started working on issue #2

src/Filter.ts

@@ -256,9 +256,18 @@ var FILTER_TYPES: {
         }
     ];
 
-export function filter(imageData: ImageData): Uint8Array {
-    const {width, height, data} = imageData;
-    const bpp = 4; //bits per pixel r,g,b,a
+export function filter(imageData: ImageData, colorType: number): Uint8Array {
+    var {width, height} = imageData;
+    var data:number[] | Uint8Array = imageData.data;
+    if (colorType !== 6) {
+        var temp = new Uint8Array(width * 3 * height);
+        for (var fromI=0, toI=0; fromI < data.length; fromI+= 4, toI+=3){
+            PngWriter.copy(data, temp, toI, 3, fromI);
+        }
+        data = temp;
+    }
+
+    const bpp = colorType === 6 ? 4 : 3; //bits per pixel r,g,b,a or r,g,b
     const byteWidth = width * bpp; //r,g,b,a
     var filtered = new Uint8Array((byteWidth + 1) * height);
     var filterTypePos = 0;

src/PngWriter.ts

@@ -11,10 +11,12 @@ export class PngWriter {
 
     write(imageData: ImageData, options?: PakoOptions) {
         options = options || {};
+        var {colorType} = options;
+        colorType = colorType || 6;
         var parts: Uint8Array[] = [];
         parts.push(new Uint8Array(PngWriter.PNG_SIGNATURE));
-        parts.push(this.writeIHDRChunk(imageData.width, imageData.height));
-        var filtered = filter(imageData);//this._filterData(imageData);
+        parts.push(this.writeIHDRChunk(imageData.width, imageData.height, colorType));
+        var filtered = filter(imageData, colorType);//this._filterData(imageData);
         var compressed = pako.deflate(filtered, Object.assign({
             /**
              * //compression level 0-9
@@ -59,13 +61,14 @@ export class PngWriter {
      * Creates IHDR chunk (image dimensions, color depth, compression method, etc.)
      * @param width of png image
      * @param height of png image
+     * @param color type of image ()
      */
-    private writeIHDRChunk(width: number, height: number): Uint8Array {
+    private writeIHDRChunk(width: number, height: number, colorType: number): Uint8Array {
         var ihdr = new Uint8Array(13);
         PngWriter._writeAsBigEndian(ihdr, width, 0);
         PngWriter._writeAsBigEndian(ihdr, height, 4);
         ihdr[8] = 8;  // Bit depth: 8 bits per sample //todo add this as option maybe (need to recalculate bpp for this)
-        ihdr[9] = 6;  // Color type: 6 = RGBA // todo add this as option maybe (need to recalculate bpp for this)
+        ihdr[9] = colorType;  // Color type: 6 = RGBA // todo add this as option maybe (need to recalculate bpp for this)
         ihdr[10] = 0;  // Compression method: DEFLATE (pako comes handy)
         ihdr[11] = 0;  // Filter method: Adaptive
         ihdr[12] = 0;  // Interlace method: None

typings/tsd.d.ts

@@ -35,5 +35,6 @@ interface PakoOptions {
     level?: number,
     windowBits?: number,
     chunkSize?: number,
-    strategy?: number
+    strategy?: number,
+    colorType?: number
 }