1st You have to install "Imagemagick"

1. For windows, you will find .exe file. Keep it in your mind that on installation time, check "Install legacy utilities (e.g: convert)"

2. For Ubuntu:

sudo apt install imagemagick

1. For Cent OS:

sudo yum install ImageMagick

Now Check the Sample Code given below.
var fs=require('fs');
var spawn = require('child_process').spawn;
//ifile: Tiff Absolute File Path
//ofile: PNG Absolute File Path (e.g: var ofile = APP_ROOT_PATH+'/data/files/png/sample.png';)
var tiff2png = spawn('convert', [ifile, ofile]);
tiff2png.stdout.on('data', function (data) {
    console.log('stdout: ' + data);
});
tiff2png.stderr.on('data', function (data) {
    return res.json(Utility.output('Unable to convert tiff to png','ERROR'));
    console.log('stderr: ' + data);
});
tiff2png.on('close', function (code) {
    /**Check Your Converted file exist or not. If exist then Converted**/
    console.log('Close: ' + data);
});
tiff2png.on('error', function (code) {
    return res.json(Utility.output('ERROR: Unable to convert tiff to png','ERROR'));
});