CSS and image optimization

CSS and Image Optimization Stoyan Stefanov, @stoyanstefanov May 12, 2010 Web Optimization Summit

Agenda 1.  Reducing CSS file sizes 2.  Rendering 3.  Reducing HTTP requests 4.  Optimizing image file sizes

Reducing CSS file sizes

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; }

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Long selectors

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } C-style indented declarations

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } What? Not unique enough?

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } One is probably enough

CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Lame

Crockford on CSS: “Long, fragile lists of self-contradictory rules”

So? #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Legend: • easy stuff • tough stuff

So? Make the tough stuff easy

Reusable CSS .linklist {color: green; ...} /* widgets */ .module {...} .gallery {...} /* utilities */ .clearfix {...}; .flip {...}

Mixin pattern <ul class="module linklist"> …

Reusable CSS 1.  Strong foundation: reset, grids 2.  Library styles: .class not #id

Object-Oriented CSS •  Nicole Sullivan •  oocss.org

Minifying CSS •  Strip white space, comments •  Some micro-optimizations •  ~30% savings •  can’t rename •  YUICompressor, CSSTidy •  Inline code too! http://tools.w3clubs.com/cssmin/

Browser-specific CSS •  IE6,7 vs. others •  -webkit-, -moz-, -o- •  -ms-, _, *, zoom •  automated •  savings? 3-5%, mileage vary http://phpied.com/files/css-parse/css-strip.html

CSS and rendering

Filters •  AlphaImageLoader is bad •  Verdict is out on the others

Expressions •  Executed too often •  Avoid •  JavaScript or self-rewrite

Behaviors •  Be careful with the shims •  ie-css3.htc, pngfix.htc,…

Scrollbars trick •  Prevent a reflow when you expect a long page body {overflow-y: scroll;}

Reducing HTTP requests

CSS blocks rendering •  The worst component type •  Place way at the top •  Inline all @media print, etc http://www.phpied.com/delay-loading-your-print-css/ http://www.phpied.com/rendering-styles/

Same domain •  If you split across domains, keep CSS on the same domain as HTML

Inline CSS •  Google search •  Bing.com: inline + postload

Inline + postload •  First visit: 1. Inline 2. Lazy-load the external file 3. Write a cookie

Inline + postload •  Later visits: 1. Read cookie 2. Refer to the external file

Web Fonts •  Don’t go overboard! •  Subset •  Gzip! http://snook.ca/archives/html_and_css/ screencast-converting-ttf2eot

Fewer HTTP requests •  Inline images: in CSS sprites with data: URI scheme http://csssprites.com http://spriteme.org

Fewer HTTP requests •  data: URI scheme $ php ‐r "echo base64_encode(file_get_contents('my.png'));” iVBORw0KGgoAAAANSUhEUgAAAAQAAAADCAIAAAA7ljmRAAAAGElEQVQIW2P 4DwcMDAxAfBvMAhEQMYgcACEHG8ELxtbPAAAAAElFTkSuQmCC

Fewer HTTP requests •  data: URI scheme background‐image: url("data:image/ png;base64,iVBORw0KG...");

Fewer HTTP requests •  data: URI scheme <img src="data:image/png;base64,iVBOR..." />

Fewer HTTP requests •  data: URI scheme •  works in IE!...

Fewer HTTP requests •  data: URI scheme •  works in IE8!

Fewer HTTP requests •  data: URI scheme •  MHTML for IE < 8

MHTML •  MIME HTML •  Works in IE 6,7 •  Indeed it actually absolutely does work in IE7/Vista too

MHTML - one part Content-Location: myimage Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSU....U5ErkJggg==

MHTML - multi parts Content-Type: multipart/related; boundary="MYSEPARATOR" --MYSEPARATOR [here comes part one] The double- --MYSEPARATOR dash of doom [here's part two] --MYSEPARATOR--

MHTML – all together /* Content-Type: multipart/related; boundary="MYSEPARATOR" --MYSEPARATOR Content-Location: myimage Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAMAAADXqc3KAAAD....U5ErkJggg== --MYSEPARATOR Content-Location: another Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAMAAADXqc3KAAAA....U5ErkJggg== --MYSEPARATOR-- */ .myclass { background-image:url(mhtml:http://example.org/styles.css!myimage); } .myotherclass { background-image:url(mhtml:http://example.org/styles.css!another); }

MHTML + data URI •  drawback: repeats the same encoded image •  solution: browser-specific CSS •  or… an ingenious hack

MHTML + data URI •  image header + css + data /9j/4AA0;background-image:url(data:image/jpeg;base64;00,/9j/4AA0 Reality: IE: Others: http://habrahabr.ru/blogs/webdev/90761/

No-image UI •  a.k.a. CSS3

Rounded corners .module { -moz-border-radius: 9px; -webkit-border-radius: 9px; border-radius: 9px; }

Rounded corners All  vs. IE

Gradients .hd { background-image: -moz-linear-gradient(top, #641d1c, #f00); background-image: -webkit-gradient(linear, left top, left bottom, from(#641d1c), to(#f00)); filter: [...].gradient(startColorstr=#ff641d1c,endColorstr=#ffff0000); -ms-filter: "[...].gradient(startColorstr=#ff641d1c,endColorstr=#ffff0000)"; }

No-image UI •  rounded corners •  gradients •  glows, shadows •  rgba http://www.phpied.com/ css-performance-ui-with-fewer-images/ http://css3please.com

Multi-purpose “mask” images •  one image on top of different solid colors •  for themes, social profiles…

1px wide “mask” •  Top: somewhat transparent •  Bottom: Fully transparent

Multi-purpose mask

Gradient mask •  the data URI smaller that all the CSS –moz, -webkit, filter...

A glossy mask

Optimizing image file sizes

Rule #1: No GIFs $ optipng *.gif

PNG-8 •  Palette image (like GIF) •  256 colors (like GIF) •  Smaller than GIF (GIF++) •  Alpha transparency (GIF++)

Rarely PNG-24 •  Truecolor

PNGSlim OptiPNG DeflOpt PNGOut PNGOptimizer PNGCrush AdvPNG PNGRewrite

JPEG •  The format for photos •  Run through JPEGTran

Study of the images on the top 1000 sites Q: How many GIFs are out there? Q: What if we make them PNG? Q: Are PNGs optimized? Q: Are JPEGs optimized?

Top 1000 – how? •  URLs from Alexa top sites •  open Fiddler •  php script that opens/closes Explorer with each URL •  enjoy! •  Export images from Fiddler

Top 1000 – GIF vs. PNG? Animated GIF 3% PNG 24% GIF 73%

Top 1000 – GIF vs. PNG vs. JPG? GIF 40% JPEG 46% PNG Animated GIF 13% 1%

Top 1000 – GIF to PNG $ optipng *.gif $ pngoptimizercl – file:"*.png” (1 min/1000 files) 23.79% savings

Top 1000 – Optimizing PNG $ pngoptimizercl – file:"*.png" 16.90% savings

Top 1000 – Optimizing JPG $ jpegtran –copy none -optimize 13.08% savings

Take-home 1.  Think reusable CSS 2.  Reduce HTTP requests: - sprites, data URIs - CSS3, reusable images 3.  Smush all images

Thank you! Stoyan Stefanov @stoyanstefanov http://www.phpied.com

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CSS and image optimization

by Stoyan Stefanov on May 12, 2010

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CSS and image optimization Presentation Transcript