Progressive image rendering

 

 

PROGRESSIVE IMAGE RENDERING

@jmperezperez

About me

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Page Load Time

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@jmperezperez

Version A

JSDayES

Madrid

2017

Speakers & Schedule

0.0s

0.3s

0.6s

0.9s

1.2s

Version B

JSDayES

Madrid

2017

Speakers & Schedule

0.0s

0.3s

0.6s

0.9s

1.2s

JSDayES

Madrid

2017

Speakers & Schedule

JSDayES

Madrid

2017

JSDayES

Madrid

2017

PROGRESSIVE IMAGE RENDERING

@jmperezperez

User Perceived Performance

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Speed Index = \int_0^{end} 1 - \frac{VC}{100}
SpeedIndex=0end1VC100Speed Index = \int_0^{end} 1 - \frac{VC}{100}

end = end time in milliseconds

VC = % visually complete

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WebPageTest

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More kilobytes

 

improved perceived performance

can sometimes lead to

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Avoiding this:

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Techniques to improve perceived performance

  • Server-side rendering
  • Critical CSS
  • Async JS
  • Async fonts

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What about images?

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images

1712kB (66%)

scripts

426kB (16%)

other

464kB (18%)

source: http archive 15 apr 2017

To use or not to use images

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Minimalist | Flat Design

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Not that long ago

Optimise your images

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TIP 1

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right format

gif | png | jpg | webp | <the_next_thing>

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<picture>
    <source type="image/webp" srcset="2700x1209/my-image.webp 2700w, 
                    1024x1024/my-image.webp 1024w, 
                    600x600/my-image.webp 600w" 
            sizes="100vw" />
    <source srcset="2700x1209/my-image.jpg 2700w, 
                    1024x1024/my-image.jpg 1024w, 
                    600x600/my-image.jpg 600w" 
            sizes="100vw" />
    <img class="rsImg" src="600x600/my-image.jpg" alt="My beautiful image" />
</picture>

compression

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· lossless

· perceptual

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1 column

2 columns

3 columns

Responsive

TIP 2

<img sizes="(max-width: 30em) 100vw,
            (max-width: 50em) 50vw,
            calc(33vw - 100px)"
     srcset="profile-200.jpg 200w,
             profile-400.jpg 400w,
             profile-800.jpg 800w,
             profile-1600.jpg 1600w"
     src="profile-400.jpg" alt="Pinchito">

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Challenge: Keeping in sync markup and CSS

Example

RESPONSIVE IMAGES

Lazy-load images

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TIP 3

<img> above the fold

&

Lazy below the fold

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Intersection

Observer

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// load image when it's within 100px of the viewport

const options = {
  rootMargin: '100px'
}

const callback = entries => { 
  entries.forEach(entry => {
    if (entry.intersectionRatio > 0) {
        // load image
    }
  });
};

const observer = new IntersectionObserver(callback, options);
observer.observe(document.querySelector('.lazy-img'));

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Example

INTERSECTION OBSERVER

class LazyImage extends React.Component {

    constructor() {
        this.observer = new IntersectionObserver(entries => {
            if (entries[0].intersectionRatio > 0) {
                // load!
            }
        });
        this.element = null;  /* render() will set it through a ref */
    }

    componentDidMount() {
        this.observer.observe(this.element);
    }

    componentWillUnmount() {
        this.observer.unobserve(this.element);
    }
    ...
}

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Encapsulating in React

INTERSECTION OBSERVER

What to show while the image is loading

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Options

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PLACEHOLDERS

Nothing

Placeholder

Solid colour

Progressive image loading or "Blur-up"

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Examples of solid color

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PROGRESSIVE IMAGE RENDERING

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PROGRESSIVE IMAGE RENDERING

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Examples of

Progressive Image Loading

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Medium

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Medium

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Quartz (qz.com)

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Quartz (qz.com)

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Quora

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How it is done

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Markup - Eg Medium

<figure>
  <div>

    <div/> <!-- this div keeps the aspect ratio so
                the placeholder doesn't collapse -->

    <img/> <!-- this is a tiny image with a small
                resolution (e.g. ~27x17) and low quality -->

    <canvas/> <!-- takes the above image and applies a blur filter -->

    <img/> <!-- the large image to be displayed -->

    <noscript/> <!-- fallback for no JS -->

  </div>
</figure>

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Progressive JPEGs

Baseline

Progressive

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With the Progressive JPEG method [...] cognitive fluency is inhibited and the brain has to work slightly harder to make sense of what is being displayed.

— From Progressive image rendering: Good or evil?

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Facebook

Inlining thumbnail image in payload

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Facebook

 

Unfortunately, the standard JPEG header is hundreds of bytes in size. In fact, the JPEG header alone is several times bigger than our entire 200-byte budget. However, excluding the JPEG header, the encoded data payload itself was approaching our 200 bytes.

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Facebook

Header (Quantization Table and Huffman Table) Compressed
Data

Client (mobile app)                                                GraphQL

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Thumbnails

Getting creative with SVGs

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SVG

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SVG

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Drawing with SVG

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Drawing bitmap images

Canny Edge Detector

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<svg>
  <polyline points="51,1 61,1 61,2 56,4 56,3"/>
  <polyline points="52,1 50,2 51,3 50,4 50,9 46,10 46,8 48,8 48,9"/>
  <polyline points="61,4 61,5 58,6"/>
  ...
  <polyline points="62,58 61,59 61,60 50,62 50,61 51,61"/>
</svg>
  1. Find edges with canny edge detector
  2. Create lines
  3. Use JS and SVG to animate

How to draw bitmaps

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Should we do this?

Just because you can it doesn't mean you should

PROGRESSIVE IMAGE RENDERING

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  • Reduce requests
  • Choose the right format and optimise
  • Embrace responsive images
  • Try to lazy load
  • Innovate!

Summary

The Web is fun.

PROGRESSIVE IMAGE RENDERING

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talk with me for more info

Thanks!

@jmperezperez

Progressive Image Rendering

By José M. Pérez

Progressive Image Rendering

This talk addresses the culprit in page size, images. I feel that we like discussing JS and CSS and its payload, but we tend to forget about images, which represent 2/3 of the bytes of a page. The most performant request is the one that is never done, and this beats any possible image optimization. There are some common scenarios in which we can avoid using images, being adopting a minimalism/flat design or hiding certain images on smaller screens. Of course, we will need to use some images eventually. For these cases I explain how the picture element might help and some of its limitations I have found when working with real websites. One of them is lazy loading of images, which can bring great savings in terms of data traffic, but it is also easy to implement wrongly. Lastly I show some techniques to "fill" the space for an image while it is loaded, going from just showing an empty area to doing a progressive loading from a blurry image.

  • 3,340

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