Responsive design is taking the world by a storm and every team is converting their site to be on mobile or preparing to do that soon. Few people however realize performance implications of this new approach to web development and one of the issues is images which represent more then 60% of all network payload and can congest wireless networks with data unnecessary for display on naturally smaller screens than desktop. This issue gave birth to various Responsive Images techniques which are used to display “just right” size of the image for user’s device. There are several aspects of the issue that need to be considered, from formats and resolutions to content management and implementation code.

1. Fast & Responsive
Images
NY Front-End Coders Meetup March 11, 2015

2. Sergey Chernyshev
Organize NY Web Perf
Tech. Dir. Web Sys. &
App. Dev. at truTV /
Turner
@SergeyChe
SergeyChernyshev.com

3. Responsive Design & Images
May 25, 2010 http://alistapart.com/article/responsive-web-design/

4. Image Responsiveness
Size
"Art direction"
Format / Encoding

5. Size in Pixels (resolution)
Size in Kb
on the wire
in memory
+ decoding
"Why we need responsive images"
part I & part II by @TKadlec
1920px 320px

6. Size in Pixels (density)
Multiply by 1 - 3x
Kindle Fire HDX - 2560x1600
iPhone 6 - 1704x960
iPhone 5 - 1136x640
iPad 3, 4, Air - 2048x1536
iMac 5K Retina - 5120x2880
http://dpi.lv/ - DPI Love by Lea Verou

7. Art Direction

8. Encoding: JPEG compression
Lossy: 1-100 quality setting
Lossless: removes metadata
100 90 80 70 60
50 40 30 20 10
100 90 80 70 60
50 40 30 20 10

9. Encoding: Best Format
JPEG
WebP
Chrome23+
Opera 12.1+
JPEG XR
IE10+
PNG
Gif -> PNG
PNG -> JPEG
SVG
Web Site Optimization With Browser-Specific
Image Formats calendar.perfplanet.com

10. Integration: CMS Workflow
Edit
Optimize
Deploy

11. Integration: Image Service
Adaptive Images
<img
src="http://myserver/320/200/http://a.com/b.jpg"
width="320"
height="200"
>
LiquidPixels
https://github.com/MattWilcox/Adaptive-Images

12. <picture>, srcset, sizes
Now part of HTML spec
In current Chrome, Opera, Firefox (38),
"under consideration" in IE
http://responsiveimages.org/

13. On The Page
<?php img('/path/to/original.jpg') ?>
8 Guidelines and 1 Rule for Responsive Images
http://blog.cloudfour.com/8-guidelines-and-1-rule-for-responsive-images/
Picturefill v2 by Scott Jehl
https://github.com/scottjehl/picturefill

14. Integration: Automation
mod_pagespeed / ngx_pagespeed filters
• rewrite_images
• inline_images
• recompress_images
• convert_gif_to_png, convert_png_to_jpeg
FEO from Akamai, Radware and others

15. 0.000
0.400
0.800
1.200
1.600
Small Medium Large
1.454
1.233
0.407
Homepage Image Sizes (Mb)

16. 0.000
1.000
2.000
3.000
4.000
Small Medium Large Source
3.818
1.454
1.233
0.407
Homepage Image Sizes (Mb)

17. Thank you!
Sergey Chernyshev
@SergeyChe
@PerfPlanet
sergey.chernyshev@gmail.com