Get object from S3 in AWS Lambda function and send to Api Gateway

I am trying to get a .jpg file from a bucket and send it back to api gateway. I believe I have the setup correct as I see stuff being logged. It grabs the file from s3 fine, and gm is the graphicsmagick library. Not sure if I am using it right though.

In the lambda function I do this (alot of the code comes from the aws example):

async.waterfall([
    function download(next) {
        console.log(srcKey);
        console.log(srcBucket);
        // Download the image from S3 into a buffer.
        s3.getObject({
                Bucket: srcBucket,
                Key: srcKey
            },
            next);
        },
    function transform(response, next) {
        console.log(response);
        next(null, 'image/jpeg', gm(response.Body).quality(85));

    },

    function sendData(contentType, data, next){
        console.log(contentType);
        console.log(data);
        imageBuffer = data.sourceBuffer;
        context.succeed(imageBuffer);
    }
    ]
);

The response header has content-length: 85948, which doesn't seem right because the original file is only 36kb. Anyone know what I'm doing wrong?