Expected Behavior

When writing images to disk after calling greyscale() method should produce 8-bit PNGs and JPEGs.

Current Behavior

Even when greyscale() is called images are still 24 or 32 BPP. After some digging I've discovered that you can get 8-bit PNGs by leveraging the colorType() method. Unfortunately no such thing for JPEGs.

Steps to Reproduce

Jimp.read('image.png').then(image => {
  image.greyscale().write('image_greyscale.png');
});

Jimp.read('image.jpg').then(image => {
  image.greyscale().write('image_greyscale.jpg');
});

Context

• Jimp Version: 0.14
• Operating System: Windows 10
• Node version: 12