diff --git a/ui (gen4)/Makefile b/ui (gen4)/Makefile
index 10bfc443..ed778b16 100755
--- a/ui (gen4)/Makefile	
+++ b/ui (gen4)/Makefile	
@@ -35,6 +35,7 @@ LIB_DIR=lib
 EXT_LIB_DIR=ext-lib
 CSS_DIR=css
 FEATURES_DIR=features
+WORKERS_DIR=workers
 NW_PROJECT_FILE=package.json
 JS_FILES := $(wildcard *.js)
 HTML_FILES := $(wildcard *.html)
@@ -111,7 +112,7 @@ $(APP_ZIP): $(CSS_FILES) $(BUILD_DIR) $(NODE_DIR) $(NW_PROJECT_FILE) \
 	$(JS_FILES) $(CSS_FILES) $(HTML_FILES)
 	zip -r $(APP_ZIP) $(NW_PROJECT_FILE) $(JS_FILES) $(CSS_FILES) \
 		$(HTML_FILES) $(LIB_DIR) $(EXT_LIB_DIR) $(FEATURES_DIR) \
-		$(CSS_DIR) \
+		$(WORKERS_DIR) $(CSS_DIR) \
 		$(NODE_DIR)/app-module-path
 
 zip: $(APP_ZIP)
diff --git a/ui (gen4)/features/filesystem.js b/ui (gen4)/features/filesystem.js
index aeb6333c..ba7469a5 100755
--- a/ui (gen4)/features/filesystem.js	
+++ b/ui (gen4)/features/filesystem.js	
@@ -45,6 +45,41 @@ if(typeof(process) != 'undefined'){
 
 
 
+/*********************************************************************/
+
+var IndexFormat = 
+module.IndexFormat = core.ImageGridFeatures.Feature({
+	title: '',
+	doc: '',
+
+	tag: 'index-format',
+
+	config: {
+		'index-dir': '.ImageGrid',
+
+		'preview-sizes': [
+			75,
+			150,
+			350,
+			900,
+			1000,
+			1280,
+			1920,
+		],
+
+		// Supported fields:
+		// 	$INDEX			- index directory name
+		// 	$RESOLUTION		- preview resolution
+		// 	$GID			- image GID
+		// 	$NAME			- image name
+		//
+		// XXX make this used in loader too...
+		'preview-path-template': '${INDEX}/${RESOLUTION}px/${GID} - ${NAME}.jpg',
+	},
+})
+
+
+
 /*********************************************************************/
 
 var FileSystemInfoActions = actions.Actions({
@@ -67,6 +102,7 @@ module.FileSystemInfo = core.ImageGridFeatures.Feature({
 	tag: 'fs-info',
 	depends: [
 		'location',
+		'index-format',
 	],
 
 	actions: FileSystemInfoActions,
@@ -84,8 +120,6 @@ module.FileSystemInfo = core.ImageGridFeatures.Feature({
 // NOTE: this will also manage .location.from
 var FileSystemLoaderActions = actions.Actions({
 	config: {
-		'index-dir': '.ImageGrid',
-
 		'image-file-pattern': '*+(jpg|jpeg|png|JPG|JPEG|PNG)',
 
 		'image-file-read-stat': true,
@@ -1085,7 +1119,6 @@ var FileSystemWriterActions = actions.Actions({
 			'select',
 		],
 
-		'export-preview-size': 1000,
 		// XXX add options to indicate:
 		// 		- long side
 		// 		- short side
@@ -1094,12 +1127,12 @@ var FileSystemWriterActions = actions.Actions({
 		// 		- ...
 		// XXX this repeats sharp.SharpActions.config['preview-sizes']
 		'export-preview-sizes': [
-			'500',
 			'900',
 			'1000',
 			'1280',
 			'1920',
 		],
+		'export-preview-size': 1000,
 	},
 
 	// This can be:
@@ -1565,7 +1598,8 @@ module.FileSystemWriter = core.ImageGridFeatures.Feature({
 	tag: 'fs-writer',
 	// NOTE: this is mostly because of the base path handling...
 	depends: [
-		'fs-loader'
+		'fs-loader',
+		'index-format',
 	],
 	suggested: [
 		'ui-fs-writer',
@@ -1975,6 +2009,7 @@ module.FileSystemWriterUI = core.ImageGridFeatures.Feature({
 //---------------------------------------------------------------------
 
 core.ImageGridFeatures.Feature('fs', [
+	'index-format',
 	'fs-info',
 	'fs-loader',
 	'fs-writer',
diff --git a/ui (gen4)/features/sharp.js b/ui (gen4)/features/sharp.js
index c08484ec..cca5fae3 100755
--- a/ui (gen4)/features/sharp.js	
+++ b/ui (gen4)/features/sharp.js	
@@ -42,19 +42,10 @@ if(typeof(process) != 'undefined'){
 
 var SharpActions = actions.Actions({
 	config: {
-		'preview-path-template': '${INDEX}/${RESOLUTION}px/${GID} - ${NAME}.jpg',
-
 		'preview-normalized': true,
 
-		// XXX this repeats filesystem.FileSystemWriterActions.config['export-preview-sizes']
-		'preview-sizes': [
-			1920,
-			1280,
-			900,
-			350,
-			150,
-			75,
-		]
+		// NOTE: this uses 'preview-sizes' and 'preview-path-template' 
+		// 		from filesystem.IndexFormat...
 	},
 
 	// NOTE: post handlers are pushed in .makePreviews(..)
@@ -222,6 +213,8 @@ var SharpActions = actions.Actions({
 		}],
 })
 
+
+// XXX need to auto-generate previews for very large images...
 var Sharp = 
 module.Sharp = core.ImageGridFeatures.Feature({
 	title: '',
@@ -230,6 +223,7 @@ module.Sharp = core.ImageGridFeatures.Feature({
 	tag: 'sharp',
 	depends: [
 		'location',
+		'index-format',
 	],
 
 	actions: SharpActions,