Determining Total Image Load Time


I want to calculate the total time a site spent loading images using the JSON API.

My plan is to loop through the median->firstView->requests node, isolate the images and sum the image load time from one of the metrics in there, but there are a number relating to load time. I just don’t know what to use. I tried all_ms, but that actually generated a load time greater than the page load time.


                                   "load_end": 947,
				"ttfb_start": "854",
				"ttfb_end": 947,
				"download_start": 947,
				"download_end": 947,
				"download_ms": 0,
				"all_start": "769",
				"all_end": 947,
				"all_ms": 178,

Resources download concurrently so you can’t just add up the times for individual resources. When you look at the waterfall the overlapping bars are the times, otherwise it would look like a stair-step the whole way.