fix: 16-bit PNG encoding (#445)

rename bitDepth to depth

Author: moonayyur

src/save/__tests__/encodePng.test.ts

@@ -8,3 +8,12 @@ test('should encode what it decoded', () => {
   const imgDup = decode(encodePng(img));
   expect(imgDup).toMatchImage(img);
 });
+
+test('should encode a 16bits image correctly', () => {
+  const img = testUtils.load('formats/tif/grey16.tif');
+  expect(img.size).toBe(2700);
+  expect(img.bitDepth).toBe(16);
+  const imgDup = decode(encodePng(img));
+  expect(imgDup.bitDepth).toBe(16);
+  expect(imgDup).toMatchImage(img);
+});

src/save/encodePng.ts

@@ -14,5 +14,12 @@ export function encodePng(
   image: Image,
   options?: EncodePngOptions,
 ): Uint8Array {
-  return encode(image.getRawImage(), options);
+  const { bitDepth: depth, ...other } = image.getRawImage();
+  return encode(
+    {
+      depth,
+      ...other,
+    },
+    options,
+  );
 }