在图像 (PNG) 中转换 ZPL (Base64)

Question

I need to convert a ZPL file into an image. I already use the labelary web service, but I need a solution that is less dependent on an external application.

I am proceeding in the following way. I'm getting the base64 encoded part: eJzs281u4zYQAGAKLMCewmsPhfgaPWipPtIeVUC1GPiQYx6hr9FDgdL....rest of the code (Z64 encoded), which would be the image of the ZPL file, and I'm trying to convert this to a png image. I tried using the code below, but I get this error: Error: Could not find MIME for Buffer

const fs = require('fs');
var base64Img = require('base64-img');
var Jimp = require('jimp');

try{
    var data = fs.readFileSync('./test.zpl', 'base64')
} catch (err) {
    console.log(err);
}

var buffer = Buffer.from(data, 'base64');

Jimp.read(buffer).then(res => {
    return res
    .quality(50)
    .rotate(90)
    .resize(250,250)
    .writeAsync('out.png');
}).catch(err => {
    console.log(err);
});

I tried using this method too, but it generates a png image, but it cannot be processed by the image viewer.

const fs = require('fs');
var base64Img = require('base64-img');

try{
    var data = fs.readFileSync('./test.zpl', 'base64')
} catch (err) {
    console.log(err);
}

var buffer = Buffer.from(data, 'base64');

fs.writeFileSync("./out.png", buffer);

Grateful.

Answer 1

Since you are dealing with a GRF (which is a header-less 1-bit bitmap), you will need a png-writing library to create the image - pngjs is the usual one to pull in:

const fs = require('fs'),
      zlib = require('zlib'),
      PNG = require('pngjs').PNG;


let match = /(\d+),(\d+),(\d+),:Z64:([^:]+):/
                  .exec(fs.readFileSync('test.zpl', 'ascii'));
let size = +match[1];
let rowl = +match[3];
let grf = zlib.inflateSync(Buffer.from(match[4], 'base64'));

// These values are from the ^GF command
const png = new PNG({
    width: rowl * 8,
    height: size / rowl,
    filterType: -1
});

let offs = 0;
let data = png.data;
for (let i = 0; i < size; i++) {
    let byte = grf[i];
    for (let bit = 0x80; bit; bit = bit >>> 1) {
        let bw = (bit & byte) ? 0 : 255; // black (0) or white (255)
        data[offs++] = bw;
        data[offs++] = bw;
        data[offs++] = bw;
        data[offs++] = 255;  // fully opaque
    }
}

png.pack().pipe(fs.createWriteStream('test.png'));

That is from memory and some cut and paste of existing code, so there could be a typo...