描述

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

贡献者指南

技术栈: javascriptnodejs
领域: backend
议题类型: bug
难度: 3
预计时间: half day
活动状态: fresh
清晰度: clear
前置要求: JavaScript knowledgeUnderstanding of image color depth
新手友好度: 70
研究方向: Investigate the JPEG encoding module in Jimp, likely in packages/jimp/src/image/jpeg.js or similar. Locate where the color type is set during write and ensure that when the image is greyscale, the JPEG encoder uses a single channel (8 bit grayscale) instead of RGB. Check the underlying JPEG library (like jpeg js) for options to set color space. Reference the existing colorType() method for PNG as a guide.