diff --git a/src/ide/pixeleditor.ts b/src/ide/pixeleditor.ts
index 21e58819..909a76b2 100644
--- a/src/ide/pixeleditor.ts
+++ b/src/ide/pixeleditor.ts
@@ -27,22 +27,23 @@ export type SelectableTilemap = {
 }
 
 export type PixelEditorImageFormat = {
-  w:number
-  h:number
-  count?:number
-  bpp?:number
-  np?:number
-  bpw?:number
-  sl?:number
-  pofs?:number
-  remap?:number[]
-  reindex?:number[]
-  brev?:boolean
-  flip?:boolean
+  w:number		// width
+  h:number		// height
+  count?:number		// # of images
+  bpp?:number		// bits per pixel
+  np?:number		// number of planes
+  bpw?:number		// bits per word
+  sl?:number		// words per line
+  pofs?:number		// plane offset
+  remap?:number[]	// remap array
+  reindex?:number[]	// reindex array
+  brev?:boolean		// bit reverse (msb is leftmost)
+  flip?:boolean		// flip vertically
+  skip?:number		// skip bytes
+  wpimg?:number		// words per image
+  aspect?:number	// aspect ratio
+  xform?:string		// CSS transform
   destfmt?:PixelEditorImageFormat
-  xform?:string
-  skip?:number
-  aspect?:number
 };
 
 export type PixelEditorPaletteFormat = {
@@ -162,12 +163,13 @@ export function convertWordsToImages(words:UintArray, fmt:PixelEditorImageFormat
   var mask = (1 << bpp)-1;
   var pofs = fmt.pofs || wordsperline*height*count;
   var skip = fmt.skip || 0;
+  var wpimg = fmt.wpimg || wordsperline*height;
   var images = [];
   for (var n=0; n<count; n++) {
     var imgdata = [];
     for (var y=0; y<height; y++) {
       var yp = fmt.flip ? height-1-y : y;
-      var ofs0 = n*wordsperline*height + yp*wordsperline;
+      var ofs0 = wpimg*n + yp*wordsperline;
       var shift = 0;
       for (var x=0; x<width; x++) {
         var color = 0;
@@ -202,19 +204,22 @@ export function convertImagesToWords(images:Uint8Array[], fmt:PixelEditorImageFo
   var mask = (1 << bpp)-1;
   var pofs = fmt.pofs || wordsperline*height*count;
   var skip = fmt.skip || 0;
+  var wpimg = fmt.wpimg || wordsperline*height;
+  
   var words;
   if (nplanes > 0 && fmt.sl) // TODO?
-    words = new Uint8Array(wordsperline*height*count);
+    words = new Uint8Array(wpimg*count);
   else if (bitsperword <= 8)
-    words = new Uint8Array(wordsperline*height*count*nplanes);
+    words = new Uint8Array(wpimg*count*nplanes);
   else
-    words = new Uint32Array(wordsperline*height*count*nplanes);
+    words = new Uint32Array(wpimg*count*nplanes);
+
   for (var n=0; n<count; n++) {
     var imgdata = images[n];
     var i = 0;
     for (var y=0; y<height; y++) {
       var yp = fmt.flip ? height-1-y : y;
-      var ofs0 = n*wordsperline*height + yp*wordsperline;
+      var ofs0 = n*wpimg + yp*wordsperline;
       var shift = 0;
       for (var x=0; x<width; x++) {
         var color = imgdata[i++];
@@ -455,7 +460,7 @@ export class TextDataNode extends CodeProjectDataNode {
   }
   updateLeft() {
     if (this.right.words.length != this.words.length)
-      throw Error("Expected " + this.right.words.length + " bytes; image has " + this.words.length);
+      throw Error("Cannot put " + this.right.words.length + " image bytes into array of " + this.words.length + " bytes");
     this.words = this.right.words;
     // TODO: reload editors?
     var datastr = this.text.substring(this.start, this.end);
@@ -1072,7 +1077,12 @@ class PixEditor extends Viewer {
 
   commit() {
     this.updateImage();
-    this.left.refreshLeft();
+    try {
+      this.left.refreshLeft();
+    } catch (e) {
+      console.log(e);
+      alert(`Could not update source code. ${e}`);
+    }
   }
 
   remapPixels(mapfn : (x:number,y:number) => number) {