Demo

Direction

1. Open your pixel that you want to stretch.

2. Select Rectangle Marquee Tool ().

3. Drag to cover your pixel > Edit > Copy.

4. File > New > if you want to stretch vertically, stick with the width and only change the height (do it vice versa if you want to stretch horizontally).

5. Edit > Paste > move your pixel to the topmost.

6. Select Single Row Marquee Tool ().

7. Click on your pixel where you want to start stretching.

8. Click Ctrl + T.

9. Select one of the square points and drag it down to the bottom of the document.

10. Click Ctrl + D (deselect).

11. Done. :-)