(An Interview About) imgix Page Weight

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Imgix has been a long-time display ad sponsor here on CSS-Tricks. This post is not technically sponsored, I just noticed that they released a tool for analyzing image performance at any given URL that is pretty interesting.

We know web performance is a big deal. We know that images are perhaps the largest offender in ballooning page weights across the web. We know we have tools for looking at page performance as a whole. It seems fairly new to me to have tools for specifically analyzing and demonstrating how we could have done better with images specifically. That’s what this Page Weight tool is.

Clearly this is a marketing tool for them. You put in a URL, and it tells you how you could have done better, and specifically how imgix can help do that. I’m generally a fan of that. Tools with businesses behind them have the resources and motivation to stick around and get better. But as ever, something to be aware of.

I asked Brit Morgan some questions about it.

As we can see checking out the homepage for Page Weight, you drop in a URL, it analyzes all the images and gives you some information about how much more performant they could have been. What’s going on behind the scenes there?

We run each image on the page through imgix, resizing to fit the image container as best we can tell, and also transform file formats, color palettes, and quality breakpoints to determine which combination provides the best size savings. Then we display that version for each image.

I see it suggests fitting the image to the container, but that only makes sense for 1x displays right? Images need to be larger than their display pixel size for visual crispness on high-density display.

Definitely. The Page Weight tool does not currently address high-DPR display differences, but our service does. We offer automated high-DPR support via Client Hints, and manually via our dpr parameter, which allows developers to set the desired value directly (useful on its own or as a fallback for Client Hint support in browsers that don’t yet support that functionality). Our imgix.js front-end library also generates a comprehensive srcset (based on the defined sizes) to address whatever size/DPR the device requires.

I think most developers here are smart enough to realize this is really smart marketing for imgix. But also smart enough to realize the images are a huge deal in web performance and want to do better. What can imgix do that a developer on their own can’t do? Or that is fairly impractical for a developer to do on their own?

First, it is important to note that resizing is not the only thing that imgix does, although it is a very common use case. We provide over 100 different processing parameters that enable developers to do everything from context-aware cropping to color space handling to image compositing. So adopting imgix gives a developer access to a lot of image handling flexibility without a lot of hassle, even if they’re primarily using it to support responsive design.

That said, it is not impossible to get a very simple resizing solution running on your own, and many developers start out there. Usually, this takes the form of some kind of batch script based on ImageMagick or Pillow or some other image manipulation library that creates derivative images for the different breakpoints.

For a while, that’s often sufficient. But once your image library gets beyond a few hundred images, batch-based systems begin to break down in various ways. Visibility, error handling, image catalog cleaning, and adding support for new formats and devices are all things that get much harder at scale. Very large sites and sites where content changes constantly will often end up spending significant dev time on these kinds of maintenance tasks.

So really, „could you build this?” is a less useful question than „should you build this?” In other words, is image processing central enough to the value proposition of what you’re building that you’re willing to spend time and effort maintaining your own system to handle it? Usually, the answer is no. Most developers would rather focus on the what’s important and leave images to something like imgix — a robust, scaleable system that just works.

Does the tool look at responsive images syntax in HTML? As in, which image was actually downloaded according to the srcset/sizes or picture element rules?

Not yet. That’s a feature we’re hoping to implement in the next version of the tool.

Can you share implementations of imgix that are particularly impressive or creative?

An interesting use we see more and more is image processing for social media. These days, many sites see the majority of their traffic coming in through social, which makes it more important than ever to make content look good in the feed. Setting OpenGraph tags is a start, but every social network has a different container size. This creates a similar problem to the one posed by mobile fragmentation, and we can help by dynamically generating social images for each network. This provides a polished presentation without adding a ton of overhead for the person maintaining the site.

Other customers are pushing even further by combining several images to create a custom presentation for social. HomeChef, a meal delivery service, does this to dynamically create polished, branded images for Pinterest from their ingredient photos.

We actually created an open source tool called Motif (GitHub Repo) to make it easier for developers to get started with dynamically generating social images through imgix.


(An Interview About) imgix Page Weight is a post from CSS-Tricks

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