feat: add color options to clearBorder (#291)

Author: lpatiny

src/morphology/__tests__/clearBorder.test.ts

@@ -88,6 +88,26 @@ test('Diagonal of 1, allow corners', () => {
   ]);
 });
 
+test('Diagonal of 1, color=black', () => {
+  let image = testUtils.createMask([
+    [1, 0, 0, 0, 0],
+    [0, 1, 0, 1, 0],
+    [0, 0, 1, 0, 0],
+    [0, 0, 0, 1, 0],
+    [0, 0, 0, 0, 1],
+  ]);
+  image = image.invert();
+  let result = image.clearBorder({ color: 'black' });
+  result = result.invert();
+  expect(result).toMatchMaskData([
+    [0, 0, 0, 0, 0],
+    [0, 1, 0, 1, 0],
+    [0, 0, 1, 0, 0],
+    [0, 0, 0, 1, 0],
+    [0, 0, 0, 0, 0],
+  ]);
+});
+
 test('5x5 mask, full', () => {
   let image = testUtils.createMask([
     [1, 1, 1, 1, 1],

src/morphology/clearBorder.ts

@@ -14,6 +14,13 @@ export interface ClearBorderOptions {
    * Image to which the resulting image has to be put.
    */
   out?: Mask;
+  /**
+   * Clear either white or black area touching the border.
+   * In practice it will invert the color.
+   *
+   * @default 'white'
+   */
+  color?: 'white' | 'black';
 }
 /**
  * Set the pixels connected to the border of the mask to zero. You can chose to allow corner connection of not with the `allowCorners` option.
@@ -26,11 +33,11 @@ export function clearBorder(
   mask: Mask,
   options: ClearBorderOptions = {},
 ): Mask {
-  let { allowCorners = false, out } = options;
+  let { allowCorners = false, out, color = 'white' } = options;
   return multipleFloodFill(mask, {
     startPixels: borderIterator(mask),
-    startPixelValue: 1,
-    newPixelValue: 0,
+    startPixelValue: color === 'white' ? 1 : 0,
+    newPixelValue: color === 'white' ? 0 : 1,
     allowCorners,
     out,
   });