CollectionFS get image dimensions before transformation

Question

I would like to resize image upon upload with Meteor CollectionFS. But I would like to resize based on image dimensions. For example, I want to resize image that is 1000x500 into 1024x512, but 60x100 into 64x128 - for that I need to know source dimensions.

I am basing my code on one provided by CollectionFS documentation:

var createThumb = function(fileObj, readStream, writeStream) {
  // Transform the image into a 10x10px thumbnail
  gm(readStream, fileObj.name()).resize('10', '10').stream().pipe(writeStream);
};

how do I get source dimensions here, to make my resize target dynamic? Maybe there are some graphicsmagick function?

Answer 1

There's an async GraphicsMagick function for returning the size (dimensions) of the image.

gm(readStream).size({ bufferStream: true }, function(err, value) {
    var w = 100, h = 100;

    //modify logic here to set the desired output width/height, based on the source width/height
    if (value.width == 60 && value.height == 100) {
         w = 64;
         h = 128;
    }

    //"this" is the gm context, so you can chain gm functions to "this" inside the size callback.
    this.resize(w, h).stream().pipe(writeStream);
});

Notes from the gm npm package page on Github regarding this:

GOTCHA: when working with input streams and any 'identify' operation (size, format, etc), you must pass "{bufferStream: true}" if you also need to convert (write() or stream()) the image afterwards NOTE: this buffers the readStream in memory!