    public static void ExportWithSwappedChannels()
    {
        Export(true);
    }

    public static void Export(bool swapNormalmapChannels)
    {
        var tex = Selection.activeObject as Texture2D;

        if (tex == null)
        {
            EditorUtility.DisplayDialog("No texture selected", "Please select a texture.", "Cancel");
            return;
        }

        // We need to set some importer settings before we export the texture
        string texPath = AssetDatabase.GetAssetPath(tex);
        TextureImporter texImport = (TextureImporter)AssetImporter.GetAtPath(texPath);

        // Save the original import settings
        bool originalIsReadable = texImport.isReadable;
        TextureImporterCompression originalCompression = texImport.textureCompression;

        // Make sure it's readable so that we can read the pixels
        texImport.isReadable = true;
        // Remove all compression because we don't want to export compressed texture
        texImport.textureCompression = TextureImporterCompression.Uncompressed;
        // Reimport the asset
        AssetDatabase.ImportAsset(texPath, ImportAssetOptions.ForceUpdate);

        // Create the new texture

        Texture2D newTexture = new Texture2D(tex.width, tex.height, TextureFormat.ARGB32, false);

        Color[] colors = tex.GetPixels();

        // Unity uses alpha channel for X component and green channel for Y,
        // but usually normal maps are encoded as R for X and G for Y,
        // so we need to SWAP CHANNELS:
        if (swapNormalmapChannels)
        {
            for (int i = 0; i < colors.Length; i++)
            {
                colors[i].r = colors[i].a;
                colors[i].a = 1;
                colors[i].b = 1;
            }
        }

        newTexture.SetPixels(colors);
        newTexture.Apply();

        // Encode to PNG
        var bytes = newTexture.EncodeToPNG();

        // Open Save panel and save it
        var path = EditorUtility.SaveFilePanel("Save Texture", "", tex.name + "_normal.png", "png");
        if (path != "")
        {
            System.IO.File.WriteAllBytes(path, bytes);
            AssetDatabase.Refresh();
        }

        // Revert to original texutre importer settings afterwards:
        texImport.isReadable = originalIsReadable;
        texImport.textureCompression = originalCompression;
        AssetDatabase.ImportAsset(texPath, ImportAssetOptions.ForceUpdate);
    }
}