如何使图像宽度可用于transformWrite

Question

我正在尝试使用transformWrite设置FS.store，它可以扩展上传的图像。我有一个最大宽度大小。但缩放应该只是整数因子。

例如，如果我的最大宽度为100px，原始图像宽度为40px，则图像应按整数因子2缩放，这会导致目标宽度为80px（因此会导致3倍的因子）图像太宽了。）

要计算原始宽度并进行数学计算，我设置了应返回最佳宽度的函数scaleToMaxByInteger。由于某种原因，它不适用于gm转换。为什么呢？

var ScaledStore = new FS.Store.FileSystem("ScaledPix", {
    path: pathToScaledFolder,

    beforeWrite: function(fileObj, readStream) {
        return {
            extension: 'png',   // sets extension of file
            type: 'image/png'   // sets content of type field in db
        };
    },
    transformWrite: function(fileObj, readStream, writeStream) {
        // calculate max possible size if scaled by integer
        // that will fit into maximal width available
        function scaleToMaxByInteger(readStream) {
            gm(readStream)
                .size({bufferStream: true}, FS.Utility.safeCallback(function (err, size) {
                if (err) {
                    // handle the error
                } else {
                    var maxWidth = 100;
                    var originalWidth = size.width;
                    var scaleInt = Math.floor(maxWidth/originalWidth);
                    var scaleSize = scaleInt * originalWidth;

                    console.log('originalWidth: ' + originalWidth);
                    console.log('scaleInt: ' + scaleInt);
                    console.log('scaleSize: ' + scaleSize);

                    return scaleSize;
                }
            }));
        };

        // Resizing image with no antialiasing
        gm(readStream)
        .sample(scaleToMaxByInteger(readStream)) // >>>>>> This is NOT WORKING
        .stream('PNG')
        .pipe(writeStream);
    }
});